springmvc与mybatis整合中的问题

今天在整合SpringMvc+Mybatis时碰到一些问题，网上找了很多资料，一直未找到问题关键点，浪费了不少时间，先将主要碰到的问题与解决方法记录下来。

问题：bean实例化失败，编译启动时问题如下：

严重: Servlet.service() for servlet [springmvc] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException

即空指针问题。之前配置文件是这样的。

<?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.xsd                          http://www.springframework.org/schema/context                          http://www.springframework.org/schema/context/spring-context.xsd                          http://www.springframework.org/schema/mvc                          http://www.springframework.org/schema/mvc/spring-mvc.xsd        http://www.springframework.org/schema/tx         http://www.springframework.org/schema/tx/spring-tx.xsd        http://www.springframework.org/schema/util        http://www.springframework.org/schema/util/spring-util.xsd">    <!-- 自动扫描 -->    <context:component-scan base-package="cn.zsf.spring.springMaven" />    <!-- 引入配置文件 -->    <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">        <property name="location" value="classpath:jdbc.properties" />    </bean>    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">        <property name="driverClassName" value="${jdbc.driverClassName}" />        <property name="url" value="${jdbc.url}" />        <property name="username" value="${jdbc.username}" />        <property name="password" value="${jdbc.password}" />        <!-- 初始化连接大小 -->        <property name="initialSize" value="${jdbc.initialSize}" />        <!-- 连接池最大数量 -->        <property name="maxActive" value="${jdbc.maxActive}" />        <!-- 连接池最大空闲 -->        <property name="maxIdle" value="${jdbc.maxIdle}" />        <!-- 连接池最小空闲 -->        <property name="minIdle" value="${jdbc.minIdle}" />        <!-- 获取连接最大等待时间 -->        <property name="maxWait" value="${jdbc.maxWait}" />    </bean>    <!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 -->    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">        <property name="dataSource" ref="dataSource" />        <property name="configLocation"  value="classpath:sqlMapConfig.xml"/>        <!-- 自动扫描mapping.xml文件，**表示迭代查找,也可在sqlMapConfig.xml中单独指定xml文件-->        <property name="mapperLocations" value="classpath:cn/zsf/spring/springMaven/mapping/*.xml" />    </bean>    <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">      <constructor-arg index="0" ref="sqlSessionFactory"/>  </bean>     <!-- (事务管理)transaction manager, use JtaTransactionManager for global tx -->    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">        <property name="dataSource" ref="dataSource" />    </bean></beans>

我在UserService中注入

package cn.zsf.spring.springMaven.service;

import org.apache.log4j.Logger;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import cn.zsf.spring.springMaven.dao.UserMapper;
import cn.zsf.spring.springMaven.pojo.User;

@Service
public class UserService {
    private static Logger logger = Logger.getLogger(UserService.class);
    
    @Autowired
    private SqlSessionTemplate sqlSession;
    
    @Autowired
    private UserMapper userMapper;
  
    
    public User get(int id){
        logger.info(sqlSession.toString());
        return  userMapper.selectByPrimaryKey(id);
    }
    
    public void setUserMapper(UserMapper userMapper){
        this.userMapper = userMapper;
    }
    
    public UserMapper getUserMapper(){
        return userMapper;
    }
    
    
}

在启动时就报错，sqlSession注入失败，userMapper也找不到可用的bean，错误信息为：

ERROR [web.context.ContextLoader] Context initialization failed
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'homeController': Unsatisfied dependency expressed through field 'userService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService': Unsatisfied dependency expressed through field 'userMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'cn.zsf.spring.springMaven.dao.UserMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)

造成sqlSession、userMapper都无法注入成功，原因是配置错误，未配置mybatis mapper接口，在spring-mybatis.xml中

<bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">      <constructor-arg index="0" ref="sqlSessionFactory"/>  </bean> 

后面添加

<!-- 配置mybatis mapper接口 -->    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">        <property name="basePackage" value="cn.zsf.spring.springMaven.**.dao"/>        <property name="sqlSessionTemplateBeanName" value="sqlSessionTemplate"/>    </bean>

即可；

另外碰到一个问题，错误提示信息

严重: Servlet.service() for servlet [springmvc] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at cn.zsf.spring.springMaven.service.UserService.get(UserService.java:46)

在HomeController中调用 userService.get(1)方法， 错误原因为：在我直接手动进行service初始化， UserService userService = new UserService();  这是一个低级错误，因UserService中有注入sqlsession和userMapper，并注册为Service，通过手动new的方式，是无法完成这两个属性的注入的，因此调用自然也就错误了。 其必须通过

