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>
测试展示
越努力越幸运
最后来点鸡汤吧，好久没说了，吃苦的年龄就不要选择安逸，别白了少年头，空悲切，人生赢在转折处，改变从现在开始，分享的越多，你的价值增值越大。。。。。。。。。
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