JSP页面最终是编译为Servlet执行的

JSP页面最终是编译为Servlet执行的，你可以在Tomcat的%CATALINA_HOME%/work/Catalina/localhost中找到一个文件夹，该文件夹跟你的web-project的虚拟路径一致！比如说，我在%CATALINA_HOME%/conf/server.xml中配置了我的web-project为如下

<Context path="/mldn" docBase="E:/web.workspace/mldndemo/WebContent" reloadable="true"/>

那么在%CATALINA_HOME%/work/Catalina/localhost中就有一个文件夹名为“mldn”！

并且，你在\mldn\org\apache\jsp目录下还会找到你所有jsp页面对应的.class文件，这就证明了JSP页面最终是编译为Servlet执行的！

所以，本质上一个JSP页面对应一个Servlet！

因此，看到web.xml如下的配置，不要奇怪！因为JSP本质上就是Servlet！你看看JSP页面的代码，我们完全可以将其写为Servlet！

web.xml

    <servlet>
        <servlet-name>dbinit</servlet-name>
        <jsp-file>/WEB-INF/init.jsp</jsp-file>
        <init-param>
            <param-name>driver</param-name>
            <param-value>org.gjt.mm.mysql.Driver</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/mldn</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>dbinit</servlet-name>
        <url-pattern>/config.mldn</url-pattern>
    </servlet-mapping>

init.jsp（输入http://127.0.0.1:8080/mldn/config.mldn访问）

<%@ 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=UTF-8">
<title>MLDN</title>
</head>
<body>
<%
    String dbDriver = config.getInitParameter("driver");
    String dbURL = config.getInitParameter("url");
%>
<h3>驱动程序：<%=dbDriver %></h3>
<h3>链接地址：<%=dbURL %></h3>
</body>
</html>

等价的Servlet：

package org.lxh.servletdemo;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DBInitServlet extends HttpServlet {
    private String dbDriver = null, dbURL = null;
    @Override
    public void init(ServletConfig config) throws ServletException {
        // Javadoc: When overriding this form of the method, call super.init(config). 
        super.init(config);
        this.dbDriver = config.getInitParameter("driver");
        this.dbURL = config.getInitParameter("url");
    }
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.println("<h3>驱动程序：" + dbDriver + "</h3>");
        writer.println("<h3>链接地址：" + dbURL + "</h3>");
    }
    
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException {
        this.doGet(req, resp);
    }
}

 

该Servlet的配置

<!-- DBInitServlet -->
    <servlet>
        <servlet-name>dbInitServlet</servlet-name>
        <servlet-class>
            org.lxh.servletdemo.DBInitServlet
        </servlet-class>
        <init-param>
            <param-name>driver</param-name>
            <param-value>org.gjt.mm.mysql.Driver</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/mldn</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>dbInitServlet</servlet-name>
        <url-pattern>/DBInitServlet</url-pattern>
    </servlet-mapping>

调用该Servlet的页面：

dbinit_info.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=UTF-8">
<title>Insert title here</title>
</head>
<body>
<jsp:forward page="/DBInitServlet"/>
</body>
</html>

这二者显示的结果是一样的！

posted @ 2013-07-09 11:30  rldts  阅读(2157)  评论(0)  编辑  收藏  举报