jsp的本质

jsp的本质就是servlet，使用过tomcat部署过javaweb项目，都知道在work目录生成jsp页面对应的sevlet。
servlet的本质就是封装了socket

jsp页面

<%--
  Created by IntelliJ IDEA.
  User: wy
  Date: 2019/11/26
  Time: 下午11:21
  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">登录</a>
</body>
</html>

对应的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\">登录</a>\n");
      out.write("</body>\n");
      out.write("</html>\n");
    } catch (java.lang.Throwable t) {
      .....
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

SpringBoot中使用jsp

springboot默认不支持jsp的，要让springboot支持jsp需要引入以下依赖

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

完整的依赖如下：

<?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>

编写测试程序

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;
    }
}

在maven项目中创建webapp文件夹，创建index.jsp文件，访问http://localhost:8080/hello

现在我们在`springboot`中使用了jsp的视图解析器，那么生成的jsp文件在哪里？

这里可以确定的是，只要使用jsp作为视图必定是要生成相应的servlet文件。
在linux系统中，jsp生成的servlet页面在/tmp文件中

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