springmvc整合mybatis连接mysql是访问页面的错误信息

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springmvc整合mybatis连接mysql是访问页面的错误信息5

自己在搭一个mvc框架，在加入mybatis之后访问页面时错误信息如下：
type Exception report

message Request processing failed; nested exception is java.lang.NullPointerException

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.NullPointerException
zhha.controller.WelcomeController.Welcome(WelcomeController.java:21)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

请问这是什么问题引起的，希望得到一些解决方法的指点。附件为整个框架包。
UserService.java

package zhha.service;

import java.util.List;

import zhha.dao.UserDao;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import zhha.model.User;

@Service
public class UserService 
{
	@Autowired
	private UserDao userDao;
	
	public List<User> showUser()
	{
		userDao.select();
		List<User> userList  = userDao.select();  
        return userList;
	}
}

User.java


package zhha.model;

import java.io.Serializable; 

public class User implements Serializable { 

    /**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	
	
	private String id;
    private String name;
    private String password;
	public String getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	public String getPassword() {
		return password;
	}
	public void setId(String id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
	public void setPassword(String password) {
		this.password = password;
	}
}

UserDao.java

package zhha.dao;

import java.util.*;
import zhha.model.User;

public interface UserDao
{
	public List<User> select();
}

UserController.java

package zhha.controller;


import java.util.List;


import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import zhha.model.User;
import zhha.service.UserService;;

@Controller
@RequestMapping("/")
public class WelcomeController 
{
	private UserService userService;
	@RequestMapping({"/welcome","/"})	
	public String Welcome()
	{
		List<User> users = userService.showUser();
        System.out.println(users.size());
		return "/welcome";
	}
	
	@RequestMapping("/hello")
	public String Hello()
	{
		  System.out.println("hello--------------------");
		  return "/hello";
	}
}