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，後腳這不又來了，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
看下面程式碼，現在有一個UserServlet，裡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","新增成功");
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()方法中通過請求引數判斷要呼叫的子類UserServlet中的哪個方法並執行，可能說到這有些朋友不懂了，如何用引數去判斷大家一看下面的程式碼就明白了，我主要解釋一下大家的疑惑，子類UserServlet如何去呼叫父類FatherServlet中的service()方法，其實祕訣就在這個引數上，在訪問UserSerlvet時帶上請求引數，訪問過來後UserServlet中沒有解決引數的方法，所以他會在父類FatherServlet中尋找響應的方法，找到後執行，這是繼承的，子類繼承父類的方法沒毛病吧，所以就解決了。
解決完這個問題後我還在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，看程式碼：
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("引數不能為空");
}
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);
//判斷返回值的字首，預設轉發，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","新增成功");
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，我就把我測試的程式碼都整理出來，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中的新增功能實現了");
}
@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","新增成功");
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("引數不能為空");
}
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);
//判斷返回值的字首，預設轉發，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
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