JSP系列教材 (二)- 转译为Servlet

 

为什么JSP可以在html中运行java代码? 这是因为JSP被转译成了Servlet

步骤1:执行过程
步骤2:hello_jsp.java 为什么是Servlet

步骤 1 : 执行过程

1. 把 hello.jsp转译为hello_jsp.java
2. hello_jsp.java 位于
d: omcatworkCatalinalocalhost\_orgapachejsp
3. hello_jsp.java是一个servlet
4. 把hello_jsp.java 编译为hello_jsp.class
5. 执行hello_jsp,生成html
6. 通过http协议把html 响应返回给浏览器

执行过程

步骤 2 : hello_jsp.java 为什么是Servlet

Servlet章节中,我们说HelloServlet是一个Servlet,不是因为它的类名里有一个"Servlet",而是因为它继承了 HttpServlet

打开转译hello.jsp 后得到的hello_jsp.java,可以发现它继承了类
(D: omcatworkCatalinalocalhost\_orgapachejsphello_jsp.java)

org.apache.jasper.runtime.HttpJspBase


而HttpJspBase 继承了HttpServlet

所以我们说hello_.jsp.java 是一个Servlet

/*

 * Generated by the Jasper component of Apache Tomcat

 * Version: Apache Tomcat/7.0.64

 * Generated at: 2017-01-07 01:45:17 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.*;

import java.util.*;

public final class hello_jsp extends org.apache.jasper.runtime.HttpJspBase

    implements org.apache.jasper.runtime.JspSourceDependent {

  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 javax.el.ExpressionFactory _el_expressionfactory;

  private org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {

    return _jspx_dependants;

  }

  public void _jspInit() {

    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();

    _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());

  }

  public void _jspDestroy() {

  }

  public void _jspService(final javax.servlet.http.HttpServletRequest request, finaljavax.servlet.http.HttpServletResponse response)

        throws java.io.IOException, javax.servlet.ServletException {

    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,

                nulltrue8192true);

      _jspx_page_context = pageContext;

      application = pageContext.getServletContext();

      config = pageContext.getServletConfig();

      session = pageContext.getSession();

      out = pageContext.getOut();

      _jspx_out = out;

      out.write(" ");

      out.write(" ");

      out.write("你好 JSP ");

      out.write(" ");

      out.write("<br> ");

      out.write(" ");

      out.print(new Date().toLocaleString());

    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);

    }

  }

}


更多内容,点击了解: https://how2j.cn/k/jsp/jsp-transfer/574.html

原文地址:https://www.cnblogs.com/Lanht/p/12615392.html