我正在尝试使用mybatis运行一个简单的sql查询，但是它给了我以下异常

java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.mycom.myproject.db.mybatis.dao.UserMapper.countByExample
org.apache.ibatis.session.Configuration$StrictMap.get(Configuration.java:660)
org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:495)
org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:488)
org.apache.ibatis.binding.MapperMethod.setupCommandType(MapperMethod.java:236)
org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:71)
org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:39)
$Proxy9.countByExample(Unknown Source)
com.mycom.myproject.controller.LoginController.login(LoginController.java:39)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:601)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:213)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

我的UserMapper.xml是

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.mycom.myproject.db.mybatis.dao.UserMapper" >
<select id="countByExample" resultType="int">
select count(*) from users
</select>
</mapper>

我的UserMapper是

public interface UserMapper {
   int countByExample();
}

我试图在我的LoginController中访问它

public class LoginController
 {
static final Logger logger = Logger.getLogger(LoginController.class);

@Autowired
private UserMapper userMapper;



@RequestMapping("/login")
public ModelAndView login(@ModelAttribute User userBean, Model model){

    int count = userMapper.countByExample();

    System.out.println("Count: "+ count);

    return new ModelAndView("login", "userBean", userBean);

}
    }

我的spring-servlet.xml文件是

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.1.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd">



<context:annotation-config />

<context:component-scan
    base-package="com.mycom.myproject" />

<!-- Enable annotation driven controllers, validation etc... -->
<mvc:annotation-driven />

<mvc:resources mapping="/resources/**" location="/resources/" />


<bean id="datasource" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://localhost/mydatabase"/>
    <property name="username" value="root"/>
    <property name="password" value="root"/>
</bean>

<!-- Declare a transaction manager -->

<bean id="transactionManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager"
p:dataSource-ref="datasource" />


<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="datasource" />
</bean>

<!-- scan for mappers and will automatically scan the whole classpath for xmls -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="sqlSessionFactory" ref="sqlSessionFactory" />
    <property name="basePackage" value="com.mycom.myproject.db.mybatis.dao" />
</bean>


<bean id="viewResolver"
    class="org.springframework.web.servlet.view.UrlBasedViewResolver">
    <property name="viewClass"
        value="org.springframework.web.servlet.view.JstlView" />
    <property name="prefix" value="/WEB-INF/jsp/" />
    <property name="suffix" value=".jsp" />
</bean>

我不知道为什么会出现此错误。