Java Web foundation of full stack learning

java,web

1. Basic concepts

1.1 Preface

web development:

Web means web page
Static web
- html css
- The data provided to everyone will never change
Dynamic web
- Everyone sees different information at different times and places
- Technology stack: Servlet/Jsp, Asp, PHP

In java, the technology of dynamic web resource development is called javaWeb

1.2. web application

web application: a program that can be provided for browser access

a.html xx.html... Integrate multiple web resources, which can be accessed by the outside world and provide services to the outside world
Any page or resource we can access exists on a computer somewhere in the world
URL
These unified web resources will be placed in the same folder, and the web application depends on Tomcat
A web application consists of several parts (static web, dynamic web)
- html,css,js
- jsp,servlet
- java program
- jar package
- Configuration file (properties)

After the web application is written, if you want to provide access to the outside world: you need a server to manage it uniformly;

1.3. Static web

*.htm
*.html

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Disadvantages of static web
- The web page cannot be refreshed dynamically. All users see the same page. The following methods can be used to improve it
  - Rotation chart
  - Click effect: pseudo dynamic
  - JavaScript
- Unable to interact with the database (data cannot be persisted and users cannot interact)

1.4 dynamic web

The page will be displayed dynamically: it varies from person to person

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shortcoming

There is an error in the dynamic resources added to the server. We need to write a new background program and republish it
- Shutdown maintenance

advantage

web pages can be refreshed dynamically, and all users do not see the same page
Can interact with database (data persistence)
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2. web server

2.1 three technologies

ASP

Microsoft: the earliest popular in China
Embedded VB script ASP + COM in html
In ASP development, there are thousands of lines of business code in a page -- > the maintenance cost is high
Mainly use C#
IIS

PHP

PHP development is fast, powerful, cross platform and simple code
Unable to carry large traffic (limitations)

JSP/Servlet

B/S: browser and server

C/S: client and server

B/S architecture mainly promoted by sun company
Based on Java language
It can bear the impact of the three high problems

2.2. web server

Server is a passive operation, which is used to process some requests and give some responses to users

IIS

Microsoft
Run ASP
Built in Windows

Tomcat

Tomcat is a core project in the Jakarta project of the Apache Software Foundation (Apache). The latest Servlet and JSP specification can always be reflected in Tomcat, because Tomcat technology is advanced, stable and free, which is deeply loved by the fans and has been recognized by some software developers. Become a more popular Web application server.

Tomcat server is a free open source Web application server, which belongs to lightweight application The server , it is widely used in small and medium-sized systems and occasions where there are not many concurrent access users. It is the first choice for developing and debugging JSP programs. For a Java web beginner, it is the best choice

Tomcat actually runs JSP pages and servlets. The latest version of Tomcat is 10.0.14.

Download Tomcat

install
Understand the configuration file and directory structure
effect

3,Tomcat

3.1. Installing Tomcat

Tomcat official website

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Note: tar GZ is the installation package under Linux

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Right click decompression

3.2. Tomcat startup

Role of folders

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Start and close Tomcat

start-up

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Double click this file to run

Enter localhost:8080 / enter in the url address bar of the browser

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Close the Tomcat window directly
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Possible problems

Java environment variables are not configured
Flash back problem: compatibility needs to be configured
Garbled code problem: set in the configuration file

3.3. Tomcat configuration

Modify boot port

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Modify the startup port number, host name in this folder

Configurable ports

The default port number of Tomcat is 8080
mysql: 3306
http: 80
https: 443

<Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />

Configurable host name

The default is localhost – > 127.0.0.1
The default site app location is the webapps folder

 <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">

However, the modified name cannot be accessed successfully

The following practices are required

For example:

name = "www.qinjiang.com"
Modify host in Windows

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Restart Tomcat

Modify home page information

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Here you can modify the information of accessing the home page

<div id="navigation" class="curved container">
                <span id="nav-home"><a href="${tomcatUrl}">Home</a></span>
                <span id="nav-hosts"><a href="${tomcatDocUrl}">Documentation</a></span>
                <span id="nav-config"><a href="${tomcatDocUrl}config/">Configuration</a></span>
                <span id="nav-examples"><a href="${tomcatExamplesUrl}">Examples</a></span>
                <span id="nav-wiki"><a href="https://wiki.apache.org/tomcat/FrontPage">Wiki</a></span>
                <span id="nav-lists"><a href="${tomcatUrl}lists.html">Mailing Lists</a></span>
                <span id="nav-help"><a href="${tomcatUrl}findhelp.html">Find Help</a></span>
                <br class="separator" />
</div>

How is the website accessed

Enter URL enter
Check whether there is a mapping of this domain name under the hosts configuration file under C:\Windows\System32\drivers\etc
1. If yes, directly return the corresponding ip address. There are web programs we need to access in this address, which can be accessed directly
```
127.0.0.1 www.qinjiang.com
```
2. If not, go to the DNS server to find it and return it if found. If not, return it if not found
  
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3.4. Publish a web site

Put the website written by yourself under the specified folder (webapps) of Tomcat server

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Each folder corresponds to localhost:8080 / folder name

Structure of website

—webapps

— root

- scy: directory name of the website

—WEB-INFO

- classes: java program

- lib: the jar package on which the web reference depends

—web.xml: Web site configuration file

—index.html: default home page

- static: static resource

—css

—**.css

—js

—images

—...

4,http

4.1. What is http

Hypertext Transfer Protocol (HTTP) is a simple request response protocol, which usually runs on TCP.

Text html string
Hypertext
- picture
- music
- video
- location
- Map
Port 80

HTTPS (full name: Hyper Text Transfer Protocol over SecureSocket Layer) is an HTTP channel aiming at security. On the basis of HTTP, it ensures the security of the transmission process through transmission encryption and identity authentication.

Port 443

4.2 two times of http

http1.0
- HTTP/1.0: after the client can connect with the web server, it can only obtain one web resource and disconnect
http2.0
- HTTP/1.1: after the client can connect with the web server, it can obtain multiple web resources

4.3 http request

The client sends a request to the server

Baidu

General

Request URL: https://www.baidu.com / / request address
Request method: GET //Request method
Status code: 200 OK //Status code
Remote address: 14.215.177.39:443  //Remote address

Request header

Accept: text/html //type
Accept-Encoding: gzip, deflate, br //Type code
Accept-Language: zh-CN,zh;q=0.9 //language
Cache-Control: max-age=0 //cache control
Connection: keep-alive //connect

Request line

GET mode in request line
Request method: GET, POST, HEAD, DELETE, PUT, trace
- The parameters that get can carry in one request are relatively few, and the size is limited. The content will be displayed in the URL bar of the browser, but it is efficient
- A post request can carry many parameters with unlimited size. It will not display the content in the browser URL, but it is not efficient

Message header

Accept //Tell the browser what data types it supports
Accept-Encoding //Tell the browser the supported encoding format GBK UTF-8 GB2312
Accept-Language //Tell the browser his locale
Cache-Control //Cache control
Connection //Tell the browser whether to disconnect or remain connected after the request
Host //host

4.4 http response

The server returns a response to the client

Baidu

Response header

Cache-Control: private //cache control
Connection: keep-alive //Connect: keep connected
Content-Encoding: gzip  //code
Content-Type: text/html;charset=utf-8 //type

Responder

Accept //Tell the browser the data types it supports
Accept-Encoding //Tell the browser the supported encoding format GBK UTF-8 GB2312
Accept-Language //Tell the browser his locale
Cache-Control //Cache control
Connection //Tell the browser whether to disconnect or remain connected after the request
Host //host
Refresh //Tell the client how often to refresh
Location //Repositioning web pages

Response status code

200 request response successful
3xx request redirection
- Redirect: you return to the new location I gave you
4xx resource not found - 404
- Resource does not exist
5xx server code error - 500
- 502 gateway error

Common interview questions:

When you enter the address in the address bar of your browser and press enter, the page can show back. What has happened?

