JSP页面生命周期

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一 JSP页面生命周期图

二生命周期解释

三实战

1、创建JspLifeCycleDemo项目

2、编写index.jsp文件

<%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8"%>

<%@ page import="java.text.*" %>

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

<title>My JSP 'index.jsp' starting page</title>

<!--

-->

</head>

<body>

<h1>JSP生命周期</h1>

<hr>

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");

String s = sdf.format(new Date());

今天是：<%=s %>

</body>

</html>

四运行结果

五运行说明

1、当Tomcat首次启动时，D:\apache-tomcat-7.0.81\work\Catalina\localhost\JspLifeCycleDemo目录为空，因为还没有收到任何请求。

2、当JSP页面首次请求时，在D:\apache-tomcat-7.0.81\work\Catalina\localhost\JspLifeCycleDemo\org\apache\jsp目录下会生成对于的Java文件和字节码文件。

其中：_jspInit函数在整个生命周期只运行一次。

_jspService函数每次请求都会运行。

* Generated by the Jasper component of Apache Tomcat

* Version: Apache Tomcat/7.0.81

* Generated at: 2017-09-16 06:54:10 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.*;

import java.text.*;

public final class index_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 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 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 {

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");

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

out.write("\r\n");

out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n");

out.write("<html>\r\n");

out.write(" <head>\r\n");

out.write(" <base href=\"");

out.print(basePath);

out.write("\">\r\n");

out.write(" \r\n");

out.write(" <title>My JSP 'index.jsp' starting page</title>\r\n");

out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n");

out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n");

out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n");

out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n");

out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n");

out.write("\t<!--\r\n");

out.write("\t<link rel=\"stylesheet\" type=\"text/css\" href=\"styles.css\">\r\n");

out.write("\t-->\r\n");

out.write(" </head>\r\n");

out.write(" \r\n");

out.write(" <body>\r\n");

out.write(" <h1>JSP生命周期</h1>\r\n");

out.write(" <hr>\r\n");

out.write(" ");

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");

String s = sdf.format(new Date());

out.write("\r\n");

out.write(" 今天是：");

out.print(s );

out.write("\r\n");

out.write(" </body>\r\n");

out.write("</html>\r\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);

}

3、如果JSP页面修改了，JSP引擎会重新编译JSP页面，再重新生成新的字节码文件。

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