1 import javax.servlet.*; 2 import javax.servlet.ServletConfig; 3 import javax.servlet.ServletException; 4 import javax.servlet.ServletRequest; 5 import javax.servlet.ServletResponse; 6 import java.io.IOException; 7  8 //使用servlet接口方式开发 9 import javax.servlet.*;10 import java.io.*;11 12 public class Hello  implements Servlet {13         14     //该函数用于初始化该servlet（类似于类的构造函数）15     //该函数只会被调用一次（当用户第一次访问该servlet时被调用）16     public void init(ServletConfig parm1) throws ServletException {17     }18 19     public ServletConfig getServletConfig() {20         return null;21     }22 23     //该函数用于处理业务逻辑24     //应当把业务逻辑代码写在这个函数中25     //用户每次访问该servlet时。都会调用26     //req用于获得客户端信息，res用于向客户端返回信息27     public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {28         System.out.println("service it");29         PrintWriter pw=res.getWriter();30         pw.println("hello,world");31     }32 33     public String getServletInfo() {34         return "";35     }36 37     public void destroy() {38         //销毁servlet实例39         //reload、关闭tomcat时会调用40     }41 }

 1 import javax.servlet.GenericServlet; 2 import javax.servlet.*; 3 import java.io.*; 4  5 public class HelloGen extends GenericServlet{ 6     public void service(ServletRequest req,ServletResponse res){ 7      8     try{ 9         PrintWriter pw=res.getWriter();10         pw.println("Hello,world! generic");11     }12     catch(Exception e){13         e.printStackTrace();14     }15     }16 }

 1 public class HelloHttp extends HttpServlet{ 2      3     public void doGet(HttpServletRequest req,HttpServletResponse res){ 4         try{ 5             PrintWriter pw=res.getWriter(); 6             pw.println("Hello,http"); 7         } 8         catch(Exception e){ 9             e.printStackTrace();10         }11     }12     13     public void doPost(HttpServletRequest req,HttpServletResponse res){14         this.doGet(req,res);15     }16 }