5,Maven

Why Maven?

In Java Web, we need a large number of jar packages, which we need to import manually
Maven can automatically import and configure jar packages for us

5.1 Maven architecture management tool

We currently use it to import jar packages

Maven's core idea: Convention is greater than configuration

Don't break the rules
Maven will specify how you should write our Java code

5.2 Maven Download

Official website: https://maven.apache.org/

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decompression

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5.3. Configure environment variables

Configure the following in the system environment variable

M2_ bin directory under home Maven directory
MAVEN_HOME maven directory

Configure our Maven in the path of the system_ HOME %MAVEN_ HOME%\bin

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path is also added

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Test whether the configuration is successful

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5.4 Alibaba cloud image

mirrors: Mirror
- Function: accelerate our download
Alibaba cloud image Maven 3 is recommended in China 8.4 self contained, no modification recommended

<mirror>
    <id>nexus-aliyun</id>
    <mirrorOf>*,!jeecg,!jeecg-snapshots</mirrorOf>
    <name>Nexus aliyun</name>
    <url>http://maven.aliyun.com/nexus/content/groups/public</url>
</mirror>

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5.5. Establish local warehouse

Local warehouse

Remote warehouse

Build a local repository

Create a new local folder

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E:\environment\apache-maven-3.8.4\maven-repo

In the conf folder, click settings Add local warehouse location in XML (notepad software used here, if not, right-click to open notepad)

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5.6. Use Maven in idea

Start idea
Create a maven web project

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Click next

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Then set the address of the project file and finish

Then wait for the profile to download

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After the idea is created successfully, we should pay attention to

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Here, it's ok to import maven from idea

5.7. Create a common maven project

Uncheck direct next

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In the case of webapp above

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In the webapp project above, follow the clean maven project and create a new java resources

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5.8. Mark folder function in idea

If your above java resources are inconsistent with mine

Taking java as an example, right-click java

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Or the sources under file – project structure modules can also be set

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5.9. Configure Tomcat in idea

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Click ok

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5.10 pom documents

pom.xml is Maven's core configuration file

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pom file details

<?xml version="1.0" encoding="UTF-8"?>

<!--Maven Version and header file-->
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <!--This is what we just configured GVA-->
  <groupId>com.si</groupId>
  <artifactId>javaweb-01-maven</artifactId>
  <version>1.0-SNAPSHOT</version>
  <!--Packaging method of the project
  jar package -java application
  war package -javaweb application
  -->
  <packaging>war</packaging>


  <!--to configure-->
  <properties>
    <!--Default build code for the project-->
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <!--maven Compiled version of-->
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <!--Project dependency-->
  <dependencies>
    <!--Specific dependent jar package-->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <!--Things for project construction-->
  <build>
    <finalName>javaweb-01-maven</finalName>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

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Because maven's convention is greater than configuration, we may encounter the problem that the configuration file we wrote cannot be exported or take effect. Solution: configure the resource node

<!--stay build Medium configuration resources,To prevent the failure of resource export-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <excludes>
                    <exclude>**/*.properties</exclude>
                    <exclude>**/*.xml</exclude>
                </excludes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>

5.11. idea operation directory tree

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5.12 use of Maven repository

Address: https://mvnrepository.com/

Take servlet API as an example

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6,Servlet

6.1 introduction to servlet

It is a technology for sun company to develop dynamic web
sun provides an interface in these API s - servlet s
If you want to develop a servlet applet, you only need to complete two steps
- Write a class to implement the servlet interface
- Deploy the developed java classes to the web server

The Java code that implements the servlet interface is called servlet

6.2,HelloServlet

Servlet has two implementation interfaces in sun company: HTTPServlet and GenericServlet

Build a maven project and delete the src directory. In the future, we will build a module here. This empty project is the main project of Maven

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New sub module

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Understanding of Maven father son project
1. There is a mudule in the pom in the parent project
```
<modules>
  	<module>servlet-01</module>
</modules>
```
2. The pom in the child project has a parent (if you don't, delete the scope in the parent project pom first)
```
<parent>
    <artifactId>javaweb-02-Servlet</artifactId>
    <groupId>com.si</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>
```

The son project can use the jar package of the father project

Maven environment optimization
1. Modify web XML is the format in the latest version of apache-tomcat-10.0.14\webapps\ROOT\WEB-INF
2. Complete Maven's structure

Create a new servlet program

Write a common class

Implement servlet interface and inherit HTTP Servlet

package com.si.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    //Because Get Post is only a different way of request implementation, it can be called each other, and the business logic is the same

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        PrintWriter writer = resp.getWriter(); //Response flow
        writer.print("Hello Servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

Write the mapping map of Servlet

Why do we need mapping?

Because we write java programs that need to be accessed through the browser, and the browser needs to access the web server, we need to register the Servlet program we write in the web server and give it a mapping that the browser can access

On the web Register in XML

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
                      https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0"
         metadata-complete="true">

    <!--register Servlet-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.si.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--Servlet Request path for-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>hello</url-pattern>
    </servlet-mapping>

</web-app>

Configure Tomcat

Note the configured project publishing path

Start test

6.3 principle of Servlet

The servlet is called by the web server. After receiving the browser request, the web server will

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6.4,Mapping

A Servlet can specify a mapping path

<!--Servlet Request path for-->
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>

A Servlet can specify multiple mapping paths

<!--Servlet Request path for-->
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>

<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello1</url-pattern>
</servlet-mapping>

A Servlet can specify a common mapping path

<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello/*</url-pattern>
</servlet-mapping>

<!--Default request path-->
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/*</url-pattern>
</servlet-mapping>

Specify some prefixes, suffixes, etc

<!--Servlet Request path for-->
<!--as long as.scy Can be accessed /hello/sssss.scy Can also access
 *Item mapping path cannot be added before
-->
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>*.scy</url-pattern>
</servlet-mapping>

Priority issues

The inherent mapping path is specified with the highest priority. If it cannot be found, the default processing request will be taken

<!--Register default Servlet request-->
<servlet>
    <servlet-name>error</servlet-name>
    <servlet-class>com.si.servlet.ErrorServlet</servlet-class>
</servlet>
<!--Servlet Request path for-->
<servlet-mapping>
    <servlet-name>error</servlet-name>
    <url-pattern>/*</url-pattern>
</servlet-mapping>

