Question

尝试通过注释case

访问

 handler = new Handler(); 

handler.post(new Runnable() {
            @Override
            public void run() {
                alertDialog.show();
            }
        });

时，我收到NullPointerException

EntityManager

路径PersistenceContext中的我的import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.criteria.CriteriaBuilder; import javax.persistence.criteria.CriteriaQuery; @Stateless public class UserService { @PersistenceContext(unitName = "jcrdb") private EntityManager em; ... }：

persistence.xml

src/main/webapp/META-INF - 班级：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0"
    xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
    <persistence-unit name="jcrdb" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <!-- <jta-data-source>jdbc/jcrdb</jta-data-source> -->
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.format_sql" value="true" />
            <!-- this tell Hibernate to update the DDL when it starts, very useful 
                for development, dangerous in production -->
            <property name="hibernate.hbm2ddl.auto" value="update" />
            <property name="javax.persistence.logging.level" value="INFO" />
            <property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://127.0.0.1:5432/jcrdb" />
            <property name="javax.persistence.jdbc.user" value="jcr_admin" />
            <property name="javax.persistence.jdbc.password" value="q1w2e3r4" />
            <!-- <property name="tomee.jpa.factory.lazy" value="true" />-->
        </properties>
    </persistence-unit>
</persistence>

直接获取EntityManager没有问题：

User

我试过在码头和tomEE中运行它。

在我看来，ejb-stuff并不起作用。我在这里想念的是什么（对这一切都不熟悉）？

Answer 1

如果持久单元是 RESOURCE_LOCAL ，则必须使用

EntityManagerFactory 。

@PersistenceUnit    
private EntityManagerFactory emf;

您可以参考this问题和答案以获取完整的详细信息。

Answer 2

你在哪里拿起那个persistence.xml档案？我知道如果你的配置是用java（而不是XML配置）

，你可以如何选择它

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean()
{
LocalContainerEntityManagerFactoryBean factory =
new LocalContainerEntityManagerFactoryBean();
factory.setPersistenceXmlLocation(
"classpath:...../persistence.xml"
);
//factory.setPersistenceUnitName("whatever");
factory.setJpaVendorAdapter(new HibernateJpaVendorAdapter());
factory.setDataSource(this.springJpaDataSource());
return factory;
}

您还需要设置DataSource：

@Bean
public DataSource springJpaDataSource()
{
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setUrl("jdbc:mysql://localhost/ABCXYZ");
dataSource.setUsername("tomcatUser");
dataSource.setPassword("password1234");
return dataSource;
}

此外，您需要在配置文件

上添加@EnableTransactionManagement注释

如果你想摆脱persistence.xml并且需要在java中完全进行持久化配置，那么你需要在上面替换，返回LocalContainerEntityManagerFactoryBean：

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean()
{
Map<String, Object> properties = new Hashtable<>();
properties.put("javax.persistence.schema-generation.database.action",
"none");
HibernateJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();
adapter.setDatabasePlatform("org.hibernate.dialect.MySQL5InnoDBDialect");
LocalContainerEntityManagerFactoryBean factory =
new LocalContainerEntityManagerFactoryBean();
factory.setJpaVendorAdapter(adapter);
factory.setDataSource(this.springJpaDataSource());
factory.setPackagesToScan("com.wrox.site.entities");
factory.setSharedCacheMode(SharedCacheMode.ENABLE_SELECTIVE);
factory.setValidationMode(ValidationMode.NONE);
Configuring Persistence in Spring Framework ❘ 605
factory.setJpaPropertyMap(properties);
return factory;
}

Answer 3

有时发生这种情况是因为PersistenceAnnotationBeanPostProcessor未由Spring注册。要解决此问题，您可以按如下所示手动定义它：

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

默认的PersistenceAnnotationBeanPostProcessor将由<context:annotation-config/>和<context:component-scan/> XML标签注册。

PersistenceContext没有注入EntityManager

3 个答案: