JSP Servlet 相关理解_为社么说js编译完成后生成servlet-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_43183340/article/details/106123670

Servlet & JSP

一、是什么

JSP (Java Server Pages)

Sun公司出品，用来作为服务器端动态页面技术的组件规范。其为.jsp后缀的文件，主要为html和Java代码。

Servlet (Server Applet)

Sun公司出品，用来扩展Web服务器功能的组件规范，属于服务器程序。其为.java后缀文件，extends HttpServlet的相关类。

通俗理解 JSP：在Html里面写Java Servlet：在Java里面写html代码

二、区别与联系

运行过程
JSP Engin把JSP程序转换为Servlet代码，接着将其编译为类文件,并存储于内存中。故而客户端在第一次请求JSP时较慢，之后就会较快。

访问Servlet，可以直接对其编译好的类文件执行。
使用方式
JSP位置（webapps根目录或者其根目录的子目录下，可以与html放置同一位置）。同时无需配置，直接使用。

Servlet使用，必须将其放置于特定位置而且必须对其映射进行配置。
程序组成
JSP在静态html内容中嵌入Java代码，Java代码被动态执行后生成html内容

Servlet在Java代码中通过HttpServletResponse对象中动态输出html内容
职能分工
JSP 侧重于前端页面显示

Servlet 侧重于页面逻辑
本质关系
JSP 本质上为Servlet，用JSP实现的页面用Servlet也能实现

三、MVC角度理解

在这里插入图片描述
图片processon链接.

四、idea下 Tomcat jsp编译为servlet

其存储路径

C:\Users\xxxxxx.IntelliJIdea2019.3\system\tomcat\Unnamed_servlet\work\Catalina\localhost\servlet_war_exploded\org\apache\jsp

为相关 index.jsp 转为的 index_jsp.java index_jsp.class 文件。此过程由Tomcat操作。

jsp 代码

<%--
  Created by IntelliJ IDEA.
  User: xxxxxxxxxx
  Date: 2020/5/13
  Time: 23:34
  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>
  <form action="<%=request.getContextPath()%>/html" method="GET">
    <input type="submit"value="提交">
  </form>
  $END$
  </body>
</html>

java 代码

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/9.0.34
 * Generated at: 2020-05-14 00:30:29 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {

  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

  private static final java.util.Set<java.lang.String> _jspx_imports_packages;

  private static final java.util.Set<java.lang.String> _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("javax.servlet");
    _jspx_imports_packages.add("javax.servlet.http");
    _jspx_imports_packages.add("javax.servlet.jsp");
    _jspx_imports_classes = null;
  }

  private volatile javax.el.ExpressionFactory _el_expressionfactory;
  private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set<java.lang.String> getPackageImports() {
    return _jspx_imports_packages;
  }

  public java.util.Set<java.lang.String> getClassImports() {
    return _jspx_imports_classes;
  }

  public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
    if (_el_expressionfactory == null) {
      synchronized (this) {
        if (_el_expressionfactory == null) {
          _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
        }
      }
    }
    return _el_expressionfactory;
  }

  public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
    if (_jsp_instancemanager == null) {
      synchronized (this) {
        if (_jsp_instancemanager == null) {
          _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
        }
      }
    }
    return _jsp_instancemanager;
  }

  public void _jspInit() {
  }

  public void _jspDestroy() {
  }

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

    if (!javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      final java.lang.String _jspx_method = request.getMethod();
      if ("OPTIONS".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        return;
      }
      if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
        return;
      }
    }

    final javax.servlet.jsp.PageContext pageContext;
    javax.servlet.http.HttpSession session = null;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    javax.servlet.jsp.JspWriter _jspx_out = null;
    javax.servlet.jsp.PageContext _jspx_page_context = null;


    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("  </head>\n");
      out.write("  <body>\n");
      out.write("  <form action=\"");
      out.print(request.getContextPath());
      out.write("/html\" method=\"GET\">\n");
      out.write("    <input type=\"submit\"value=\"提交\">\n");
      out.write("  </form>\n");
      out.write("  $END$\n");
      out.write("  </body>\n");
      out.write("</html>\n");
    } catch (java.lang.Throwable t) {
      if (!(t instanceof javax.servlet.jsp.SkipPageException)){
        out = _jspx_out;
        if (out != null && out.getBufferSize() != 0)
          try {
            if (response.isCommitted()) {
              out.flush();
            } else {
              out.clearBuffer();
            }
          } catch (java.io.IOException e) {}
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
        else throw new ServletException(t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}