6.5,ServletContext

When the web container starts, it will create a servletContext object for all web applications, which represents the current web application

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6.51. Shared data

The data I saved in this servlet can also be obtained in another servlet

Placed class

package com.si.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //this.getInitParameter() get initialization parameters
        //this.getServletConfig() get servlet configuration
        //this.getServletContext() get servlet context

        ServletContext servletContext = this.getServletContext();
        String username = "Si Chengyong"; //data
        servletContext.setAttribute("username",username); //A data is saved in the ServletContext with the name username and the value username

        System.out.println("hello");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

Read class

package com.si.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();

        String username = (String) servletContext.getAttribute("username");

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print(username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

Configure web xml

    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.si.servlet.HelloServlet</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>getc</servlet-name>
        <servlet-class>com.si.servlet.GetServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

6.52. Get initialization parameters

<!--Configure initialization parameters-->
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybaits</param-value>
    </context-param>

Get initialization parameters

package com.si.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ServletDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //this.getInitParameter() get initialization parameters
        //this.getServletConfig() get servlet configuration
        //this.getServletContext() get servlet context

        ServletContext servletContext = this.getServletContext();
        String url = servletContext.getInitParameter("url");

        resp.getWriter().print(url);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<servlet>
        <servlet-name>gp</servlet-name>
        <servlet-class>com.si.servlet.ServletDemo03</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>gp</servlet-name>
        <url-pattern>/gp</url-pattern>
    </servlet-mapping>

6.53 request forwarding

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 @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //this.getInitParameter() get initialization parameters
        //this.getServletConfig() get servlet configuration
        //this.getServletContext() get servlet context

        System.out.println("Entered servletDemo04");
        ServletContext servletContext = this.getServletContext();
        /* Write separately
        RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/gp"); //Forwarded request path
        requestDispatcher.forward(req,resp); //Call forward to forward the request
        */
        servletContext.getRequestDispatcher("/gp").forward(req,resp);
    }

6.54. Read resource files

properties

Create properties under java
Create properties under resources

The discovery is packaged in the same path (classes, commonly known as classpath)

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properties file

username=root
password=123456

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        ServletContext servletContext = this.getServletContext();
        InputStream resourceAsStream = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");//Read resources
        Properties properties = new Properties();
        properties.load(resourceAsStream); //Load resource content

        System.out.println("account" + properties.get("username") + "password" + properties.get("password"));

    }

<servlet>
        <servlet-name>sd5</servlet-name>
        <servlet-class>com.si.servlet.ServletDemo05</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>sd5</servlet-name>
        <url-pattern>/sd5</url-pattern>
    </servlet-mapping>

6.6,(HttpServlet)Request

(HttpServlet)Request represents the request of the client. The user accesses the server through the Http protocol. All the information in the Http request will be encapsulated in the HttpServletRequest. Through this HttpServletRequest method, all the information of the client can be obtained

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6.61. Obtain the information transmitted by the front end and forward the request

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package com.si.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //The background accepts Chinese garbled code
        req.setCharacterEncoding("UTF-8");
        //Chinese garbled code at the front desk
        resp.setCharacterEncoding("UTF-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbies = req.getParameterValues("hobby"); //Get multiple values, multiple check boxes


        System.out.println("username:" + username + "\t password:" + password + "\nhobbies:" + Arrays.toString(hobbies));
        //redirect
        //resp.sendRedirect("/r2/success.jsp");

        /// here represents the current web application when forwarding the request, so / r2 is not added
        req.getRequestDispatcher("/success.jsp").forward(req,resp);
    }
}

Interview question: the relationship between redirection and forwarding

Same point
- Page Jump
difference
- The URL will not change when the request is forwarded 307
- When redirecting, the URL will change 302

6.7,(HttpServlet)Response

The web server receives the http request from the client. For this request, an HttpServletRequest object representing the request and an HttpServletResponse request representing the response are created respectively

Get the parameter HttpServletRequest requested from the client
If you want to respond to some information to the client, HttpServletResponse

6.71 simple classification

Method responsible for sending data to browser

getOutputStreampublic ServletOutputStream getOutputStream() throws IOException;

public PrintWriter getWriter() throws IOException;

Method responsible for sending response header to browser

public void setCharacterEncoding(String charset);
public void setContentLength(int len);
public void setContentLengthLong(long len);
public void setContentType(String type);
public void setDateHeader(String name, long date);
public void addDateHeader(String name, long date);
public void setHeader(String name, String value);
public void addHeader(String name, String value);
public void setIntHeader(String name, int value);
public void addIntHeader(String name, int value);

Response status code

    /**
     * Status code (100) indicating the client can continue.
     */
    public static final int SC_CONTINUE = 100;

    /**
     * Status code (101) indicating the server is switching protocols
     * according to Upgrade header.
     */
    public static final int SC_SWITCHING_PROTOCOLS = 101;

    /**
     * Status code (200) indicating the request succeeded normally.
     */
    public static final int SC_OK = 200;

    /**
     * Status code (201) indicating the request succeeded and created
     * a new resource on the server.
     */
    public static final int SC_CREATED = 201;

    /**
     * Status code (202) indicating that a request was accepted for
     * processing, but was not completed.
     */
    public static final int SC_ACCEPTED = 202;

    /**
     * Status code (203) indicating that the meta information presented
     * by the client did not originate from the server.
     */
    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;

    /**
     * Status code (204) indicating that the request succeeded but that
     * there was no new information to return.
     */
    public static final int SC_NO_CONTENT = 204;

    /**
     * Status code (205) indicating that the agent <em>SHOULD</em> reset
     * the document view which caused the request to be sent.
     */
    public static final int SC_RESET_CONTENT = 205;

    /**
     * Status code (206) indicating that the server has fulfilled
     * the partial GET request for the resource.
     */
    public static final int SC_PARTIAL_CONTENT = 206;

    /**
     * Status code (300) indicating that the requested resource
     * corresponds to any one of a set of representations, each with
     * its own specific location.
     */
    public static final int SC_MULTIPLE_CHOICES = 300;

    /**
     * Status code (301) indicating that the resource has permanently
     * moved to a new location, and that future references should use a
     * new URI with their requests.
     */
    public static final int SC_MOVED_PERMANENTLY = 301;

    /**
     * Status code (302) indicating that the resource has temporarily
     * moved to another location, but that future references should
     * still use the original URI to access the resource.
     *
     * This definition is being retained for backwards compatibility.
     * SC_FOUND is now the preferred definition.
     */
    public static final int SC_MOVED_TEMPORARILY = 302;

    /**
    * Status code (302) indicating that the resource reside
    * temporarily under a different URI. Since the redirection might
    * be altered on occasion, the client should continue to use the
    * Request-URI for future requests.(HTTP/1.1) To represent the
    * status code (302), it is recommended to use this variable.
    */
    public static final int SC_FOUND = 302;

    /**
     * Status code (303) indicating that the response to the request
     * can be found under a different URI.
     */
    public static final int SC_SEE_OTHER = 303;

