[原创]java WEB学习笔记10：GenericServlet

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1.实现页面的跳转:对于LoginServlet.java 采用直接实现的Servlet接口的方式

web.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 3     xmlns="http://java.sun.com/xml/ns/javaee"
 4     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
 5     id="WebApp_ID" version="3.0">
 6     
 7     <!-- 配置web应用的初始化参数 -->
 8     <context-param>
 9         <param-name>user</param-name>
10         <param-value>jason</param-value>
11     </context-param>
12     
13     <context-param>
14         <param-name>password</param-name>
15         <param-value>zhangzhen</param-value>
16     </context-param>
17     
18     <!-- 配置和映射servlet -->
19     <servlet>
20         <servlet-name>LoginServlet</servlet-name>
21         <servlet-class>com.jason.testweb.LoginServlet</servlet-class>
22     </servlet>
23     
24     <servlet-mapping>
25         <servlet-name>LoginServlet</servlet-name>
26         <url-pattern>/login</url-pattern> <!-- 和提表单提交的 action 一致 -->
27     </servlet-mapping>
28     
29 </web-app>

 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 2 <html>
 3 <head>
 4 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 5 <title>this is a test </title>
 6 </head>
 7 <body>
 8     <form action="login" method="post">
 9     
10         user:<input type="text" name="username"/>
11         password:<input type="text" name="password"/>
12             
13         <input type="submit" value="submit"/>
14         
15     </form>
16 </body>
17 </html>

LoginServlet.java

 1 package com.jason.testweb;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 
 6 import javax.servlet.Servlet;
 7 import javax.servlet.ServletConfig;
 8 import javax.servlet.ServletContext;
 9 import javax.servlet.ServletException;
10 import javax.servlet.ServletRequest;
11 import javax.servlet.ServletResponse;
12 
13 public class LoginServlet implements Servlet {
14 
15     @Override
16     public void destroy() {
17         // TODO Auto-generated method stub
18     }
19 
20     @Override
21     public ServletConfig getServletConfig() {
22         // TODO Auto-generated method stub
23         return null;
24     }
25 
26     @Override
27     public String getServletInfo() {
28         // TODO Auto-generated method stub
29         return null;
30     }
31 
32     private ServletConfig servletConfig; //自定义一个成员变量
33 
34     @Override
35     public void init(ServletConfig servletConfig) throws ServletException {
36 
37         this.servletConfig = servletConfig;
38 
39     }
40 
41     @Override
42     public void service(ServletRequest request, ServletResponse response)
43             throws ServletException, IOException {
44         // 1.获取请求参数
45         String userName = request.getParameter("username");
46         String passWord = request.getParameter("password");
47 
48         // 2.获取当前web 应用的初始化参数，user，password
49         ServletContext servletContext = servletConfig.getServletContext();
50         String initUser = servletContext.getInitParameter("user");
51         String initPassword = servletContext.getInitParameter("password");
52 
53         PrintWriter out = response.getWriter();
54 
55         // 3.比对
56         // 4.打印响应字符串
57         if (initUser.equals(userName) && initPassword.equals(passWord)) {
58             out.print("hello :" + userName);
59         } else {
60             out.print("sorry :" + userName);
61         }
62 
63     }
64 
65 }

2.实现页面的跳转：创建一个MyGenericServlet的类，实现Servlet接口，对于 LoginServlet.java则继承MyGenericServlet类

MyGenericServlet.java

 1 package com.jason.testweb;
 2 
 3 import java.io.IOException;
 4 import java.util.Enumeration;
 5 
 6 import javax.servlet.GenericServlet;
 7 import javax.servlet.Servlet;
 8 import javax.servlet.ServletConfig;
 9 import javax.servlet.ServletContext;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 
14 /**
15  * 
16  * @author:jason
17  * @time:2016年5月18日
18  * @description:自定义的Servlet 接口的实现类，，简化开发
19  *
20  */
21 
22 public abstract class MyGenericServlet implements Servlet {
23 
24     @Override
25     public void destroy() {
26     }
27 
28     @Override
29     public ServletConfig getServletConfig() {
30         return servletConfig;
31     }
32 
33     private ServletConfig servletConfig; // 声明一个成员变量
34 
35     @Override
36     public String getServletInfo() {
37         return null;
38     }
39 
40     @Override
41     public void init(ServletConfig arg0) throws ServletException {
42         this.servletConfig = arg0;
43     }
44 
45     @Override
46     // 声明为抽象方法，由每个继承的类的实现业务
47     public abstract void service(ServletRequest arg0, ServletResponse arg1)
48             throws ServletException, IOException;
49 
50 }

