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！