package com.itheima.b_login;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import sun.security.util.Password;/**?* Servlet implementation class UserServlet?*/public class UserServlet extends HttpServlet {?? ?private static final long serialVersionUID = 1L;?? ?protected void doGet(HttpServletRequest request, HttpServletResponse response)?? ??? ??? ?throws ServletException, IOException {?? ??? ?try {?? ??? ??? ?String username = request.getParameter("username");?? ??? ??? ?String password = request.getParameter("password");?? ??? ??? ?User user = new User();?? ??? ??? ?user.setUsername(username);?? ??? ??? ?user.setUsername(password);?? ??? ??? ?UserService userService = new UserService();?? ??? ??? ?User existUser = userService.login(user);?? ??? ?} catch (Exception e) {?? ??? ??? ?e.printStackTrace();?? ??? ?}?? ?}?? ?protected void doPost(HttpServletRequest request, HttpServletResponse response)?? ??? ??? ?throws ServletException, IOException {?? ??? ?doGet(request, response);?? ?}}請問代碼中的異常已經拋出了 為神惡魔還要try catch;它倆有什么不同,以及什么時候用, 什么時候一起用?