第一步改进，GenericServlet：
我们目前所有放入Servlet类直接实现了javax.servlet.Servlet接口，但是这个接口中有很多方法是目前不需要的，我们可能只需要编写service。直接实现Servlet接口代码丑陋，有必要在中间添加一个适配器，以后所有的Servlet类不再直接实现Servlet接口，应该去继承适配器类。
适配器除了可以让代码优雅之外，我们还可以在适配器中提供大量的方法，子类继承之后，可以在子类中直接使用，方便编程。
自己使用缺省适配器设计模式实现的GenericServlet类：
1 package com.bjpowernode.javaweb.servlet;
2
3 import java.io.IOException;
4
5 import javax.servlet.Servlet;
6 import javax.servlet.ServletConfig;
7 import javax.servlet.ServletContext;
8 import javax.servlet.ServletException;
9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11
12 /*
13 * GenericSerrvlet是一个适配器，这个适配器是一个Servlet
14 * 以后javaweb程序员无需直接实现Servlet接口，去继承这个适配器即可，重写service方法。
15 *
16 * @author Administrator
17 */
18
19 public abstract class GenericServlet implements Servlet {
20
21 ServletConfig config;
22
23 //该方法不能被覆盖，因为被覆盖之后，config就获取不到了，所以方法前面加了final
24 public final void init(ServletConfig config) throws ServletException {
25 this.config = config;
26 this.init();
27 }
28
29 /*
30 * 若在初始化时刻需要执行一段特殊的代码，建议重写无参数的init方法，注意动态绑定，会让上面的init方法调用子类重写的init方法
31 */
32 public void init(){
33
34 }
35
36 public abstract void service(ServletRequest request, ServletResponse response)
37 throws ServletException, IOException;
38
39 public void destroy() {
40
41 }
42
43 public ServletConfig getServletConfig() {
44 return config;
45 }
46
47 public String getServletInfo() {
48 return "qjj";
49 }
50
51 //---------------------以下所有的方法都是拓展方法，方便子类的使用------------------------------
52
53 public ServletContext getServletContext(){
54 return getServletConfig().getServletContext();
55 }
56 }
其实sun公司已经为我们实现了这个适配器类，可以直接调用：
1 package com.bjpowernode.javaweb.servlet;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.ServletException;
7 import javax.servlet.ServletRequest;
8 import javax.servlet.ServletResponse;
9
10 //public class HelloServlet extends GenericServlet {
11 public class HelloServlet extends javax.servlet.GenericServlet {
12 //sun公司已经为我们写了适配器，并且里面有很多其他的方法
13
14 private static final long serialVersionUID = 1L;
15
16 @Override
17 public void init() {
18 System.out.println("HelloServlet‘s init......");
19 }
20
21 @Override
22 public void service(ServletRequest request, ServletResponse response)
23 throws ServletException, IOException {
24 response.setContentType("text/html;charset=UTF-8");
25 PrintWriter out = response.getWriter();
26 out.print("hello world!");
27 out.print("<br>");
28 out.print(getServletContext());
29 }
30
31 }
HTTP协议相关：
前端页面中的GET请求和POST请求代码：
1 <html> 2 <head> 3 <title>login page</title> 4 <meta name="keywords" content="keyword1,keyword2,keyword3"> 5 <meta name="description" content="this is my page"> 6 <meta name="content-type" content="text/html; charset=UTF-8"> 7 </head> 8 <body> 9 10 GET方式 11 <form action="/prj-servlet-09/system/login"> 12 username<input type="text" name="username"><br> 13 password<input type="password" name="password"><br> 14 <input type="submit" value="login"> 15 </form> 16 <hr> 17 GET方式 18 <form action="/prj-servlet-09/system/login" method="get"> 19 username<input type="text" name="username"><br> 20 password<input type="password" name="password"><br> 21 <input type="submit" value="login"> 22 </form> 23 <hr> 24 POST方式 25 <form action="/prj-servlet-09/system/login" method="post"> 26 username<input type="text" name="username"><br> 27 password<input type="password" name="password"><br> 28 <input type="submit" value="login"> 29 </form> 30 </body> 31 32 </html>
第二步改进，HTTPServlet：
具体代码实现：