@Autowired

private UserMapper userMapper

的方式进行注入引用。

这里附上其他的配置文件(可正常使用)：

sqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE configuration PUBLIC      "-//mybatis.org//DTD Config 3.0//EN"      "http://mybatis.org/dtd/mybatis-3-config.dtd">  <configuration>      <typeAliases>        <typeAlias type="cn.zsf.spring.springMaven.pojo.User" alias="UserEntry" />    </typeAliases></configuration>

applicationContent.xml

<?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:context="http://www.springframework.org/schema/context"    xmlns:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop"    xmlns:tx="http://www.springframework.org/schema/tx"    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd     http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd     http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">      <!-- 此行语句使得resource autowired 等四个注解可以使用 -->   <context:component-scan base-package="cn.zsf.spring.springMaven" />       <!-- 配置读取外部配置文件 -->    <context:property-placeholder location="classpath:jdbc.properties" />        <context:annotation-config />        <!-- 事务扫描开始(开启@Tranctional) -->    <tx:annotation-driven transaction-manager="transactionManager" />        </beans>

spring-mvc.xml

<?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.xsd    http://www.springframework.org/schema/context    http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"default-lazy-init="true"><!-- 启动事务添加配置 -->    <context:component-scan base-package="cn.zsf.spring.springMaven">          <!-- 排除扫描service标签 -->        <!-- <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Service"/> -->     </context:component-scan>        <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">    <property name="messageConverters">    <list>    <ref bean="mappingJacksonHttpMessageConverter"/>    <ref bean="utf8StringHttpMessageConverter" />    </list>    </property>    </bean>        <bean id="mappingJacksonHttpMessageConverter" class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">          <property name="supportedMediaTypes">              <list>                  <value>text/plain;charset=UTF-8</value>                <value>text/html;charset=UTF-8</value>                  <value>application/json;charset=UTF-8</value>            </list>          </property>      </bean>      <bean id="utf8StringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter">        <property name="supportedMediaTypes">            <list>                <value>text/plain;charset=UTF-8</value>                <value>text/html;charset=UTF-8</value>                <value>application/json;charset=UTF-8</value>            </list>        </property>    </bean>         <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">    <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>        <property name="prefix" value="/WEB-INF/views/"/>        <property name="suffix" value=".jsp"/>    </bean>        <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"></bean>        <!-- 当配置了<mvc:annotation-driven/>后，会自动加载org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping和org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter，所以如果显示的配置则需去掉配置<mvc:annotation-driven/> -->    <!--<mvc:annotation-driven/>-->    </beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">  <display-name>Zsf Web Application</display-name>   <!-- 配置web.xml，使其具有springmvc特性，主要配置两处，一个是ContextLoaderListener，一个是DispatcherServlet -->    <context-param>        <param-name>contextConfigLocation</param-name>        <param-value>classpath*:applicationContext.xml,        classpath*:spring-mybatis.xml,        </param-value>    </context-param>        <!-- 配置ContextLoaderListener表示，该工程要以spring的方式启动。启动时会默认在/WEB-INF目录下查找applicationContext.xml作为spring容器的配置文件，该文件里可以初始化一些bean -->    <listener>        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>    </listener>        <!-- 字符集过滤器 -->      <filter>        <filter-name>encodingFilter</filter-name>        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>        <init-param>            <param-name>encoding</param-name>            <param-value>UTF-8</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>encodingFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>        <!-- spring mvc 配置 -->    <!-- 配置DispatcherServlet表示，该工程将采用springmvc的方式。启动时也会默认在/WEB-INF目录下查找XXX-servlet.xml作为配置文件，        XXX就是DispatcherServlet的名字，该文件中将配置两项重要的mvc特性：HandlerMapping,负责为DispatcherServlet这个前端控制器的请求查找Controller；        ViewResolver,负责为DispatcherServlet查找ModelAndView的视图解析器。        此处使用指定的配置文件spring-mvc.xml -->    <servlet>        <servlet-name>springmvc</servlet-name>        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>        <init-param>              <param-name>contextConfigLocation</param-name>              <!--<param-value>/WEB-INF/classes/spring-mvc-servlet.xml</param-value>-->            <param-value>/WEB-INF/classes/spring-mvc.xml</param-value>        </init-param>          <load-on-startup>1</load-on-startup>      </servlet>    <servlet-mapping>        <servlet-name>springmvc</servlet-name>        <url-pattern>/</url-pattern>    </servlet-mapping>        <welcome-file-list>          <welcome-file>index.jsp</welcome-file>      </welcome-file-list>        </web-app>