JavaWeb---总结(十四)JSP原理

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<h2>一、什么是JSP？</h2>
　　JSP全称是Java Server Pages，它和servle技术一样，都是SUN公司定义的一种用于开发动态web资源的技术。 　　JSP这门技术的最大的特点在于，写jsp就像在写html，但它相比html而言，html只能为用户提供静态数据，而Jsp技术允许在页面中嵌套java代码，为用户提供动态数据。
<h2>二、JSP原理</h2>
<h3>2.1、Web服务器是如何调用并执行一个jsp页面的？</h3>
　　浏览器向服务器发请求，不管访问的是什么资源，其实都是在访问Servlet，所以当访问一个jsp页面时，其实也是在访问一个Servlet，服务器在执行jsp的时候，首先把jsp翻译成一个Servlet，所以我们访问jsp时，其实不是在访问jsp，而是在访问jsp翻译过后的那个Servlet，例如下面的代码：
index.jsp
 
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
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>
 <base href="<%=basePath%>">
 
 <title>First Jsp</title>
 
 </head>
 
 <body>
 <%
 out.print("Hello Jsp");
 %>
 </body>
</html>
当我们通过浏览器访问index.jsp时，服务器首先将index.jsp翻译成一个index_jsp.class，在Tomcat服务器的work\Catalina\localhost\项目名\org\apache\jsp目录下可以看到index_jsp.class的源代码文件index_jsp.java，index_jsp.java的代码如下：
package org.apache.jsp;
 
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.*;
 
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
 implements org.apache.jasper.runtime.JspSourceDependent {
 
 private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();
 
 private static java.util.List _jspx_dependants;
 
 private javax.el.ExpressionFactory _el_expressionfactory;
 private org.apache.AnnotationProcessor _jsp_annotationprocessor;
 
 public Object getDependants() {
 return _jspx_dependants;
 }
 
 public void _jspInit() {
 _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
 _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());
 }
 
 public void _jspDestroy() {
 }
 
 public void _jspService(HttpServletRequest request, HttpServletResponse response)
 throws java.io.IOException, ServletException {
 
 PageContext pageContext = null;
 HttpSession session = null;
 ServletContext application = null;
 ServletConfig config = null;
 JspWriter out = null;
 Object page = this;
 JspWriter _jspx_out = null;
 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');
 out.write('\n');
 
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 
 out.write("\r\n");
 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("

JavaWeb---总结(十四)JSP原理

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