Log表示autowire已完成，但在使用该对象时会抛出NPE

Question

我正在尝试使用@Autowire注入DAO。将日志级别设置为debug，我可以看到bean已创建并连接到服务类，但是，当我尝试使用注入的对象时，会抛出nullpointerexecption。

英语不是我的主要语言，但是查看下面的日志，似乎DAO已创建并正确连接到服务：

DefaultListableBeanFactory:221 - Creating shared instance of singleton bean 'ticketServiceImpl'
DefaultListableBeanFactory:450 - Creating instance of bean 'ticketServiceImpl'
InjectionMetadata:72 - Registered injected element on class [br.com.xpto.sys.business.impl.TicketServiceImpl]: AutowiredFieldElement for private br.com.xpto.sys.dao.api.TicketDAO br.com.xpto.sys.business.impl.TicketServiceImpl.dao
DefaultListableBeanFactory:523 - Eagerly caching bean 'ticketServiceImpl' to allow for resolving potential circular references
InjectionMetadata:86 - Processing injected element of bean 'ticketServiceImpl': AutowiredFieldElement for private br.com.xpto.sys.dao.api.TicketDAO br.com.xpto.sys.business.impl.TicketServiceImpl.dao
DefaultListableBeanFactory:221 - Creating shared instance of singleton bean 'ticketDAOImpl'
DefaultListableBeanFactory:450 - Creating instance of bean 'ticketDAOImpl'
AnnotationTransactionAttributeSource:108 - Adding transactional method 'TicketDAOImpl.findByTicketNumber' with attribute: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly; ''
InfrastructureAdvisorAutoProxyCreator:538 - Creating implicit proxy for bean 'ticketDAOImpl' with 0 common interceptors and 1 specific interceptors
JdkDynamicAopProxy:115 - Creating JDK dynamic proxy: target source is SingletonTargetSource for target object [br.com.xpto.sys.dao.impl.TicketDAOImpl@2242b3b8]
DefaultListableBeanFactory:478 - Finished creating instance of bean 'ticketDAOImpl'
AutowiredAnnotationBeanPostProcessor:480 - Autowiring by type from bean name 'ticketServiceImpl' to bean named 'ticketDAOImpl'
DefaultListableBeanFactory:478 - Finished creating instance of bean 'ticketServiceImpl'

NPE进入dao.findByTicketId（ticketId）调用。由于dao为null，因此抛出异常。

在我阅读this和this帖后，我尝试做了一些小修改，但没有幸运。

下面我发布了代码的主要部分。欢迎任何建议。

更新

根据要求，我还发布了如何实例化TicketServiceImpl类和堆栈跟踪。

该类在ItemProcessor bean（spring批处理）

中实例化

public class TicketItemProcessor implements ItemProcessor<Ticket, TicketLog> {

    @Override
    public TicketLog process(Ticket item) throws Exception {

        TicketServiceImpl srv = new TicketServiceImpl();
        Ticket t = srv.findByTicketId(item.getIdTicket());

        return new TicketLog();
    }
}

TicketServiceImpl

@Service
public class TicketServiceImpl implements TicketService {

    @Autowired
    private TicketDAO dao;

    @Override
    public Ticket findByTicketId(int ticketId) {
        return dao.findByTicketId(ticketId);
    }
}

TicketDAOImpl

@Repository
public class TicketDAOImpl extends implements TicketDAO {
    @Override
    public Ticket findByTicketId(int ticketId) {
        String jpql = "SELECT t FROM Ticket t WHERE t.id = :ticketId";

        Query query = getSession().createQuery(jpql);
        query.setParameter("ticketId", ticketId);
        query.setMaxResults(1);

        Object obj = query.uniqueResult();
        return (Ticket) obj;
    }
}

TicketDAO

public interface TicketDAO extends DAO<Ticket> {
    Ticket findByTicketId(int ticketId);
}

DAO

public interface DAO<E> extends Serializable {
    List<E> listAll();
}

context.xml中

<?xml version="1.0"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:batch="http://www.springframework.org/schema/batch" xmlns:util="http://www.springframework.org/schema/util" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
    http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
    http://www.springframework.org/schema/jdbc 
    http://www.springframework.org/schema/jdbc/spring-jdbc-4.0.xsd
    http://www.springframework.org/schema/util 
    http://www.springframework.org/schema/util/spring-util-4.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.0.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
    http://www.springframework.org/schema/batch 
    http://www.springframework.org/schema/batch/spring-batch-2.2.xsd">

    <context:annotation-config />
    <context:component-scan base-package="br.com.xpto.sys" />

    <bean id="dbDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
        <property name="url" value="jdbc:sqlserver://server;databaseName=db" />
        <property name="username" value="usr" />
        <property name="password" value="pwd" />
    </bean>

    <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dbDataSource" />
        <property name="packagesToScan" value="br.com.xpto.sys.model.entities" />
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">br.com.xpto.sys.dao.utils.SQLServerDialectOverrider</prop>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.format_sql">true</prop>
                <prop key="hibernate.use_sql_comments">false</prop>
                <prop key="hibernate.connection.release_mode">after_transaction</prop>
            </props>
        </property>
    </bean>

    <tx:annotation-driven transaction-manager="transactionManager" mode="proxy"/>
    <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>

    <bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />

</beans>

堆栈跟踪

AbstractStep:222 - Encountered an error executing step step1 in job job-ProcessTickets
java.lang.NullPointerException
    at br.com.xpto.sys.business.impl.TicketServiceImpl.findByTicketId(TicketServiceImpl.java:83)
    at br.com.xpto.sys.jobs.spring.TicketItemProcessor.process(TicketItemProcessor.java:24)
    at br.com.xpto.sys.jobs.spring.TicketItemProcessor.process(TicketItemProcessor.java:1)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.doProcess(SimpleChunkProcessor.java:126)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.transform(SimpleChunkProcessor.java:293)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.process(SimpleChunkProcessor.java:192)
    at org.springframework.batch.core.step.item.ChunkOrientedTasklet.execute(ChunkOrientedTasklet.java:75)
    at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:395)
    at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
    at org.springframework.batch.core.step.tasklet.TaskletStep$2.doInChunkContext(TaskletStep.java:267)
    at org.springframework.batch.core.scope.context.StepContextRepeatCallback.doInIteration(StepContextRepeatCallback.java:77)
    at org.springframework.batch.repeat.support.RepeatTemplate.getNextResult(RepeatTemplate.java:368)
    at org.springframework.batch.repeat.support.RepeatTemplate.executeInternal(RepeatTemplate.java:215)
    at org.springframework.batch.repeat.support.RepeatTemplate.iterate(RepeatTemplate.java:144)
    at org.springframework.batch.core.step.tasklet.TaskletStep.doExecute(TaskletStep.java:253)
    at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:195)
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:141)
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:64)
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:60)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:151)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:130)
    at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:135)
    at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:301)
    at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:134)
    at org.springframework.core.task.SyncTaskExecutor.execute(SyncTaskExecutor.java:50)
    at org.springframework.batch.core.launch.support.SimpleJobLauncher.run(SimpleJobLauncher.java:127)
    at br.com.xpto.sys.jobs.AppStandalone.run(AppStandalone.java:111)
    at br.com.xpto.sys.jobs.AppStandalone.main(AppStandalone.java:75)