    /**
     * Status code (304) indicating that a conditional GET operation
     * found that the resource was available and not modified.
     */
    public static final int SC_NOT_MODIFIED = 304;

    /**
     * Status code (305) indicating that the requested resource
     * <em>MUST</em> be accessed through the proxy given by the
     * <code><em>Location</em></code> field.
     */
    public static final int SC_USE_PROXY = 305;

     /**
     * Status code (307) indicating that the requested resource 
     * resides temporarily under a different URI. The temporary URI
     * <em>SHOULD</em> be given by the <code><em>Location</em></code> 
     * field in the response.
     */
    public static final int SC_TEMPORARY_REDIRECT = 307;

    /**
     * Status code (400) indicating the request sent by the client was
     * syntactically incorrect.
     */
    public static final int SC_BAD_REQUEST = 400;

    /**
     * Status code (401) indicating that the request requires HTTP
     * authentication.
     */
    public static final int SC_UNAUTHORIZED = 401;

    /**
     * Status code (402) reserved for future use.
     */
    public static final int SC_PAYMENT_REQUIRED = 402;

    /**
     * Status code (403) indicating the server understood the request
     * but refused to fulfill it.
     */
    public static final int SC_FORBIDDEN = 403;

    /**
     * Status code (404) indicating that the requested resource is not
     * available.
     */
    public static final int SC_NOT_FOUND = 404;

    /**
     * Status code (405) indicating that the method specified in the
     * <code><em>Request-Line</em></code> is not allowed for the resource
     * identified by the <code><em>Request-URI</em></code>.
     */
    public static final int SC_METHOD_NOT_ALLOWED = 405;

    /**
     * Status code (406) indicating that the resource identified by the
     * request is only capable of generating response entities which have
     * content characteristics not acceptable according to the accept
     * headers sent in the request.
     */
    public static final int SC_NOT_ACCEPTABLE = 406;

    /**
     * Status code (407) indicating that the client <em>MUST</em> first
     * authenticate itself with the proxy.
     */
    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;

    /**
     * Status code (408) indicating that the client did not produce a
     * request within the time that the server was prepared to wait.
     */
    public static final int SC_REQUEST_TIMEOUT = 408;

    /**
     * Status code (409) indicating that the request could not be
     * completed due to a conflict with the current state of the
     * resource.
     */
    public static final int SC_CONFLICT = 409;

    /**
     * Status code (410) indicating that the resource is no longer
     * available at the server and no forwarding address is known.
     * This condition <em>SHOULD</em> be considered permanent.
     */
    public static final int SC_GONE = 410;

    /**
     * Status code (411) indicating that the request cannot be handled
     * without a defined <code><em>Content-Length</em></code>.
     */
    public static final int SC_LENGTH_REQUIRED = 411;

    /**
     * Status code (412) indicating that the precondition given in one
     * or more of the request-header fields evaluated to false when it
     * was tested on the server.
     */
    public static final int SC_PRECONDITION_FAILED = 412;

    /**
     * Status code (413) indicating that the server is refusing to process
     * the request because the request entity is larger than the server is
     * willing or able to process.
     */
    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;

    /**
     * Status code (414) indicating that the server is refusing to service
     * the request because the <code><em>Request-URI</em></code> is longer
     * than the server is willing to interpret.
     */
    public static final int SC_REQUEST_URI_TOO_LONG = 414;

    /**
     * Status code (415) indicating that the server is refusing to service
     * the request because the entity of the request is in a format not
     * supported by the requested resource for the requested method.
     */
    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;

    /**
     * Status code (416) indicating that the server cannot serve the
     * requested byte range.
     */
    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;

    /**
     * Status code (417) indicating that the server could not meet the
     * expectation given in the Expect request header.
     */
    public static final int SC_EXPECTATION_FAILED = 417;

    /**
     * Status code (500) indicating an error inside the HTTP server
     * which prevented it from fulfilling the request.
     */
    public static final int SC_INTERNAL_SERVER_ERROR = 500;

    /**
     * Status code (501) indicating the HTTP server does not support
     * the functionality needed to fulfill the request.
     */
    public static final int SC_NOT_IMPLEMENTED = 501;

    /**
     * Status code (502) indicating that the HTTP server received an
     * invalid response from a server it consulted when acting as a
     * proxy or gateway.
     */
    public static final int SC_BAD_GATEWAY = 502;

    /**
     * Status code (503) indicating that the HTTP server is
     * temporarily overloaded, and unable to handle the request.
     */
    public static final int SC_SERVICE_UNAVAILABLE = 503;

    /**
     * Status code (504) indicating that the server did not receive
     * a timely response from the upstream server while acting as
     * a gateway or proxy.
     */
    public static final int SC_GATEWAY_TIMEOUT = 504;

    /**
     * Status code (505) indicating that the server does not support
     * or refuses to support the HTTP protocol version that was used
     * in the request message.
     */
    public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

6.72 downloading files

Output message to browser

Download File

Gets the path to the downloaded file
Downloaded file name
Set up a way to make the browser support downloading what we need
Gets the input stream of the downloaded file
Create buffer
Get outputstream object
Write Fileoutputstream to buffer
Use outputstream to output the data of the buffer to the client

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. Get the path of the downloaded file
        String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/images/1.png");
        System.out.println("True path of file:" + realPath);
        //2. Downloaded file name
        String FileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        System.out.println(FileName);

        //3. Set up a way to make the browser support (content disposition) to download what we need. The Chinese file name is urlencoder Encode solution
        resp.setHeader("Content-Disposition","attachment;filename=" + URLEncoder.encode(FileName,"UTF-8"));
        //4. Obtain the input stream of the downloaded file
        FileInputStream in = new FileInputStream(realPath);
        //5. Create buffer
        int len = 0;
        byte[] buffer = new byte[1024];
        //6. Get outputstream object
        ServletOutputStream out = resp.getOutputStream();
        //7. Write Fileoutputstream to the buffer and use outputstream to output the data of the buffer to the client
        while ((len=in.read(buffer)) > 0) {
            out.write(buffer,0,len);
        }

        in.close();
        out.close();
    }

6.73 verification code function

How do I get the verification code?

Front end implementation js
The back-end implementation needs to use the java picture class to generate a picture

package com.si.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //How to make the browser refresh automatically every 5 seconds
        resp.setHeader("refresh","3");

        //Create a picture in memory
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //Get pictures
        Graphics2D graphics = (Graphics2D)image.getGraphics(); //A brush
        //Set the background color of the picture
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0,0,80,20);
        //Write data to pictures
        graphics.setColor(Color.BLUE);
        graphics.setFont(new Font(null, Font.BOLD,20));
        graphics.drawString(makeRandomArray(),0,20);
        //Tell the browser to open the request as a picture
        resp.setContentType("image/png");

        //There is a cache on the website. Do not let the browser cache
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //Write the picture to the browser
        boolean is_ok = ImageIO.write(image,"jpg" ,resp.getOutputStream());
    }

    //Generate random number
    private String makeRandomArray() {
        Random random = new Random();
        String array = String.valueOf(random.nextInt(9999999));
        StringBuffer sb = new StringBuffer();

        //If the length is not enough, fill 0 with 7
        for (int i = 0; i < 7-array.length(); i++) {
            sb.append("0");
        }
        array = sb.toString() + array;
        return array;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

6.74 redirection

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After a web resource receives a client request, it will notify the client to access another web resource. This process is called redirection.