LoginServlet.java

 1 package com.jason.testweb;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 
 6 import javax.servlet.Servlet;
 7 import javax.servlet.ServletConfig;
 8 import javax.servlet.ServletContext;
 9 import javax.servlet.ServletException;
10 import javax.servlet.ServletRequest;
11 import javax.servlet.ServletResponse;
12 
13 public class LoginServlet extends MyGenericServlet {
14 
15     @Override
　　　　　　//重写抽象方法
16     public void service(ServletRequest request, ServletResponse response)
17             throws ServletException, IOException {
18         // 1.获取请求参数
19         String userName = request.getParameter("username");
20         String passWord = request.getParameter("password");
21 
22         // 2.获取当前web 应用的初始化参数，user，password
23         ServletContext servletContext = getServletConfig().getServletContext();
24         String initUser = servletContext.getInitParameter("user");
25         String initPassword = servletContext.getInitParameter("password");
26 
27         PrintWriter out = response.getWriter();
28 
29         // 3.比对
30         // 4.打印响应字符串
31         if (initUser.equals(userName) && initPassword.equals(passWord)) {
32             out.print("hello :" + userName);
33         } else {
34             out.print("sorry :" + userName);
35         }
36 
37     }
38 
39 }

2.关于GenericServlet

　　public abstract class GenericServlet extends java.lang.Object implements Servlet, ServletConfig, java.io.Serializable

1）是一个Servlet。　是Servlet 接口和ServletConfig 接口的实现类。但是是一个抽象类。其中service 方法为抽象方法

2）如果新建的Servlet 程序直接继承GenericServlet 更加简洁

3）具体实现

①在GenericServlet 中声明了一个ServletConfig 类型的成员变量，在init(ServletConfig) 方法中对其初始化。

②不建议直接覆盖init(ServletConfig) ，因为如果调用super(ServletConfig)，而还有ServletConfig接口的方法，则抛出空指针异常。int(){}方法不是sevlet的声明周期方法。而init(ServletConfig)是servlet的周期方法

 1   @Override
 2     public void init(ServletConfig config) throws ServletException {
 3         this.config = config;
 4         this.init();
 5     }
 6 
 7     /**
 8      * A convenience method which can be overridden so that there's no need to
 9      * call <code>super.init(config)</code>.
10      * <p>
11      * Instead of overriding {@link #init(ServletConfig)}, simply override this
12      * method and it will be called by
13      * <code>GenericServlet.init(ServletConfig config)</code>. The
14      * <code>ServletConfig</code> object can still be retrieved via
15      * {@link #getServletConfig}.
16      * 
17      * @exception ServletException
18      *                if an exception occurs that interrupts the servlet's
19      *                normal operation
20      */
21     public void init() throws ServletException {
22         // NOOP by default
23     }

②利用了servletConfig 成员变量的方法实现了ServletConfig 接口的方法（以下是GenericServlet 的方法源码）

 1  @Override
 2     public String getInitParameter(String name) {
 3         return getServletConfig().getInitParameter(name);
 4     }
 5 
 6  @Override
 7     public Enumeration<String> getInitParameterNames() {
 8         return getServletConfig().getInitParameterNames();
 9     }
10 
11  @Override
12     public ServletConfig getServletConfig() {
13         return config;
14     }
15 
16  @Override
17     public ServletContext getServletContext() {
18         return getServletConfig().getServletContext();
19     }
20 
21 @Override
22     public String getServletName() {
23         return config.getServletName();
24     }

3.总结

　1）深刻理解servletConfig对象

　2）java的封装，继承特性