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Servlet+JSP例子

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12/01
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前面两节已经学习了什么是Servlet,Servlet接口函数是哪些、怎么运行、Servlet生命周期是什么?  以及Servlet中的模式匹配URL，web.xml配置和HttpServlet。怎么在Eclipse中新建一个Servlet工程项目。 今天这里主要是创建一个Servlet+JSP的例子。

一、学习之前补充一下web.xml中配置问题

web.xml中<welcome-file-list>配置（（web欢迎页、首页））

用于当用户在url中输入工程名称或者输入web容器url（如http://localhost:8080/）时直接跳转的页面.

welcome-file-list的工作原理是，按照welcome-file的.list一个一个去检查是否web目录下面存在这个文件，如果存在，继续下面的工作（或者跳转到index.html页面，或者配置有struts的，会直接struts的过滤工作）.如上例，先去webcontent(这里是Eclipse的工程目录根目录)下是否真的存在index.html这个文件，如果不存在去找是否存在index.jsp这个文件，以此类推。

还要说的是welcome-file不一定是html或者jsp等文件，也可以是直接访问一个action。就像我上面配置的一样，但要注意的是，一定要在webcontent下面建立一个index.action的空文件，然后使用struts配置去跳转，不然web找不到index.action这个文件，会报404错误，

如果配置了servlet的url-pattern是/*，那么访问localhost:8080/会匹配到该servlet上，而不是匹配welcome-file-list；如果url-pattern是/（该servlet即为默认servlet），如果其他匹配模式都没有匹配到，则会匹配welcome-file-list。

例如：

FirstServlet.java 

 package servlet;

 import java.io.IOException;

 import java.io.PrintWriter;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 //@WebServlet("/Firstservlet")

 public class FirstServlet extends HttpServlet {

     /* (non-Javadoc)

      * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)

      */

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         System.out.println("处理get()的请求。。。");

         PrintWriter pw = resp.getWriter();

         pw.write("hello!");

     }

     /* (non-Javadoc)

      * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)

      */

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

     }

 }

web.xml 配置 

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

   <display-name>ServletTest</display-name>

   <welcome-file-list>

     <welcome-file>index.html</welcome-file>

     <welcome-file>index.htm</welcome-file>

     <welcome-file>index.jsp</welcome-file>

     <welcome-file>default.html</welcome-file>

     <welcome-file>default.htm</welcome-file>

     <welcome-file>default.jsp</welcome-file>

   </welcome-file-list>

   <servlet><servlet-name>ServletTest</servlet-name>

   <servlet-class>servlet.FirstServlet</servlet-class>

   </servlet>

   <servlet-mapping>

       <servlet-name>ServletTest</servlet-name>

       <url-pattern>/*</url-pattern>

   </servlet-mapping>

 </web-app>

index.jsp 

 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"

     pageEncoding="ISO-8859-1"%>

 <!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=ISO-8859-1">

 <title>Insert title here</title>

 </head>

 <body>

 <a href = "/ServletTest/FirstServlet">get this first servlet</a>

 </body>

 </html>

如果在上面web.xml里面配置<url-pattern>/*</url-pattern>， 在浏览器输入：直接匹配到Servlet

如果在上面web.xml里面配置<url-pattern>/</url-pattern>， 在浏览器输入：可以看出匹配到index.jsp

正常在web.xml里面配置<url-pattern>/FirstServlet</url-pattern>，会先匹配到index.jsp

二、Servlet+JSP

直接加例子： 

 package com.ht.servlet;

 public class AccountBean {

     private String username;

     private String password;

     /**

      * @return the username

      */

     public String getUsername() {

         return username;

     }

     /**

      * @param username the username to set

      */

     public void setUsername(String username) {

         this.username = username;

     }

     /**

      * @return the password

      */

     public String getPassword() {

         return password;

     }

     /**

      * @param password the password to set

      */

     public void setPassword(String password) {

         this.password = password;

     }

 }

 package com.ht.servlet;

 import java.io.IOException;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import javax.servlet.http.HttpSession;

 /**

  * Servlet implementation class AccountBean

  */

 @WebServlet("/CheckAccount")

 public class CheckAccount extends HttpServlet {

     private static final long serialVersionUID = 1L;

     /**

      * @see HttpServlet#HttpServlet()

      */

     public CheckAccount() {

         super();

         // TODO Auto-generated constructor stub

     }

     /**

      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

      */

     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         HttpSession sessionzxl = request.getSession();

         AccountBean account = new AccountBean();

         String username = request.getParameter("username");

         String pwd = request.getParameter("pwd");

         account.setPassword(pwd);

         account.setUsername(username);

