Servlet中实现多个功能案例

如何实现一个Servlet中的多个功能

前言：唉，打脸了，前脚刚说过要跟Servlet正式告别，后脚这不又来了，哈哈，总结出一点东西，纠结了一下还是做个分享吧，学习知识比面子重要，对吧，下回再也不约Servlet了。

需求分析

看下面代码，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>