javaWEB总结(11):JSP简介及原理

来源：互联网发布：代谢综合征基因组数据编辑：程序博客网时间：2024/05/20 01:47

前言

本文主要通过一个简单小例子，介绍JSP的原理。

1.项目结构

2.web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">    <display-name>javaWeb_09</display-name>    <welcome-file-list>        <welcome-file>login.jsp</welcome-file>    </welcome-file-list></web-app>

3.login.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>my first jsp</title></head><body><% out.write("Hello World") ;%></body></html>

4.运行后页面显示

5.打开eclipse的workspace,

找到类似于下面的地址:

D:\Users\Administrator\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp10\work\Catalina\localhost\javaWeb_11\org\apache\jsp

我们看到有一个login_jsp.java文件，打开它。

6.login_jsp.java

login_jsp继承了HttpJspBase,实现了JspSourceDependent接口，里面有类似于servlet的_JspInit(),_JspDestroy等方法。

/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/7.0.54 * Generated at: 2016-11-26 07:51:43 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 login_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, final javax.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,      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("\r\n");      out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");      out.write("<html>\r\n");      out.write("<head>\r\n");      out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=ISO-8859-1\">\r\n");      out.write("<title>my first jsp</title>\r\n");      out.write("</head>\r\n");      out.write("<body>\r\n");      out.write("\t"); out.write("Hello World") ;      out.write("\r\n");      out.write("</body>\r\n");      out.write("</html>");    } catch (java.lang.Throwable t) {      if (!(t instanceof javax.servlet.jsp.SkipPageException)){        out = _jspx_out;        if (out != null && out.getBufferSize() != 0)          try { 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);    }  }}

7.ctrl+shift+t找到HttpJspBase的源码

8.HttpJspBase

很明显HttpJspBase继承了HttpServlet实现了HttpJspPage接口

/*    */ package org.apache.jasper.runtime;/*    */ /*    */ import java.io.IOException;/*    */ import javax.servlet.ServletConfig;/*    */ import javax.servlet.ServletException;/*    */ import javax.servlet.http.HttpServlet;/*    */ import javax.servlet.http.HttpServletRequest;/*    */ import javax.servlet.http.HttpServletResponse;/*    */ import javax.servlet.jsp.HttpJspPage;/*    */ import org.apache.jasper.compiler.Localizer;/*    */ /*    */ public abstract class HttpJspBase/*    */   extends HttpServlet/*    */   implements HttpJspPage/*    */ {/*    */   private static final long serialVersionUID = 1L;/*    */   /*    */   public final void init(ServletConfig config)/*    */     throws ServletException/*    */   {/* 47 */     super.init(config);/* 48 */     jspInit();/* 49 */     _jspInit();/*    */   }/*    */   /*    */   public String getServletInfo()/*    */   {/* 54 */     return Localizer.getMessage("jsp.engine.info");/*    */   }/*    */   /*    */   public final void destroy()/*    */   {/* 59 */     jspDestroy();/* 60 */     _jspDestroy();/*    */   }/*    */   /*    */ /*    */ /*    */ /*    */ /*    */   public final void service(HttpServletRequest request, HttpServletResponse response)/*    */     throws ServletException, IOException/*    */   {/* 70 */     _jspService(request, response);/*    */   }/*    */   /*    */   public void jspInit() {}/*    */   /*    */   public void _jspInit() {}/*    */   /*    */   public void jspDestroy() {}/*    */   /*    */   protected void _jspDestroy() {}/*    */   /*    */   public abstract void _jspService(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse)/*    */     throws ServletException, IOException;/*    */ }

总结

(1)JSP是简化Servlet编写的一种技术，它将Java代码和HTML语句混合在同一个文件中编写，只对网页中的要动态产生的内容采用Java代码来编写，而对固定不变的静态内容采用普通静态HTML页面的方式编写。

(2)新建一个jsp页面，在<% %>中即可编写java代码。

(3)jsp可以放在web应用程序中除了WEB-INF及其子目录以外的其他任何目录中。

(4)JSP运行原理:JSP本质上是一个servlet，每个JSP在第一次被访问时，JSP引擎将它翻译成一个servlet源程序，接着再把servlet源程序翻译成servlet的class类文件，然后由web容器(Servlet引擎)像调用普通Servlet一样来装载和解释执行这个由JSP页面翻译成的Servlet程序。

附

参考视频:点击打开链接

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