Common scenarios:

User login

public void sendRedirect(String location) throws IOException;

test

resp.sendRedirect("/r1/image");

Equivalent to the following

resp.setHeader("Location","/r1/image");
resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);

Interview question: the relationship between redirection and forwarding

Same point
- Page Jump
difference
- The URL will not change when the request is forwarded
- The URL will change during redirection

7,Session,Cookie

7.1 conversation

Session: users open a browser, click many hyperlinks, access multiple web resources, and close the browser. This process is called session.

Stateful conversation: a classmate has been to the classroom. Next time we come back, we will know that this classmate has been to the classroom

How can you prove that you are Chinese?

Resident ID card of the people's Republic of China -- the ID card given to you by the state
The country has registered you -- the country marks you as Chinese

How does a website prove you've been here

Client server

The server sends a letter to the client, and the client can bring the letter to the server next time Cookie
The server registers that you have been here. Next time you come, I'll match you; - Session

7.2. Two techniques for saving sessions

Client Technology (Response,Request)

Session

Server side technology. Using this technology, we can save the user's Session information. We can put the information or data in the Session

Common scenarios:

After the website is logged in, you can log in directly the next time you visit

7.3,Cookie

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Get cookie information from the request
The server responds to the client

//cookie, the server obtains the request from the client
//Returns an array indicating that there may be multiple cookies
Cookie[] cookies = req.getCookies();

//Get the name of the cookie
String name = cookie.getName();

//Get cookie Value value of name
cookie.getValue()
    
//Create a new cookie
Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis() + "");

//Cookies are valid for one day
cookie.setMaxAge(24*60*60);

//The server gives the client a cookie
resp.addCookie(cookie);

Cookies are generally saved in the local user directory appdata;

Is there an upper limit for a website cookie?

A cookie can only hold one piece of information
A web site can send multiple cookie s to the browser, but can store up to 20
The cookie size is limited to 4KB
The browser can accept cookie s up to 300

delete cookie

If the validity period is not set, it will be deleted automatically when the browser is closed
Set the validity period. The validity period is 0

Prevent garbled code -- encoding and decoding

URLEncoder.encode("Si Chengyong","utf-8") //code
URLDecoder.decode(cookie.getValue(),"utf-8") //decode

7.4. Session (key)

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What is a Session?

The server will create a Session object for each user (browser)
A Session monopolizes a browser. As long as the browser is not closed, the Session exists
After a user logs in, he can access session -- > to save user information and shopping cart information throughout the website

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Use of Session

//Get Session
HttpSession session = req.getSession();

 //Pass something to Session
session.setAttribute("name",new Person("Si Chengyong",21));

//Get the id of the session
String id = session.getId();

 //Judge whether the session is newly created
boolean aNew = session.isNew();

//What did the Session do when it was created
//Cookie cookie = new Cookie("JSESSIONID", session.getId());
//resp.addCookie(cookie);

 //Get Session
 HttpSession session = req.getSession();

//Get property value
 Object person = session.getAttribute("name");

session.removeAttribute("name");
//Log off Session manually
session.invalidate();

Session expires automatically

<!--set up Session Default expiration time-->
<session-config>
    <!--1min after Session Automatic failure-->
    <session-timeout>1</session-timeout> 
</session-config>

The difference between Session and Cookie

Cookie is to write the user's data to the user's browser, and the browser saves it (multiple can be saved)
Session is to write the user's data into the user's exclusive session and save it on the server side (save important information and reduce the waste of server resources)
The Session object is created by the server

Usage scenario:

Save a user's login information
Save cart information
The data that is often used in the whole website is saved in the Session

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8,JSP

8.1. What is JSP

Java Server Pages: Java server pages, like servlets, are used to develop dynamic web technology

Biggest features:

Writing JSP is like writing HTML
difference:
- HTML provides users with static data
- Java code can be embedded in JSP pages to provide users with dynamic data

8.2 JSP principle

Idea: how does JSP execute?

There are no problems at the code level
Server Internal:

There is a work directory in Tomcat; If Tomcat is used in Idea, a work directory will be produced in Tomcat

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The source code address that can be found on my computer
```
E:\environment\apache-tomcat-10.0.14\work\Catalina\localhost\ROOT\org\apache\jsp
```
Finally, the jsp page is converted into a java file

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The browser sends a request to the server. No matter what resource is accessed, it is actually accessing the Servlet

JSP will eventually be converted into Java classes

JSP is essentially a Servlet

public void _jspInit() {
  }

  public void _jspDestroy() {
  }

  public void _jspService(final jakarta.servlet.http.HttpServletRequest request, final jakarta.servlet.http.HttpServletResponse response)
      throws java.io.IOException, jakarta.servlet.ServletException {
  }

Judgment request

Built in some objects Tomcat9

final jakarta.servlet.jsp.PageContext pageContext; //page
javax.servlet.http.HttpSession session; //session
final jakarta.servlet.ServletContext application; //applicationContext
final jakarta.servlet.ServletConfig config; //config
javax.servlet.jsp.JspWriter out = null; //out
final java.lang.Object page = this; //page: current
HttpServletRequest request //request
HttpServletResponse response //response

Enter the code added before the page

response.setContentType("text/html;charset=UTF-8"); //Set the page type of the response
pageContext = _jspxFactory.getPageContext(this, request, response,
                                          null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;

The above objects can be directly applied in JSP

principle

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In JSP, as long as it is Java code, it will be output intact

If it is HTML code, it will be converted to out write()

8.3. JSP basic syntax

Any language has its own syntax. JSP, as an application of Java, also has its own extended syntax (understand). All Java grammars support it!

JSP expression

 <%--JSP expression
  Used to output the output of the program to the client
  <%= Variable or expression%>
  --%>
  <%= new Date()%>

JSP script fragment

<%--JSP Script fragment--%>
  <hr>
  <%
    int sum = 0;
    for (int i = 0; i < 100; i++) {
      sum += i;
    }
    out.println("<h1>sum = " + sum + "</h1>");
  %>

Re implementation of script fragments

 <%
    int x = 10;
    out.print(x);
  %>
  <p>This is a JSP file</p>
  <%
    int y = 1;
    out.print(y);
  %>
  <hr>

  <%--Embedding in code HTML element--%>
  <%
    for (int i = 0; i < 5; i++) {

  %>
    <h1>Hello world! <%= i%></h1>
  <%
    }
  %>

JSP declaration

<%!
    static {
      System.out.println("Loading Servlet!");
    }

    private static int globalVar = 0;
    public static void si() {
      System.out.println("Hello!");
    }
  %>

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The JSP declaration will be compiled into the java class generated by JSP, and the other three will be generated into**_ jspService * * method

