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 {@Overrideprotected 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 {@Overridepublic void add() {System.out.println("UserDao中的添加功能实现了");}@Overridepublic void delete() {System.out.println("UserDao中的删除功能实现了");}@Overridepublic void update() {System.out.println("UserDao中的修改功能实现了");}@Overridepublic 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();@Overridepublic void add() {userDao.add();}@Overridepublic void delete() {userDao.delete();}@Overridepublic void update() {userDao.update();}@Overridepublic 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 {@Overrideprotected 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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转载于:https://www.cnblogs.com/zyx110/p/11286828.html