Spring+MyBatis 注入为NULL的一个case.md

这几天实习生同学遇到一个spring注入一直为null的情况。

代码:

• 监听器代码 :

  @WebListener
  public class ServletListener implements ServletContextListener{
   
      private org.apache.log4j.Logger logger = org.apache.log4j.Logger
              .getLogger(getClass());
   
      @Override
      public void contextDestroyed(ServletContextEvent sce) {
          // TODO Auto-generated method stub
      }
   
   
      @Override
      public void contextInitialized(ServletContextEvent sce) {
   
          SingleCheck check = new SingleCheck();
          check.run();
      }
   
  }

• 主入口代码:

  public class SingleCheck {
   
      private Logger logger = Logger
              .getLogger(getClass());
   
      @Resource (name = "MonitorMasterService")
      private MonitorMasterService monitorMasterService;
   
      @Resource (name = "MonitorSlaveService")
      private MonitorSlaveService monitorSlaveService;
   
      public void run() {
   
          try {
              monitorMasterService.MOnline();
              System.out.println("master 检查完成");
          } catch (Exception e) {
              e.printStackTrace();
              String strUri =
                      "http://xxx:8080/oc_alarm.php?"
                              + "mail=xx@xx.com"
                              + "&oc_msg=主库连接失败";
              try {
                  URI uri = new URI(strUri);
                  Desktop.getDesktop().browse(uri);
              } catch (Exception e1) {
                  // TODO Auto-generated catch block
                  e1.printStackTrace();
              }
   
   
          }
   
   
          try {
              monitorSlaveService.SOnline();
          } catch (Exception e) {
              e.printStackTrace();
          }
   
          try {
              monitorSlaveService.testSlaveValues();
          } catch (Exception e) {
              e.printStackTrace();
          }
   
   
      }
   
      /**     * @param args     */
       * @param args
       */
      public static void main(String[] args) {
          // TODO Auto-generated method stub
          System.out.println("test");
          ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
          System.out.println("ctx>>" + ctx);
          MonitorMasterServiceImpl mo = (MonitorMasterServiceImpl) ctx.getBean("monitorMasterServiceImpl");
          System.out.println("MonitorMasterService>>" + mo);
          mo.MOnline();
      }
  }

• MonitorMasterService

  public interface MonitorMasterService {
   
      int MOnline();
   
  }

• MonitorMasterServiceImpl

  @Service
  public class MonitorMasterServiceImpl implements MonitorMasterService{
   
      @Resource
      private MonitorMasterMapper monitorMasterMapper;
   
      @Override
      public int MOnline(){
          System.out.println("aaaaaaa");
          return monitorMasterMapper.testOnline();
      }
   
  }

• MonitorMasterMapper

  public interface MonitorMasterMapper {
   
      @Select("select 1;")
      int testOnline();
   
  }

• applicationContext.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:util="http://www.springframework.org/schema/util"       xmlns:context="http://www.springframework.org/schema/context" 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/util http://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
         xmlns:context="http://www.springframework.org/schema/context" 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/util http://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
   
   
   
      <context:property-placeholder location="classpath:config.properties" />
      <context:component-scan base-package="monitor" />
      <context:annotation-config />
   
      <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"        destroy-method="close">
          destroy-method="close">
          <property name="driverClassName" value="${driverClassName}" />
          <property name="url" value="${jdbc_url}" />
          <property name="username" value="${jdbc_username}" />
          <property name="password" value="${jdbc_password}" />
          <!--maxActive: 最大连接数量 -->
          <property name="maxActive" value="150" />
          <!--minIdle: 最小空闲连接 -->
          <property name="minIdle" value="5" />
          <!--maxIdle: 最大空闲连接 -->
          <property name="maxIdle" value="20" />
          <!--initialSize: 初始化连接 -->
          <property name="initialSize" value="30" />
          <!-- 连接被泄露时是否打印 -->
          <property name="logAbandoned" value="true" />
          <!--removeAbandoned: 是否自动回收超时连接 -->
          <property name="removeAbandoned" value="true" />
          <!--removeAbandonedTimeout: 超时时间(以秒数为单位) -->
          <property name="removeAbandonedTimeout" value="10" />
          <!--maxWait: 超时等待时间以毫秒为单位 1000等于60秒 -->
          <property name="maxWait" value="1000" />
          <!-- 在空闲连接回收器线程运行期间休眠的时间值,以毫秒为单位. -->
          <property name="timeBetweenEvictionRunsMillis" value="10000" />
          <!-- 在每次空闲连接回收器线程(如果有)运行时检查的连接数量 -->
          <property name="numTestsPerEvictionRun" value="10" />
          <!-- 1000 * 60 * 30 连接在池中保持空闲而不被空闲连接回收器线程 -->
          <property name="minEvictableIdleTimeMillis" value="10000" />
          <property name="validationQuery" value="SELECT NOW() FROM DUAL" />
      </bean>
   