Just embed java code in JSP

<%%> Code snippet
<%= %> jsp expression
<%! %> jsp statement

8.4. JSP instruction

<%@ page args... %>
<%@include file=""%> Extract public pages

Custom error page

First kind

<%@ page errorPage="error/500.jsp" %>

<%--500.jsp--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>500</title>
</head>
<body>

<img src="../images/500.png" alt="Server error">

</body>
</html>

The second web Configuration in XML

<error-page>
    <error-code>404</error-code> Error type
    <location>/error/404.jsp</location> Address of the response error page
</error-page>

<error-page>
    <error-code>500</error-code>
    <location>/error/500.jsp</location>
</error-page>

Extract public pages

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <%@ include file="common/header.jsp"%>
    <h1>Web Theme</h1>
    <%@ include file="common/footer.jsp"%>

    <%--jsp label
     common Add it before you want it/
    --%>
    <jsp:include page="/common/header.jsp"/>
    <h1>Web Theme</h1>
    <jsp:include page="/common/footer.jsp"/>
</body>
</html>

The difference between the two methods

include file is to get the content

If there is an int x = 1 in the include file

If int x = 10 is also introduced, an error will be reported and the definition will be repeated

out.write("<h1>I am header</h1>");
out.write("\r\n");
out.write("    <h1>Web Theme</h1>\r\n");
out.write("    ");
out.write("\r\n");
out.write("\r\n");
out.write("<h1>I am footer</h1>\r\n");

jsp tags are spliced page essence or three

static {
    _jspx_dependants = new java.util.HashMap<java.lang.String,java.lang.Long>(2);
    _jspx_dependants.put("/common/header.jsp", Long.valueOf(1642820803792L));
    _jspx_dependants.put("/common/footer.jsp", Long.valueOf(1642820837149L));
  }

org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "/common/header.jsp", out, false);
out.write("\r\n");
out.write("    <h1>Web Theme</h1>\r\n");
out.write("    ");
org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "/common/footer.jsp", out, false);

8.5 and 9 built-in objects

PageContext stores data
Request store data
Response
Session store data
Application (ServletContext) stores data
Config (ServletConfig)
Out
Page
Exception

<%
pageContext.setAttribute("name1","Si Chengyong 1"); //The saved page is only valid in one page
request.setAttribute("name2","Si Chengyong 2"); //The saved data is valid only in one request
session.setAttribute("name3","Si Chengyong 3"); //The saved data is valid in one session (from opening the browser to closing the browser or the session expires)
application.setAttribute("name4","Si Chengyong 4"); //The saved data is valid in the server, from opening the server to closing the server
%>

Request: the client sends a request to the server, and the generated data is useless after the user reads it, such as news

session: the client sends a request to the server. The generated data is still useful when the user runs out, such as a shopping cart

Application: when the client sends a request to the server, the generated data may be used up by one user, but other users may still be able to use it, such as chat data

/*Get the search method through pageContext
        * From the bottom to the top (SCOPE)
        * */
String name1 = (String) pageContext.findAttribute("name1");
String name2 = (String) pageContext.findAttribute("name2");
String name3 = (String) pageContext.findAttribute("name3");
String name4 = (String) pageContext.findAttribute("name4");
String name5 = (String) pageContext.findAttribute("name5"); //Nonexistent data

<%--use EL Expression output ${}--%>
<h1>The extracted value is: ${name1}</h1>
<h1>The extracted value is: ${name2}</h1>
<h1>The extracted value is: ${name3}</h1>
<h1>The extracted value is: ${name4}</h1>
<h1>The extracted value is: ${name5}</h1> null
    
pageContext.setAttribute("hello","hello",PageContext.SESSION_SCOPE);
    // Equivalent to session setAttribute

pageContext Medium setAttribute method
public void setAttribute (String name,
			    Object attribute,
			    int scope)
  {
    switch (scope) {
    case PAGE_SCOPE: 
      mPage.put (name, attribute);
      break;
    case REQUEST_SCOPE: 
      mRequest.put (name, attribute);
      break;
    case SESSION_SCOPE: 
      mSession.put (name, attribute);
      break;
    case APPLICATION_SCOPE: 
      mApp.put (name, attribute);
      break;
    default:
      throw new IllegalArgumentException  ("Bad scope " + scope);
    }
  }

8.6. JSP tag, JSTL tag, EL expression

<!--JSTL Dependency of expression-->
<dependency>
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
</dependency>
<!--standard Tag library-->
<dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>

EL expression ${}

get data
Perform operations
Get common objects of web Development
Call Java method

JSP tag

<%--Parameters can be carried during forwarding--%>
    <jsp:forward page="/jsptag2.jsp">
        <jsp:param name="name" value="sichenyong"/>
        <jsp:param name="age" value="21"/>
    </jsp:forward>
        
<%--Take parameters--%>
    <span>name:</span><%=request.getParameter("name")%></br>
    <span>Age:</span><%=request.getParameter("age")%>

JSTL expression

JSTL tag library is used to make up for the shortcomings of HTML tags. It has customized many tags for me to use. The tag function is the same as that of Java code

JSTL rookie tutorial

Core label

The header must be introduced

<%@ taglib prefix="c" 
    	   uri="http://java.sun.com/jsp/jstl/core" %>

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Use steps
- Introduce the corresponding taglib tag header
- Use his method
- JSTL standard jar package should also be introduced into Tomcat, otherwise the parsing failure error will be reported

c:if test

<body>
    <h4>if test</h4>
    <hr>
    <form action="coreif.jsp" method="get">
        <%--EL Expression to get the data in the form
            ${param.Parameter name}
        --%>
        <input type="text" name="username" value="${param.username}">
            <input type="submit" value="Sign in">
    </form>
    <%--
    Judge that if the submitted user name is administrator, the submission is successful
    --%>
    <%--<%
        if (request.getParameter("username").equals("admin")) {
            out.print("Login succeeded!");
        }
    %>--%>
    <%--
    test: Judgment text
    var: The return value variable name is true false
    scope: Scope
    --%>
    <c:if test="${param.username == 'admin'}" var="isAdmin" scope="request">
        <c:out value="Welcome! My dear administrator"/>
    </c:if>
    <c:out value="${isAdmin}"/>
</body>

Corechen test

<body>

    <%--Defines an achievement 87--%>
    <c:set var = "score" value="87"/>

    <%--amount to Switch--%>
    <c:choose>
        <c:when test="${score >= 90}">
            excellent
        </c:when>
        <c:when test="${score >= 80 && score < 90}">
            good
        </c:when>
        <c:when test="${score >= 60 && score < 80}">
            pass
        </c:when>
    </c:choose>

</body>

coreforeach

<body>
    <%
        ArrayList<String> people = new ArrayList<>();
        people.add(0,"Zhang San a");
        people.add(1,"Zhang San");
        people.add(2,"Li Si");
        people.add(3,"Wang Wu");
        people.add(4,"Zhao Liu");
        people.add(5,"pseudo-ginseng");
        request.setAttribute("list",people);
    %>

