html element
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>html element</title> <link rel="stylesheet" type="text/css" href="./css/demo.css" /> <script src="./js/demo.js"></script> </head> <body> </body> </html>
Script Elements
Declaration
<%! Code Content %>
//<%!%> You can declare methods, properties, global variables
<%!
//JSP declaration fragment: Note that defining variables or methods on JSP pages is not recommended, just not recommended
int i = 10;
String name = "Vis.Yang";
public void printName(){
System.out.println(name);
}
%>
//Note: Compliance with Java Notes
Expression
<%= Expression %> //Call declared/defined methods or display declared/defined parameter (variable) values Current time: <%= new java.util.Date() %> //Semicolon not allowed after
Scripts (Scriplets)
<% Program code, one or more lines %>
// Local variables or calling methods can be defined in <%%>, but methods cannot be defined.
<%
for (int i=0;i<10,i++) {
...
...
}
%>
//example
<%if(percent < 0.5) { %>
<jsp:forward page="forward.html"/>
<%
}else {
%>
<jsp:forward page="forward.jsp"/>
<% } %>
// Multiple brackets {} need to be wrapped in <%> or it will not work
Instruction Element
<%@ Instruction Name Properties="value" %>
<%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %
<-- Specify the error page path --> <%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" errorPage="error.jsp" %
<-- Set current page as error handling page --> <%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" isErrorPage="true" %
<-- prefix prefix="mytag" Path to Custom Label uri="/WEB-INF/helloSimpleTag.tld"--> <%@ taglib prefix="mytag" uri="/WEB-INF/helloSimpleTag.tld"%> <-- Usage method --> <mytag:helloworld /> <-- Label Reuse -->
Be careful
If an instruction has multiple attributes, it can be written in one instruction, separated by spaces, or in several instructions.
Attribute values are typically enclosed in double or single quotes, and attribute names are case sensitive
Common Instructions
page directive
Used to set properties related to JSP pages, such as reference packages, encoding, error information, etc.
include directive
Used to insert included files at JSP compilation time, such as html, text, or Jsp pages
taglib directive
Used to declare that page users are allowed to customize Tags
page directive
| attribute | describe |
|---|---|
| language | The scripting language to use when writing Jsp pages, defaulting to Java |
| pageEncoding | Specifies the character encoding for Jsp pages, defaulting to ISO-8859-1 commonly used page Encoding="UTF-8" |
| contentType | The MIME type of the response from which the client browser determines the document type, defaulting to "text/html" |
| import | Used to introduce a system or custom package or class on a Jsp page that can be used multiple times or separated by commas |
| session | Used to set the availability of Jsp page session objects, defaulting to true |
| errorPage | Specify an error page and set the value to the Url of the error page |
| isErrorPage | Specifies whether to treat the current page as a Jsp error page, defaulting to false |
include directive
<-- body Embed the specified page inside the label date.jsp --> <-- Page Insertion Role:Extract Public Pages/content --> <%@ include file="date.jsp" %>
Action Elements
<jsp:include page="date.jsp"> <-- Result Insertion -->
<jsp:param name="Vis.Yang" age="3"/> <-- Ginseng -->
</jsp:include>
<jsp:include page="date.jsp"/> <-- No ginseng -->
<jsp:include page="demo.html" flush="true"/>
<--
Introducing results
-->
<jsp:forward page="forward.jsp"/> <-- No ginseng -->
<jsp:forward page="forward.jsp"> <-- page="forward.jsp":Pages to Turn to -->
<jsp:param name="Vis.Yang" age="3"/> <-- Ginseng -->
</jsp:forward>
<--
Forward the client's current request to another Web Resources (to process requests)
Can be HTML Page, JSP Page, Servlet etc.
Address bar unchanged, content of new page
-->
Tip: No intersection between elements
JavaBean
<-- A class name was created Student Of stu1 object -->
<jsp:useBean id="stu1" class="com.my.bean.Student" scope="Scope of action"></jsp:useBean>
<jsp:useBean id="stu2" class="com.my.bean.Student" scope="Scope of action"></jsp:useBean>
<-- scope="Scope of action" page request session application -->
<-- page:Current page is valid request:One request is valid session:Browser remains active until closed application:The server is always there -->
<-- Equivalent to -->
<%
Student stu1=new Student();
Student stu2=new Student();
%>
<-- Get properties and display them to jsp in -->
<jsp:getProperty name="stu1" property="name"></jsp:getProperty>
<jsp:getProperty name="stu2" property="name"></jsp:getProperty>
<-- Equivalent to -->
<%=stu1.name()%>
<%=stu2.name()%>
<-- set a property-->
<jsp:setProperty name="stu1" property="name" value="Vis.Yang"></jsp:setProperty>
<-- Equivalent to -->
<%
stu1.setName("Vis.Yang");
%>
<-- Automatically load all type values of the form into the object property="*" -->
<jsp:setProperty name="stu1" property="*"></jsp:setProperty>
<-- premise:Form name and bean Property names are identical -->
<input type="text" name="name" />
<input type="password" name="pwd" />
<-- Autoload only name Attribute Value property="name" -->
<jsp:setProperty name="stu1" property="name"></jsp:setProperty>
Jsp built-in objects
Built-in objects: objects that can be used directly without being declared or created
| Built-in Objects | function | Range |
|---|---|---|
| request | Requests that trigger service calls | request |
| response | Response to Request | page |
| session | session object created for the requested client | page |
| application | getServletConfig.getContext | session |
| out | Object that writes to the output stream | application |
| exception | Exception handling information | page |
| pagecontext | Page context for this JSP | page |
| page | Implement an instance of the class that handles the current request for this page, as in Java | page |
| config | ServletConfig configuration information for this JSP, web.xml specification | page |
request
The request object encapsulates the client's request information and can be used to obtain the client's request information
Valid within one request, scoped to request
Frequently used to obtain data for forms, common forms are:
Single-line text box, multi-line text box, drop-down menu, radio button, check box, etc.
