如何实现一个Servlet中的多个功能

现在有一个UserServlet，里面有增删改查四个方法，按平常的思维，用一个Servlet实现一个功能，这没毛病，现在问题是一个Servlet中有四个功能，那这该如何去实现呢？

package com.my.servlet;
import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends HttpServlet {
   private UserService userService = new UserServiceImpl();
 public String add(HttpServletRequest request,HttpServletResponse response){
     userService.add();
     request.setAttribute("mess","添加成功");
     return "r:add.jsp";
 }
   public String delete(HttpServletRequest request,HttpServletResponse response){
       userService.delete();
       request.setAttribute("mess","删除成功");
       return "f:add.jsp";
   }
   public String update(HttpServletRequest request,HttpServletResponse response){
       userService.update();
       request.setAttribute("mess","修改成功");
       return "add.jsp";
   }
   public String query(HttpServletRequest request,HttpServletResponse response){
       userService.query();
       request.setAttribute("mess","查询成功");
       return "add.jsp";
   }
}

解决思维

解决这个问题其实也简单，再写一个FatherServlet继承于HttpServlet,在这个父类Servlet中的service()方法中通过请求参数判断要调用的子类UserServlet中的哪个方法并执行，可能说到这有些朋友不懂了，如何用参数去判断大家一看下面的代码就明白了，我主要解释一下大家的疑惑，子类UserServlet如何去调用父类FatherServlet中的service()方法，其实秘诀就在这个参数上，在访问UserSerlvet时带上请求参数，访问过来后UserServlet中没有解决参数的方法，所以他会在父类FatherServlet中寻找响应的方法，找到后执行，这是继承的，子类继承父类的方法没毛病吧，所以就解决了。

解决完这个问题后我还在service()方法中加了判断是重定向还是转发的思维，这个就友情赠送了，不说了，来，看代码：

FatherServlet：

package com.my.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class FatherServlet extends HttpServlet {
   @Override
   protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       String m = req.getParameter("m");
       if (m==null||"".equals(m)){
           throw new RuntimeException("参数不能为空");
       }

       Class c = this.getClass();
       try {
           Method method = c.getMethod(m,HttpServletRequest.class,HttpServletResponse.class);
           Object o =method.invoke(this,req,resp);
           String rel =String.valueOf(o);

           //判断返回值的前缀，默认转发，r:重定向  f:转发
           if (rel.startsWith("r:")){
              rel =  rel.substring(rel.indexOf(":")+1);
              resp.sendRedirect(rel);
           }else if(rel.startsWith("f:")){
               rel = rel.substring(rel.indexOf(":")+1);
               req.getRequestDispatcher(rel).forward(req,resp);
           }else {
               req.getRequestDispatcher(rel).forward(req,resp);
           }
       } catch (NoSuchMethodException e) {
           throw new RuntimeException("请求的方法不存在！！");
       } catch (IllegalAccessException e) {
           throw new RuntimeException("请求方法执行异常！！");
       } catch (InvocationTargetException e) {
           throw new RuntimeException("请求方法执行异常！！");
       }
   }
}

UserServlet：

package com.my.servlet;

import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends FatherServlet {
   private UserService userService = new UserServiceImpl();
 public String add(HttpServletRequest request,HttpServletResponse response){
     userService.add();
     request.setAttribute("mess","添加成功");
     return "r:add.jsp";
 }
   public String delete(HttpServletRequest request,HttpServletResponse response){
       userService.delete();
       request.setAttribute("mess","删除成功");
       return "f:add.jsp";
   }
   public String update(HttpServletRequest request,HttpServletResponse response){
       userService.update();
       request.setAttribute("mess","修改成功");
       return "add.jsp";
   }
   public String query(HttpServletRequest request,HttpServletResponse response){
       userService.query();
       request.setAttribute("mess","查询成功");
       return "add.jsp";
   }
}

完整演示

此篇主要是解决题目所示的需求，先在需求解决了，做戏还要做全呢，我就把我测试的代码都整理出来，方便新手去学习。

UserDao

package com.my.dao;

public interface UserDao {
   public void add();
   public void delete();
   public void update();
   public void query();
}

UserDaoImpl

package com.my.dao.impl;
import com.my.dao.UserDao;
public class UserDaoImpl implements UserDao {
   @Override
   public void add() {
       System.out.println("UserDao中的添加功能实现了");
   }
   @Override
   public void delete() {
       System.out.println("UserDao中的删除功能实现了");
   }
   @Override
   public void update() {
       System.out.println("UserDao中的修改功能实现了");
   }
   @Override
   public void query() {
       System.out.println("UserDao中的查询功能实现了");
   }
}

UserService

package com.my.service;

public interface UserService {
   public void add();
   public void delete();
   public void update();
   public void query();
}

UserServiceImpl

package com.my.service.impl;
import com.my.dao.UserDao;
import com.my.dao.impl.UserDaoImpl;
import com.my.service.UserService;
public class UserServiceImpl implements UserService {
   private UserDao userDao = new UserDaoImpl();
   @Override
   public void add() {
       userDao.add();
   }
   @Override
   public void delete() {
       userDao.delete();
   }

   @Override
   public void update() {
       userDao.update();
   }

   @Override
   public void query() {
       userDao.query();
   }
}

UserServlet

package com.my.servlet;

import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends FatherServlet {
   private UserService userService = new UserServiceImpl();
 public String add(HttpServletRequest request,HttpServletResponse response){
     userService.add();
     request.setAttribute("mess","添加成功");
     return "r:add.jsp";
 }
   public String delete(HttpServletRequest request,HttpServletResponse response){
       userService.delete();
       request.setAttribute("mess","删除成功");
       return "f:add.jsp";
   }
   public String update(HttpServletRequest request,HttpServletResponse response){
       userService.update();
       request.setAttribute("mess","修改成功");
       return "add.jsp";
   }
   public String query(HttpServletRequest request,HttpServletResponse response){
       userService.query();
       request.setAttribute("mess","查询成功");
       return "add.jsp";
   }
}

FatherServlet

package com.my.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class FatherServlet extends HttpServlet {

   @Override
   protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       String m = req.getParameter("m");
       if (m==null||"".equals(m)){
           throw new RuntimeException("参数不能为空");
       }

       Class c = this.getClass();

       try {
           Method method = c.getMethod(m,HttpServletRequest.class,HttpServletResponse.class);
           Object o =method.invoke(this,req,resp);
           String rel =String.valueOf(o);

           //判断返回值的前缀，默认转发，r:重定向  f:转发
           if (rel.startsWith("r:")){
              rel =  rel.substring(rel.indexOf(":")+1);
              resp.sendRedirect(rel);
           }else if(rel.startsWith("f:")){
               rel = rel.substring(rel.indexOf(":")+1);
               req.getRequestDispatcher(rel).forward(req,resp);
           }else {
               req.getRequestDispatcher(rel).forward(req,resp);
           }
       } catch (NoSuchMethodException e) {
           throw new RuntimeException("请求的方法不存在！！");
       } catch (IllegalAccessException e) {
           throw new RuntimeException("请求方法执行异常！！");
       } catch (InvocationTargetException e) {
           throw new RuntimeException("请求方法执行异常！！");
       }
   }
}

add.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="z" uri="http://mycompany.com" %>
<html>
<head>
   <title>测试页面</title>
</head>
<body>
<h1>测试</h1>
${mess}
</body>
</html>

测试展示

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