    <%--
    var Variables traversed each time
    items Array to be traversed
    --%>
    <c:forEach var="people" items="${list}">
        <c:out value="${people}"/> <br>
    </c:forEach>

    <%--
    var Variables traversed each time
    items Array to be traversed
    begin Start subscript
    end End subscript
    step step
    --%>
    <c:forEach var="people" items="${list}" begin="1" end="3" step="2">
        <c:out value="${people}"/> <br>
    </c:forEach>
</body>

Format label
- Lead in head
```
<%@ taglib prefix="fmt" 
           uri="http://java.sun.com/jsp/jstl/fmt" %>
```
- Related operations
  
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SQL tag
- Lead in head
```
<%@ taglib prefix="sql" 
           uri="http://java.sun.com/jsp/jstl/sql" %>
```
- Related operations
  
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XML tag
- Lead in head
```
<%@ taglib prefix="x" 
           uri="http://java.sun.com/jsp/jstl/xml" %>
```
- Related operations
  
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JSTL function
- Lead in head
```
<%@ taglib prefix="fn" 
           uri="http://java.sun.com/jsp/jstl/functions" %>
```
- Related operations
  
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9,JavaBean

Entity class

JavaBean s have a fixed way of writing

There must be a parameterless construct
Property must be privatized
There must be a corresponding get/set method

The ORM is generally used to map fields in the database

ORM: object mapping relationship

Table -- > class
Fields -- > Properties
Row record -- > object

people table

id	name	age
1	Si Chengyong 1	13
2	Si Chengyong 2	17
3	Si Chengyong 3	21

class People {
    private Integer id;
    private String name;
    private Integer age;
}

new People(4,"Si Chengyong 4",25);

filter
File upload
Mail sending
JDBC review: how to use JDBC, JDBC crud, JDBC transaction
GUI listener

10. MVC three-tier architecture

10.1. What is MVC

Model View Controller

Early years

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Users directly access the control layer, and the control layer can directly operate the database

servlet --> crud --> database

Disadvantages: the program is bloated, which is not conducive to maintenance
servlet In the code of: processing request, response, view jump, processing JDBC,Processing business code and processing logic code

In the idea of architecture, nothing can not be solved by adding a layer
    programmer
      |
    JDBC
      |
mysql oracle sqlServer..

10.2 three tier architecture

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Model

Business processing: business logic (Service layer)
Data persistence layer: CRUD(Dao layer)

View

Display data
Provide connection and initiate Servlet request (a,form,image...)

Controller(Servlet)

Receive user's request (request: request parameters, session, cookie)
Give it to the business layer to process the corresponding code

Control view jump

Sign in --> Receive user's request --> Processing user requests(Get user login parameters:username password) --> Give it to the business layer to handle the login business(Judge whether the user name and password are correct, and the transaction) --> Dao Check whether the user name and password are correct --> database

11. Filter (important)

Shiro

Filter: filter, which is used to filter the data of the website

Deal with Chinese garbled code
validate logon

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Filter development steps: implement the interface and rewrite the corresponding method

Guide Package

Write filter

Do not import javax by mistake servlet.*; implements Filter

package com.si.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
    //Initializing the web server startup filter starts the characterencoding filter initialization!
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter initialization!");
    }

    /*
        1.All codes in the filter will be executed when filtering specific requests
        2.The filter must continue to pass through filterchain doFilter(servletRequest,servletResponse)
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");

        System.out.println("CharacterEncodingFilter Before execution....");

        filterChain.doFilter(servletRequest,servletResponse); //Let our request continue. If we don't write, the program will be intercepted and stopped

        System.out.println("CharacterEncodingFilter After execution....");
    }

    //When the destruction server is shut down, the characterencoding filter will be destroyed!
    @Override
    public void destroy() {
        System.out.println("CharacterEncodingFilter Destroy!");
    }
}

web. Configure filter filter in XML

<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.si.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <!--As long as it is/servlet Any request under will pass through this filter-->
    <url-pattern>/servlet/*</url-pattern>
</filter-mapping>

12. Listener listener

Implement the interface of a listener: (N kinds)

Write a listener

Implement the interface of listener

package com.si.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

//Count the number of people online -- count the number of session s
public class OnlineListener implements HttpSessionListener {
    //Create Session listener
    //Once a session is created, this event will be triggered
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        ServletContext servletContext = se.getSession().getServletContext();
        System.out.println(se.getSession().getId());
        Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount");
        if (onlineCount == null) {
            onlineCount = new Integer(1);
        } else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count + 1);
        }
        servletContext.setAttribute("OnlineCount",onlineCount);
    }

    //Destroy Session listening
    //This event will be triggered once a Session is destroyed
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext servletContext = se.getSession().getServletContext();
        Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount");
        if (onlineCount == null) {
            onlineCount = new Integer(0);
        } else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count - 1);
        }
        servletContext.setAttribute("OnlineCount",onlineCount);

        //Destroy Session
        // Manual configuration
        // Or web Configure automatic destruction time in XML
        se.getSession().invalidate();
    }
}

web. Configuring listeners in XML

<!--Register listener-->
<listener>
    <listener-class>com.si.listener.OnlineListener</listener-class>
</listener>

13. Common applications of filters and listeners

package com.si.listener;

import java.awt.*;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

public class TestPanel {
    public static void main(String[] args) {
        //Create a new form
        Frame frame = new Frame("happy new year");
        //Create a new panel
        Panel panel = new Panel(null);
        //Set the layout of the form
        frame.setLayout(null);

        frame.setBounds(300,300,500,500);
        //Set background color
        frame.setBackground(new Color(0,0,255));
        panel.setBounds(50,50,300,300);
        panel.setBackground(new Color(255,0,0));
        frame.add(panel);

        frame.setVisible(true);

        //Listen for closing events
        frame.addWindowListener(new WindowListener() {
            @Override
            public void windowOpened(WindowEvent e) {
                System.out.println("open");
            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("Closing");
                System.exit(0);
            }

            @Override
            public void windowClosed(WindowEvent e) {
                System.out.println("close");
            }

            @Override
            public void windowIconified(WindowEvent e) {

            }

            @Override
            public void windowDeiconified(WindowEvent e) {

            }

            @Override
            public void windowActivated(WindowEvent e) {
                System.out.println("Activated");
            }

            @Override
            public void windowDeactivated(WindowEvent e) {
                System.out.println("not active");
            }
        });
    }
}

Users can enter the home page only after logging in. Users cannot enter the home page after logging out

After logging in, put the user's data into the Session

When entering the home page, judge whether the user has logged in

Add the following code to the login success page

<%
    Object user_session = request.getSession().getAttribute("USER_SESSION");
    if (user_session == null) {
        response.sendRedirect("/Login.jsp");
    }
%>

Filter

Implement filter interface

package com.si.filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SysFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        Object userSession = request.getSession().getAttribute("USER_SESSION");
        if (userSession == null) {
            response.sendRedirect("/error.jsp");
        }

        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

web. Configuration in XML

<filter>
    <filter-name>filter</filter-name>
    <filter-class>com.si.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>filter</filter-name>
    <url-pattern>/sys/*</url-pattern>
</filter-mapping>

