7

我使用 JPA 为我的 DAO 类编写测试，Hibernate 作为 JPA 提供者，以及 Spring 3.2。我无法正确注入实体管理器，尝试访问它时出现 NullPointerException。我的 GenericDAO 实现如下所示：

@Repository
public class GenericDAOImpl implements GenericDAO {

    @PersistenceContext(unitName="unitname")
    private EntityManager entityManager;

    public EntityManager getEntityManager() {
        return entityManager;
    }


    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    // NullPointerException when calling this, entityManager is null
    public Query createNamedQuery(String name) {
        return entityManager.createNamedQuery(name);
    }        

    // many other methods....
}

测试的类如下所示：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = { "/com/main/resources/root-context.xml", "/com/main/resources/servlet-context.xml"})
public class TestModel {

    @Before
    public void setUp() throws Exception{
        ...
    }

    @Test
    public void test(){
        ...
    }
}

我的 root-context.xml 如下：

<?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:aop="http://www.springframework.org/schema/aop"
    xmlns:beans="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context-3.0.xsd 
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd        
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
        "
>

    <!-- Root Context: defines shared resources visible to all other web components -->

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="username" value="root" />
        <property name="password" value="root" />
    </bean>

    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="persistenceUnitName" value="unitname" />
        <property name="dataSource" ref="dataSource" />
        <property name="packagesToScan" value="com.main" />
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="showSql" value="true" />
                <property name="generateDdl" value="false" />
                <property name="databasePlatform" value="org.hibernate.dialect.MySQL5Dialect" />
            </bean>
        </property>
    </bean>

    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>

    <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />



    <tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="false" />
    <context:component-scan base-package="com.main" />
    <context:annotation-config />

</beans>

我尝试了几种方法都没有成功，甚至按照其他 SO 问题中的建议添加了 PersistenceAnnotationBeanPostProcessor。所有其他事情似乎都工作正常：Hibernate 创建数据库表，加载上下文等。我做错了什么？

编辑：堆栈跟踪如下：

java.lang.NullPointerException
    at com.main.model.dao.JPAImpl.GenericDAOImpl.createNamedQuery(GenericDAOImpl.java:119)
    at com.main.model.bo.DescriptorBO.persist(DescriptorBO.java:52)
    at com.main.webmodule.JSONSerializer.deserialize(JSONSerializer.java:149)
    at com.main.tests.TestModel.test(TestModel.java:86)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:88)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

这是persistence.xml：

<?xml version="1.0" encoding="UTF-8"?><persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
    <persistence-unit name="unitname" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <mapping-file>META-INF/jpql/NamedQueries.xml</mapping-file>


        <class>com.main.model.Account</class>
        <class>com.main.model.Action</class>
        <class>com.main.model.Device</class>
        <class>com.main.model.DeviceDescriptor</class>
        <class>com.main.model.Event</class>
        <class>com.main.model.File</class>
        <class>com.main.model.Rule</class>
        <class>com.main.model.StateVar</class>
        <class>com.main.model.Argument</class>
        <exclude-unlisted-classes>false</exclude-unlisted-classes> 


        <properties>

            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value="root"/>
            <property name="hibernate.connection.provider_class" value="org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider" />
            <property name="hibernate.connection.autocommit" value="true"/>
            <property name="hibernate.connection.release_mode" value="auto"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://127.0.0.1:3306/testweb"/>
            <property name="hibernate.hbm2ddl.auto" value="create"/>

            <property name="hibernate.c3p0.min_size" value="1" />
            <property name="hibernate.c3p0.max_size" value="10" />
            <property name="hibernate.c3p0.acquire_increment" value="1" />
            <property name="hibernate.c3p0.idle_test_period" value="300" />
            <property name="hibernate.c3p0.max_statements" value="0" />
            <property name="hibernate.c3p0.timeout" value="100" />

            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>

        </properties>




    </persistence-unit>
</persistence>
4

2 回答 2

10

我终于设法解决了这个问题。为了实例化 GenericDAO，我使用了自动装配注解，这样：

@Autowired
private GenericDAO genericDao;

但是发生这种情况的类，称为 DescriptorBO，是这样实例化的：

DescriptorBO descrBO = new DescriptorBO(...);

从而完全摆脱了Spring容器的控制。将其更改为：

@Autowired
private DescriptorBO descrBO;

并将适当的 bean 定义添加到 root-context.xml：

<bean name="descriptorBO" class="com.main.model.bo.DescriptorBO">
    <property name="genericDao" ref="genericDao" />
</bean>

<bean name="genericDao" class="com.main.model.dao.JPAImpl.GenericDAOImpl" />

解决了这个问题。现在 EntityManager 已正确注入。

经验教训：如果 Spring 不注入 EntityManager（或任何其他注入对象），请检查对象之上的所有对象层次结构是否由 Spring 管理，即直接或使用 Autowired 注释从应用程序上下文中的 beans 实例化。检查您是否没有使用 new 运算符来实例化任何这些对象！

于 2013-05-08T10:27:34.397 回答
0

如果有人会来这里寻求正确答案：

要在 Spring bean 中自动装配 EntityManger 而无需调用 EntityManagerFactory.createEntityManager()，您需要将PersistenceAnnotationBeanPostProcessor bean 添加到您的配置中：

....
xmlns:jpa="http://www.springframework.org/schema/data/jpa"
xsi:schemaLocation="http://www.springframework.org/schema/data/jpa
                    http://www.springframework.org/schema/data/jpa/spring-jpa.xsd"
...

<jpa:repositories base-package="com.galera" />
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>
 
...

<!-- Let's forget about Maven -->   

<dependency>
  <groupId>org.springframework.data</groupId>
  <artifactId>spring-data-jpa</artifactId>
</dependency>

之后，EntityManager 的自动装配就可以正常工作了！

@Autowire
EntityManager entityManager; // Magic (*_*)
于 2021-11-17T17:41:47.973 回答