1 package com.bjpowernode.javaweb.servlet;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.GenericServlet;
7 import javax.servlet.ServletException;
8 import javax.servlet.ServletRequest;
9 import javax.servlet.ServletResponse;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12
13 public class LoginServlet extends GenericServlet {
14
15 private static final long serialVersionUID = 1L;
16
17 @Override
18 public void service(ServletRequest req, ServletResponse res)
19 throws ServletException, IOException {
20 //将ServletRequest,ServletResponse强制类型转换成带有Http的接口类型
21 HttpServletRequest request = (HttpServletRequest)req;
22 HttpServletResponse response = (HttpServletResponse)res;
23
24 response.setContentType("text/html;charset=UTF-8");
25 PrintWriter out = response.getWriter();
26
27 //获取浏览器发送的请求方式
28 String method = request.getMethod();
29 //LoginServlet是处理登录的，要求前端必须发送POST请求
30 if("GET".equals(method)){
31 //前端报错
32 out.print("405-您应当发送POST请求");
33 //后端报错
34 throw new RuntimeException("405-您应当发送POST请求");
35 }
36
37 //若程序执行到这里证明用户发送到的请求是POST请求，程序应当正常执行
38 out.print("正在登录...");
39 }
40
41 }
解决方法：自己用模板方法设计模式设计HTTPServlet：
1 package com.bjpowernode.javaweb.servlet;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.GenericServlet;
7 import javax.servlet.ServletException;
8 import javax.servlet.ServletRequest;
9 import javax.servlet.ServletResponse;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12
13 public class HttpServlet extends GenericServlet {
14
15 private static final long serialVersionUID = 1L;
16
17 @Override
18 public void service(ServletRequest req, ServletResponse res)
19 throws ServletException, IOException {
20 HttpServletRequest request = (HttpServletRequest)req;
21 HttpServletResponse response = (HttpServletResponse)res;
22 service(request,response);
23 }
24
25 public void service(HttpServletRequest request, HttpServletResponse response)
26 throws ServletException, IOException {
27 String method = request.getMethod();
28 if("GET".equals(method)){
29 doGet(request,response);
30 }else if("POST".equals(method)){
31 doPost(request,response);
32 }
33 }
34
35 public void doGet(HttpServletRequest request, HttpServletResponse response)
36 throws ServletException, IOException {
37 response.setContentType("text/html;charset=UTF-8");
38 PrintWriter out = response.getWriter();
39 out.print("405-您应当发送POST请求");
40 throw new RuntimeException("405-您应当发送POST请求");
41 }
42
43 public void doPost(HttpServletRequest request, HttpServletResponse response)
44 throws ServletException, IOException {
45 response.setContentType("text/html;charset=UTF-8");
46 PrintWriter out = response.getWriter();
47 out.print("405-您应当发送GET请求");
48 throw new RuntimeException("405-您应当发送GET请求");
49 }
50
51 }
接下写自己的Servlet时，要继承自HttpServlet，为get请求则重写doGet方法，为post请求则重写doPost方法。
其实sun公司已经为我们实现了这个HttpServlet类，可以直接调用：
1 package com.bjpowernode.javaweb.servlet;
2
3 import java.io.IOException;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.http.HttpServletRequest;
7 import javax.servlet.http.HttpServletResponse;
8
9 //public class LoginServlet extends HttpServlet {
10 public class LoginServlet extends javax.servlet.http.HttpServlet {
11
12 private static final long serialVersionUID = 1L;
13
14 @Override
15 public void doPost(HttpServletRequest request, HttpServletResponse response)
16 throws ServletException, IOException {
17 response.getWriter().print("login......");
18 }
19 }
至此，以后写自己的Servlet时，都要继承自HttpServlet，并且使用doPost或者doGet方法。
时间： 2024-11-01 23:12:08