         System.out.println("username :"+ username + " password :" + pwd);

         if((username != null)&&(username.trim().equals("jspp"))) {

             System.out.println("username is right!");

                if((pwd != null)&&(pwd.trim().equals("1"))) {

                    System.out.println("success");

                    sessionzxl.setAttribute("account", account);

                    String login_suc = "success.jsp";

                    response.sendRedirect(login_suc);

                    return;

                }

         }

         System.out.println("fail!");

         String login_fail = "fail.jsp";

         response.sendRedirect(login_fail);

         return;

     }

     /**

      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

      */

     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         doGet(request, response);

     }

 }

登录的jsp页面如下Login.jsp 

 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"

     pageEncoding="UTF-8"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <%

 String path = request.getContextPath();

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

 %>

 <html>

 <head>

 <base href="<%=basePath%>">

 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

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

 </head>

 <body>

     This is my JSP page. <br>

     <form action="login">

     username:<input type="text" name="username"><br>

     password:<input type="password" name="pwd"><br>

     <input type="submit" value="Submit">

     </form>

 </body>

 </html>

登录成功界面如下success.jsp： 

 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"

     pageEncoding="UTF-8"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <%@ page import="com.ht.servlet.AccountBean"%>

 <%

 String path = request.getContextPath();

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

 %>

 <html>

 <head>

 <base href="<%=basePath%>">

 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

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

 </head>

 <body>

 <%AccountBean account = (AccountBean)session.getAttribute("account");%>

 username:<%= account.getUsername()%> <br>

 password:<%= account.getPassword() %> <br>

 basePath: <%=basePath%><br>

 path:<%=path%><br>

 </body>

 </html>

登录失败的jsp页面如下：fail.jsp 

 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"

     pageEncoding="UTF-8"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <%

 String path = request.getContextPath();

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

 %>

 <html>

 <head>

 <base href="<%=basePath%>">

 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

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

 </head>

 <body>

     Login Failed! <br>

     basePath: <%=basePath%><br>

     path:<%=path%><br>

 </body>

 </html>

web.xml配置如下： 

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

   <display-name>ServletTest</display-name>

   <welcome-file-list>

     <welcome-file>Login.jsp</welcome-file>

   </welcome-file-list>

   <servlet>

        <description>This is the description of my J2EE component</description>

        <display-name>This is the display name of my J2EE component</display-name>

     <servlet-name>CheckAccount</servlet-name>

     <servlet-class>com.ht.servlet.CheckAccount</servlet-class>

   </servlet>

   <servlet-mapping>

     <servlet-name>CheckAccount</servlet-name>

     <url-pattern>/login</url-pattern>

   </servlet-mapping>

 </web-app>

描述一下上面运行过程：

在浏览器输入：http://localhost:8080/ServletTest/     会通过欢迎页面welcome-file-list找到登录页面Login.jsp, 界面显示如下：

在登录页面输入用户名和密码，点击登录，找到对应的action, 会去运行/login其对应的servlet, 找到doGet()方法，判断用户名和密码

如果用户名密码不是jspp和1，就会跳转到失败页面fail.jsp

如果用户名等于jspp和1，则跳转到成功页面success.jsp

Session

上面就是一个最简单的JSP和servlet例子。在运行上面例子中，有一个概念session.

在checkAccount.java中，直接通过request获取session

HttpSession sessionzxl = request.getSession();

后面将定义的变量存储到session中：sessionzxl.setAttribute("account", account);

在jsp中怎么获取session？

在success.jsp中，有这么一行<%AccountBean account = (AccountBean)session.getAttribute("account");%>，那么session来至于哪儿？

查看资料后得知，session是jsp隐式对象。

JSP隐式对象是JSP容器为每个页面提供的Java对象，开发者可以直接使用它们而不用显式声明。JSP隐式对象也被称为预定义变量。

JSP所支持的九大隐式对象：

对象 描述
request HttpServletRequest 接口的实例
response HttpServletResponse 接口的实例
out JspWriter 类的实例，用于把结果输出至网页上
session HttpSession 类的实例
application ServletContext 类的实例，与应用上下文有关
config ServletConfig 类的实例
pageContext PageContext 类的实例，提供对JSP页面所有对象以及命名空间的访问
page 类似于Java类中的this关键字
Exception Exception 类的对象，代表发生错误的JSP页面中对应的异常对象 
    session是jsp的内置对象，所以你可以直接写在jsp的

    <%

    session.setAttribute("a",  b);  //把b放到session里，命名为a，

    String M = session.getAttribute(“a”).toString(); //从session里把a拿出来，并赋值给M

    %>

下节添加一个Servlet+jsp+SQL例子。

https://blog.csdn.net/superit401/article/details/51974409

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