Servlet笔记6--Servlet程序改进
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。