//common method String getParameter(String name) //Returns the parameter value of the name specified parameter String[] getParameterValues(String name) //Returns an array containing all the values of the parameter name
response
Respond to requests
<%
response.sendRedirect('sucess.jsp'); //Redirect to another page, browser address change, different from jsp:forward
response.addCookie(); //Add cookie s
response.getWriter().println(""); //Equals out.println('');
%>
out
The out object manages the output buffer on the application server, representing the output stream of the JSP page, which is javax. Servlet. Jsp. Instance of JspWriter.
Output data in various formats to the client, typically the content of the object to the browser is text-based
Scope is page, and there is an out object for each JSP page
<%
//Simple Print Output to Browser Page
out.print('');
out.println('');
%>
exception
Exception thrown by JSP engine when executing code
Is java. Instances of the lang.Throwable class
Only on error pages, isErrorPage="true" must be specified in the page directive
//statement
<%!
System.out.println(exception.getMessage()); //console output to IDE
%>
//Script
<%
//Output Exception
out.print(exception.getMessage());//Output to Page
//Page Wrap
out.println("<br>")
System.out.println(exception.getMessage());//console output to IDE
%>
//Expression
<%=exception.getMessage()%> //Output to Page
session
The session object encapsulates all the information belonging to the client session
Open a browser from a client and connect to the server Start until the client closes the browser Leave this server End is called a session
String getId(); //Gets the unique ID set by the JSP engine for session when it is created boolean isNew(); //Determine if this is a new session //Transfer parameters in different pages void setAttribute(String name,Object obj);//Setting parameters Object getAttribute(String name) //Take Parameters void removeAtribute(String name) //Delete parameters Enumeration getAttributeNames() //Returns each property object stored in the session object, resulting in an enumeration type. Multiple parameters void invalidate();cancel session Object, and completely delete the object's contents void setMaxInactiveInterval()Set maximum session Inactive time, if negative, never times out. int getMaxInactiveInterval()Get Maximum session Inactive time long getCreationTime()//Get session creation time long getLastAccessedTime()Obtain session The last time an object was operated on
application
When the server starts, an application object is automatically generated until the server shuts down.
The application lifecycle is the period from server startup to shutdown to enable data sharing among multiple clients. Wider scope than session
The application object is responsible for providing some global information about the application as it runs in the server.
void setAttribute(String name, Object object); //Set properties, specify property names and property values. String getAttribute(String name); //Gets the property value based on the property name. Enumeration getAttributeNames(); //Gets all property names. void removeAttribute(String name); //Delete the corresponding property according to the property name. String getServletInfo(); //Get version information for the current Web server. String getInitParameter(String name); //Gets the initialization parameter value based on the initialization parameter name. int getMajorVersion(); //Gets the major version number of the Servlet API. int getMinorVersion(); //Gets the minor version number of the Servlet API. void log(String message)//Write information to the log file.
The difference between the two
Stored data
session stores individual data for different users
application stores data that is shared between different users
Life Cycle
session from client's first access to server until browser is closed
application starts from server until server shuts down
Example
//Site Visits Statistics
<%>
//First access data is empty
Object obj=session.getAttribute("count");
//User First Access
if(obj==null){
session.setAttribute("count",1);
}else{
Integer num=(Integer)obj;
session.setAttribute("count",++num);
}
}
<%>
The number of times you visit this website:<%=session.getAttribute("count")%>
application Statistics More Recommended
<--When accessed in different browsers,Counters do not accumulate continuously-->
<%>
//First access data is empty
Object obj=application.getAttribute("count");
//User First Access
if(obj==null){
application.setAttribute("count",1);
}else{
Integer num=(Integer)obj;
application.setAttribute("count",++num);
}
}
<%>
The number of times you visit this website:<%=application.getAttribute("count")%>
exception
//common method exception.getMessage(); exception.toString(); <%=exception.toString()%> //Show exceptions //The current page needs to be set to error handling page isErrorPage="true" before use <-- Set current page as error handling page --> <%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" isErrorPage="true" %
request response session application shared data out Output data to browser page exception Handle Exceptions
${pageContext.request.contextPath} Obtain web Resource Path
Roaming Query
ResultSet.TYPE_FORWARD_ONLY //Only scroll forward ResultSet.TYPE_SCROLL_INSENSITIVE //Scroll in both directions, but do not update in time, even if the database's data has been modified and is not reflected in the ResultSet ResultSet.TYPE_SCROLL_SENSITIVE //Scroll in both directions and keep track of database updates to change data in ResultSet ResultSet.CONCUR_READ_ONLY //Default, or show declaration specifying that ResultSet cannot be updated ResultSet.CONCUR_UPDATABLE //Specify that ResultSet can be updated // Statement statement=con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY );
common method
void last();//Go to the last line int getRow();//Get the current row