14,JDBC

What is JDBC

What is JDBC: java database connector

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JDBC basic experiment

The jar package needs to be imported

java.sql
javax.sql
MySQL connector Java -- > connection driver

Construction of experimental environment

Create a new database and a new table Users (id, name, password, email,birthdate)

Import database dependencies

<!--mysql Drive of-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.26</version>
</dependency>

Connect to database in IDEA

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Create a new class - JdbcTest(Statement)

package com.si.test;

import java.sql.*;

public class JdbcTest {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        /*
        characterEncoding=utf-8&useUnicode=true Solve Chinese garbled code
        useSSL=true Secure connection
        timeZone=utc time zone
         */
        String url = "jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&useUnicode=true&useSSL=true&timeZone=utc";
        String username = "root";
        String password = "123456";

        //1. Load driver class
        Class.forName("com.mysql.cj.jdbc.Driver");
        //2. Connect to the database to represent the database
        Connection connection = DriverManager.getConnection(url, username, password);

        //3. Send Statement: curd of sql object to database
        Statement statement = connection.createStatement();

        //4. Write sql
        String sql = "select * from Users where id = 1";

        //5. Execute the query sql statement to return a result set
        ResultSet resultSet = statement.executeQuery(sql);

        /*
        sql = "delete * from Users where id = 4";
        //i == Number of rows affected
        int i = statement.executeUpdate(sql);
        */


        while (resultSet.next()) {
            System.out.println("id:" + resultSet.getObject("id") + "name:" + resultSet.getObject("name"));
        }

        //6. Close the connection to release resources. Open first and then close
        resultSet.close();
        statement.close();
        connection.close();

    }
}

Create a new JDBC test class (PreparedStatement)

package com.si.test;

import java.sql.*;

public class JDBCTest2 {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
               /*
        characterEncoding=utf-8&useUnicode=true Solve Chinese garbled code
        useSSL=true Secure connection
        timeZone=utc time zone
         */
        String url = "jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&useUnicode=true&useSSL=true&timeZone=utc";
        String username = "root";
        String password = "123456";

        //1. Load driver class
        Class.forName("com.mysql.cj.jdbc.Driver");
        //2. Connect to the database to represent the database
        Connection connection = DriverManager.getConnection(url, username, password);
        //3. Write sql
        String sql = "select * from Users where id = ?";

        //4. Precompile
        PreparedStatement pst;
        pst = connection.prepareStatement(sql);
        pst.setObject(1,2); //For the first placeholder? The value of is copied to 2

        //5. Execute sql to obtain the result set
        ResultSet resultSet = pst.executeQuery();
        while(resultSet.next()) {
            System.out.println("id: " + resultSet.getInt("id"));
            System.out.println("name: " + resultSet.getString("name"));
            System.out.println("password: " + resultSet.getString("password"));
            System.out.println("email: " + resultSet.getString("email"));
            System.out.println("birthdate: " + resultSet.getDate("birthdate"));
        }

        //6. Close the link
        resultSet.close();
        pst.close();
        connection.close();
    }
}

JDBC transaction

Either all succeed or all fail

ACID principle: ensure data security

ACID: atomicity, consistency, isolation and persistence

Open transaction
 Transaction commit commit()
Transaction rollback rollback()
Close transaction

transfer accounts
A:  1000
B: 1000
A ---------->B
A(900) ---100---> B(1100)

Junit unit test

<!--unit testing -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>

Simple use

@The Test annotation is only valid for methods. As long as the annotated method is added, it can be run directly

@Test
public void c() {
    System.out.println("Hello")
}

Build an environment test

Create a new table

CREATE TABLE account(
	id INT PRIMARY KEY auto_increment,
	`name` varchar(40),
	money FLOAT
);

INSERT INTO account(`name`,money) VALUES('A',1000);
INSERT INTO account(`name`,money) VALUES('B',1000);

Simple test

package com.si.test;

import org.junit.Test;

import java.sql.*;

public class TestJDBC {
    @Test
    public void Test() {
        String url = "jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&useUnicode=true&useSSL=true&timeZone=utc";
        String username = "root";
        String password = "123456";
        Connection connection = null;
        try {
            //1. Load driver class
            Class.forName("com.mysql.cj.jdbc.Driver");
            //2. Connect to the database to represent the database
            connection = DriverManager.getConnection(url, username, password);
            //3. Notify the database to start the transaction false start true close
            connection.setAutoCommit(false);

            String sql1 = "update account set money = money - 100 where name = 'A'";
            connection.prepareStatement(sql1).executeUpdate();

            //Manufacturing error
            // int i = 1/0;
            String sql2 = "update account set money = money + 100 where name = 'B'";
            connection.prepareStatement(sql2).executeUpdate();

            // Commit transaction
            connection.commit();
            System.out.println("Submitted successfully!");
        } catch (Exception throwables) {

            //Notify the database to roll back the transaction when an exception occurs
            try {
                connection.rollback();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            throwables.printStackTrace();
        } finally {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

Keywords: Java Front-end Tomcat

Added by Tokunbo on Wed, 26 Jan 2022 01:20:47 +0200

Programming VIP

Java Web foundation of full stack learning

1. Basic concepts

1.1 Preface

1.2. web application

1.3. Static web

1.4 dynamic web

2. web server

2.1 three technologies

2.2. web server

3,Tomcat

3.1. Installing Tomcat

3.2. Tomcat startup

3.3. Tomcat configuration

3.4. Publish a web site

4,http

4.1. What is http

4.2 two times of http

4.3 http request

Request line

Message header

4.4 http response

Responder

Response status code

5,Maven

5.1 Maven architecture management tool

5.2 Maven Download

5.3. Configure environment variables

5.4 Alibaba cloud image

5.5. Establish local warehouse

5.6. Use Maven in idea

5.7. Create a common maven project

5.8. Mark folder function in idea

5.9. Configure Tomcat in idea

5.10 pom documents

5.11. idea operation directory tree

5.12 use of Maven repository

6,Servlet

6.1 introduction to servlet

6.2,HelloServlet

6.3 principle of Servlet

6.4,Mapping

6.5,ServletContext

6.51. Shared data

6.52. Get initialization parameters

6.53 request forwarding

6.54. Read resource files

6.6,(HttpServlet)Request

6.61. Obtain the information transmitted by the front end and forward the request

6.7,(HttpServlet)Response

6.71 simple classification

6.72 downloading files

6.73 verification code function

6.74 redirection

7,Session,Cookie

7.1 conversation

7.2. Two techniques for saving sessions

7.3,Cookie

7.4. Session (key)

8,JSP

8.1. What is JSP

8.2 JSP principle

8.3. JSP basic syntax

JSP expression

JSP script fragment

Re implementation of script fragments

JSP declaration

8.4. JSP instruction

Custom error page

Extract public pages

8.5 and 9 built-in objects

8.6. JSP tag, JSTL tag, EL expression

EL expression ${}

JSP tag

JSTL expression

9,JavaBean

10. MVC three-tier architecture

10.1. What is MVC

10.2 three tier architecture

11. Filter (important)