求助！JSP跳转servlet 404报错

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这是项目结构:

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UserDAO.java :

package dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import beans.User;

public class UserDAO {
	public static final String DRIVER = "com.mysql.jdbc.Driver";
	public static final String DBURL = "jdbc:mysql://localhost:3306/user_info";
	public static final String DBUSER = "root";
	public static final String DBPASS = "1234";

	private Connection conn = null;
	private PreparedStatement pStat = null;
	private ResultSet rs = null;

	// 获得数据库连接
	public Connection getConnection() {
		try {
			Class.forName(DRIVER).newInstance();
			return DriverManager.getConnection(DBURL, DBUSER, DBPASS);
		} catch (Exception e) {
			return null;
		}
	}

	// 关闭数据库连接
	public void close() {
		try {
			if (rs != null) {
				rs.close();
			}
			if (pStat != null) {
				pStat.close();
			}
			if (conn != null) {
				conn.close();
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	// 根据用户名查找
	public boolean findUserByUsername(String username) {
		conn = getConnection();
		try {
			pStat = conn.prepareStatement("select * from users where username=?");
			pStat.setString(1, username);
			rs = pStat.executeQuery();
			if (rs.next()) {
				return true;
			} else {
				return false;
			}
		} catch (SQLException e) {
			return false;
		} finally {
			close();
		}
	}

	// 根据用户名，密码查找
	public boolean findUser(String username, String password) {
		conn = getConnection();
		try {
			pStat = conn.prepareStatement("select * from users where username=? password=?");
			pStat.setString(1, username);
			pStat.setString(2, password);
			rs = pStat.executeQuery();
			if (rs.next()) {
				return true;
			} else {
				return false;
			}
		} catch (Exception e) {
			return false;
		}finally {
			close();
		}
	}
	
	//添加用户
	public boolean add(User user) {
		conn=getConnection();
		try {
			pStat=conn.prepareStatement("insert into users values(null,?,?)");
			pStat.setString(1, user.getUsername());
			pStat.setString(2, user.getPassword());
			int cnt=pStat.executeUpdate();		//executeUpdate 的返回值是一个整数，指示受影响的行数（即更新计数）
			if(cnt>0) {
				return true;
			}else {
				return false;
			}
		}catch(Exception e){
			return false;
		}finally {
			close();
		}
	}
}

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RegServlet.java :

package servlets;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import beans.User;
import dao.UserDAO;

public class RegServlet extends HttpServlet {

	@Override
	public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		String path = request.getContextPath();
		User user = new User();
		user.setUsername(username);
		user.setPassword(password);
		UserDAO userdao = new UserDAO();
		if (userdao.findUserByUsername(username)) {
			request.getSession().setAttribute("err", "用户名已存在");
			response.sendRedirect(path + "/register.jsp");
		} else {
			boolean flag = userdao.add(user);
			if (flag) {
				request.getSession().setAttribute("username", username);
				response.sendRedirect(path + "/welcome.jsp");
			} else {
				request.getSession().setAttribute("err", "注册失败");
				response.sendRedirect(path + "/register.jsp");
			}
		}
	}

}

LoginServlet:

package servlets;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import dao.UserDAO;

public class LoginServlet extends HttpServlet {

	@Override
	public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		String path = request.getContextPath();
		UserDAO userdao = new UserDAO();
		boolean flag = userdao.findUser(username, password);
		if (flag) {
			request.getSession().setAttribute("username", username);
			response.sendRedirect(path + "/welcome.jsp");
		} else {
			request.getSession().setAttribute("err", "登陆失败");
			response.sendRedirect(path + "/login.jsp");
		}

	}

}

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login.jsp:

	<form action="/LoginServlet">
     	   用户名<input type="text" name="username"><br>
    	   密码<input type="password" name="password"><br>
        <input type="submit" value="登录">
        <input type="reset" value="重填">
 	</form> 

register.jsp:

<form action="/RegServlet">
		用户名<input type="text" name="username"><br>
		密码<input type="password" name="password"><br> 
		<input type="submit" value="注册"> 
		<input type="reset" value="重填">
	</form>

web.xml :

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="WebApp_ID" version="3.0">	
	
	<display-name>MVC_Test</display-name>
	<welcome-file-list>
		<welcome-file>register.jsp</welcome-file>
	</welcome-file-list>

	<servlet>
		<servlet-name>RegServlet</servlet-name>
		<servlet-class>servlets.RegServlet</servlet-class>
	</servlet>
	<servlet>
		<servlet-name>LoginServlet</servlet-name>
		<servlet-class>servlets.LoginServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>RegServlet</servlet-name>
		<url-pattern>/RegServlet</url-pattern>
	</servlet-mapping>
	<servlet-mapping>
		<servlet-name>LoginServlet</servlet-name>
		<url-pattern>/LoginServlet</url-pattern>
	</servlet-mapping>
</web-app>