jsp教程上：我们一定学了servlet，也学习了jsp，那么jsp与servlet的区别是什么呢，jsp与servlet又有什么关系呢？下面我们先创建一个demo.jsp的页面，然后tomcat运行，看看jsp编译之后是怎么样的呢？
<%@page import="java.text.SimpleDateFormat"%>
<%@ 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>jsp演示代码</title>
</head>
<body>
<%
SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
out.write("输出当前时间:"+sf.format(new Date()));
%>
</body>
</html>demo.jsp代码运行的结果是：
输出当前时间:2017-02-08 22:09:10
上面的代码已经运行之后，我们再到tomcat服务器的work\Catalina文件夹里面去查看编译后生成的demo_jsp.java这个文件，看看demo.jsp文件被编译之后变成java文件之后是什么样子的。
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.text.SimpleDateFormat;
import java.util.*;
public final class demo_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
//删除了部分代码
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("\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>jsp演示代码</title>\r\n");
out.write(" </head>\r\n");
out.write(" <body>\r\n");
out.write(" ");
SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
out.write("输出当前时间:"+sf.format(new Date()));
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);
}
}
}你会发现上面的demo.jsp文件被编译成了servlet的代码，其实jsp和servlet的区别就是表现形式不一样，本质却是一样的，servlet是完全可以替代这个demo.jsp来输出这个页面,但是为什么又需要jsp呢？
这是因为在实际项目中，jsp有网页标签，适合做网页界面的设计，如果所有的js和css都通过servlet来write输出的话，代码会变得非常繁琐，所以实际项目中servlet主要负责网站后台逻辑的实现，jsp主要负责的是页面的布局和后台数据的获取。
jsp和servlet的关系实际上就是一种互补的关系，只是职责不一样，完整学习jsp教程，请看下一篇：10分钟学会使用jsp内置对象域对象及el表达式