Analysis of the principle of Jsp in Spring Boot

The essence of jsp

The essence of jsp is servlet. You have deployed Java Web project with tomcat, and you know how to generate the corresponding servlet of jsp page in the work directory.
The essence of servlet is to encapsulate socket

jsp page

<%--
  Created by IntelliJ IDEA.
  User: wy
  Date: 2019/11/26
  Time: Afternoon11:21
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h2>Hello</h2>
<a href="login">Sign in</a>
</body>
</html>

Corresponding Servlrt

ublic final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {
                     .......
  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
      throws java.io.IOException, javax.servlet.ServletException {
          .........
    try {
      response.setContentType("text/html;charset=UTF-8");
      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;

      out.write("\n");
      out.write("\n");
      out.write("<html>\n");
      out.write("<head>\n");
      out.write("    <title>Title</title>\n");
      out.write("        111111111111\n");
      out.write("</head>\n");
      out.write("<body>\n");
      out.write("<h2>Hello</h2>\n");
      out.write("<a href=\"login\">Sign in</a>\n");
      out.write("</body>\n");
      out.write("</html>\n");
    } catch (java.lang.Throwable t) {
      .....
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

Using jsp in SpringBoot

Spring boot does not support jsp by default. To make spring boot support jsp, you need to introduce the following dependencies

    <dependency>
        <groupId>org.apache.tomcat.embed</groupId>
        <artifactId>tomcat-embed-jasper</artifactId>
    </dependency>

The complete dependencies are as follows:

<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.4.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>4.0.1</version>
			<scope>provided</scope>
		</dependency>

		<dependency>
			<groupId>org.apache.tomcat.embed</groupId>
			<artifactId>tomcat-embed-jasper</artifactId>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Write test program

package com.example.demo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.view.InternalResourceView;

@Controller
public class HelloController {

    @RequestMapping("/hello")
    public ModelAndView hello(){
        ModelAndView mv = new ModelAndView();
        InternalResourceView internalResourceView = new InternalResourceView("index.jsp");
        mv.setView(internalResourceView);
        return  mv;
    }
}

Create webapp folder in maven project, create index.jsp file, access http://localhost:8080/hello

Now we use the view parser of jsp in springboot, so where is the generated jsp file?

What is certain here is that as long as you use jsp as the view, you must generate the corresponding servlet file.
In linux system, the servlet page generated by jsp is in the / tmp file

├── tomcat.6136740723794350932.8080
│   └── work
│       └── Tomcat
│           └── localhost
│               └── ROOT
│                   └── org
│                       └── apache
│                           └── jsp
│                               ├── index_jsp.class
│                               └── index_jsp.

Note: the corresponding servlet page will be generated only when the corresponding jsp page is visited for the first time