      <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
          <property name="dataSource" ref="dataSource" />
          <property name="typeAliasesPackage" value="monitor.alias"/>
      </bean>
   
      <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
          <property name="basePackage"            value="monitor.master_slave.mapper,monitor.master.mapper,monitor.slave.mapper" />
              value="monitor.master_slave.mapper,monitor.master.mapper,monitor.slave.mapper" />
      </bean>
   
      <bean id="transactionManager"        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
          class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
          <property name="dataSource" ref="dataSource" />
      </bean>
      <tx:annotation-driven transaction-manager="transactionManager" />
   
  </beans>

过程中遇到的问题整理

• @Resource 和 @Autowired 的区别及优劣。
  @Autowired　＋ @Autowired = @Resource
  @Resource的注解是J2EE提供的
  一般建议使用@Resource

• Mybatis注入异常

  Exception in thread "main" org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): monitor.master.mapper.MonitorMasterMapper.testOnline
  	at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:189)
  	at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:43)
  	at org.apache.ibatis.binding.MapperProxy.cachedMapperMethod(MapperProxy.java:58)
  	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:51)
  	at com.sun.proxy.$Proxy10.testOnline(Unknown Source)
  	at monitor.master.service.impl.MonitorMasterServiceImpl.MOnline(MonitorMasterServiceImpl.java:23)
  	at monitor.master_slave.check.SingleCheck.main(SingleCheck.java:75)
  	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  	at java.lang.reflect.Method.invoke(Method.java:483)
  	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

后来发现IDEA在编译的时候没有把mapper的xml文件编译进war包里所有会有这个错误，
改成注解的形式就没有这个问题了。

• MyBatis注入异常续集

  /**
   * @param args
   */
  public static void main(String[] args) {
      // TODO Auto-generated method stub
      System.out.println("test");
      ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
      System.out.println("ctx>>" + ctx);
      MonitorMasterServiceImpl mo = (MonitorMasterServiceImpl) ctx.getBean("monitorMasterServiceImpl");
      System.out.println("MonitorMasterService>>" + mo);
      mo.MOnline();
  }

在main里面能跑通了，但是启动web 依然报了null 的错误。

按理说注入应该是没问题了。但程序放在监听器里就是有问题，由于之前没有Spring项目的经验。
猜测是不是执行到那一步没有加载applicationContext.xml
debug之后发现已经存在这个容器
补充下spring ApplicationContext配置文件的加载过程

ContextLoaderListener位于spring-web-{$version}.RELEASE.jar中，
ServletContextListener实现了ServletContextListener接口，系统启动时会回调contextInitialized()方法。
在这个方法中，利用context-param中指定的配置文件初始化ApplicationContext,然后以WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE为key，注册为servletContext的一个属性。

更具体的可以看参考链接

加载容器也没问题，那就只能是Listener的问题。

看listener的写法:

@Overridepublic void contextInitialized(ServletContextEvent sce) {
public
 
    SingleCheck check = new SingleCheck();
    check.run();
}

按我过去的经验，spring是IOC框架，实习生同学居然用了new的方式生成一个对象，感觉这里应该是有问题的，猜测应该是使用new方式生成的对象是不会加入到application context容器里的。
于是改成:

@Override
public void contextInitialized(ServletContextEvent sce) {
 
    try {
        MonitorMasterServiceImpl mo = (MonitorMasterServiceImpl) WebApplicationContextUtils.getWebApplicationContext(sce.getServletContext())
                .getBean("monitorMasterServiceImpl");
        mo.MOnline();
    } catch (Exception e) {
        e.printStackTrace();
    }
 
}

果然就完成了。
至于是不是我猜测的那样，继续查了下资料。

new的对象 是不能注入东西的，能注入其他组件的的必须是在application context中加载的单例对象。

参考资料:

• http://www.javacoder.cn/?p=337
• http://stackoverflow.com/questions/4746041/spring-injecting-a-dependency-into-a-servletcontextlistener