Servlet中實現多個功能案例

如何實現一個Servlet中的多個功能

前言：唉，打臉了，前腳剛說過要跟Servlet正式告別，后腳這不又來了，哈哈，總結出一點東西，糾結了一下還是做個分享吧，學習知識比面子重要，對吧，下回再也不約Servlet了。

需求分析

看下面代碼，現在有一個UserServlet，里面有增刪改查四個方法，按平常的思維，用一個Servlet實現一個功能，這沒毛病，現在問題是一個Servlet中有四個功能，那這該如何去實現呢？

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","刪除成功");
        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","查詢成功");
        return "add.jsp";
    }

}

 

解決思維

解決這個問題其實也簡單，再寫一個FatherServlet繼承於HttpServlet,在這個父類Servlet中的service()方法中通過請求參數判斷要調用的子類UserServlet中的哪個方法並執行，可能說到這有些朋友不懂了，如何用參數去判斷大家一看下面的代碼就明白了，我主要解釋一下大家的疑惑，子類UserServlet如何去調用父類FatherServlet中的service()方法，其實秘訣就在這個參數上，在訪問UserSerlvet時帶上請求參數，訪問過來后UserServlet中沒有解決參數的方法，所以他會在父類FatherServlet中尋找響應的方法，找到后執行，這是繼承的，子類繼承父類的方法沒毛病吧，所以就解決了。

 

解決完這個問題后我還在service()方法中加了判斷是重定向還是轉發的思維，這個就友情贈送了，不說了，來，看代碼：

 

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("參數不能為空");

        }



        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);



            //判斷返回值的前綴，默認轉發，r:重定向  f:轉發

            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("請求的方法不存在！！");

        } catch (IllegalAccessException e) {

            throw new RuntimeException("請求方法執行異常！！");

        } catch (InvocationTargetException e) {

            throw new RuntimeException("請求方法執行異常！！");

        }

    }

}
 

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","刪除成功");

        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","查詢成功");

        return "add.jsp";

    }



}

完整演示

此篇主要是解決題目所示的需求，先在需求解決了，做戲還要做全呢，我就把我測試的代碼都整理出來，方便新手去學習。

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中的添加功能實現了");

    }



    @Override

    public void delete() {

        System.out.println("UserDao中的刪除功能實現了");

    }



    @Override

    public void update() {

        System.out.println("UserDao中的修改功能實現了");

    }



    @Override

    public void query() {

        System.out.println("UserDao中的查詢功能實現了");

    }

}
 

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","刪除成功");

        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","查詢成功");

        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("參數不能為空");

        }



        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);



            //判斷返回值的前綴，默認轉發，r:重定向  f:轉發

            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("請求的方法不存在！！");

        } catch (IllegalAccessException e) {

            throw new RuntimeException("請求方法執行異常！！");

        } catch (InvocationTargetException e) {

            throw new RuntimeException("請求方法執行異常！！");

        }

    }

}

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>測試頁面</title>

</head>

<body>



<h1>測試</h1>

${mess}



</body>

</html>

測試展示

 

越努力越幸運

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