Question

在我的J2EE应用程序中，我尝试使用spring-boot和JPA技术，将EntityManager注入DAO层。但是，我有一些问题......我的用户CRUD存储库：

@Repository
public class UserRepositoryImpl implements UserRepository {

@PersistenceContext(unitName = "data")
private EntityManager entityManager;
// and crud methods
}

我的spring-boot应用程序类：

@SpringBootApplication
public class App {
    public static void main(String [] args) {
        SpringApplication.run(App.class, args);
    }

}

最后我的persistence.xml，位于src / main / resources / META-INF文件夹中：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
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_2_0.xsd">
<persistence-unit name="data" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <class>com.example.domain.User</class>
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
        <property name="hibernate.connection.autocommit" value="false" />
        <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect" />
        <property name="hibernate.c3p0.min_size" value="4" />
        <property name="hibernate.c3p0.max_size" value="128" />
        <property name="javax.persistence.jdbc.url" value="jdbc:sqlserver://localhost:1433;databaseName=qwerty;sendStringParametersAsUnicode=false" />
        <property name="javax.persistence.jdbc.user" value="sa" />
        <property name="javax.persistence.jdbc.driver" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
        <property name="javax.persistence.jdbc.password" value="" />
        <property name="hibernate.hbm2ddl.auto" value="update" />
        <property name="hibernate.show_sql" value="false" />
    </properties>
</persistence-unit>

因此，当我尝试使用这个注入的entityManager时，我得到NullPointerException。注入其他@Autowired字段没有任何问题。这段代码有什么问题？我需要一些额外的配置吗？我是初学者（甚至不是初级开发人员），我确实对Spring-boot是什么以及如何配置它有一些误解，比如Spring在xml文件中。如果由于注入EM而需要这样的xml配置，请展示如何操作。

UPD2。依赖

<dependencies>
    <!-- logger -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
    </dependency>

    <!-- db -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-c3p0</artifactId>
    </dependency>
    <dependency>
        <groupId>org.javassist</groupId>
        <artifactId>javassist</artifactId>
    </dependency>
    <dependency>
        <groupId>com.microsoft</groupId>
        <artifactId>sqljdbc4</artifactId>
    </dependency>
    <dependency>
        <groupId>org.quartz-scheduler</groupId>
        <artifactId>quartz</artifactId>
        <version>2.2.1</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.5.3</version>
    </dependency>

    <!-- csv -->
    <dependency>
        <groupId>com.opencsv</groupId>
        <artifactId>opencsv</artifactId>
        <version>3.3</version>
    </dependency>

    <!-- spring-boot -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
        <version>1.2.4.RELEASE</version>

        <exclusions>
            <exclusion>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-logging</artifactId>
            </exclusion>
        </exclusions>

    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-log4j</artifactId>
        <version>1.2.4.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-tx</artifactId>
        <version>4.1.6.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>1.2.4.RELEASE</version>

        <exclusions>
            <exclusion>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-logging</artifactId>
            </exclusion>
        </exclusions>

    </dependency>

Answer 1

您应该使用spring-boot-starter-data-jpa

的依赖项

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

要使用持久性xml，您应该按照文档中的说明定义一个bean。

Spring不需要使用XML来配置JPA提供程序，Spring Boot假定您希望利用该功能。如果您更喜欢使用persistence.xml，那么您需要定义自己的@Bean类型为LocalEntityManagerFactoryBean（id为'entityManagerFactory'，并在那里设置持久性单元名称。

http://docs.spring.io/spring-boot/docs/current/reference/html/howto-data-access.html#howto-use-traditional-persistence-xml

或者您可以完全跳过persistence.xml并在application.properties文件中定义连接属性。

从文档中引用

DataSource配置由spring.datasource。*中的外部配置属性控制。例如，您可以在application.properties中声明以下部分：

spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

http://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-sql.html#boot-features-connect-to-production-database

（更改驱动程序和其他数据以匹配您的环境）

祝你好运！

Answer 2

您可以使用java配置来配置jpa持久性。下面的代码显示了配置的示例示例：

@Component
public class JpaConfiguration {

    @Bean
    @Primary
    public DataSource dataSource() {

        final SimpleDriverDataSource dataSource = new SimpleDriverDataSource();
        dataSource.setDriver(new org.postgresql.Driver());
        dataSource.setUrl("jdbc:postgresql://localhost:5432/users"); 
        dataSource.setUsername("postgres");
        dataSource.setPassword("admin");

        return dataSource;
    }

    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter();
        jpaVendorAdapter.setGenerateDdl(true);
        jpaVendorAdapter.setShowSql(true);
        jpaVendorAdapter.setDatabasePlatform("org.hibernate.dialect.PostgreSQLDialect");

        return jpaVendorAdapter;
    }  

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {

        LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean();
        lef.setPackagesToScan("tn.bergit.crud.entity");
        lef.setDataSource(dataSource());
        lef.setJpaVendorAdapter(jpaVendorAdapter());

        Properties properties = new Properties();
        properties.setProperty("hibernate.show_sql", "true");
        properties.setProperty("hibernate.jdbc.fetch_size", "100");
        properties.setProperty("hibernate.hbm2ddl.auto", "update");

        lef.setJpaProperties(properties);
        return lef;
    }    


}

您可以在github上看到此示例（click here）

Answer 3

如果您想继续使用persistence.xml文件，只需在配置类中添加以下代码

    @Bean
public LocalEntityManagerFactoryBean entityManagerFactory(){
    LocalEntityManagerFactoryBean factoryBean = new LocalEntityManagerFactoryBean();
    factoryBean.setPersistenceUnitName("data");
    return factoryBean;
}

Answer 4

如果您使用以下代码，则要求EntityManager的类应该是Spring Bean

public class Foo {
  @PersistenceContext
  private EntityManager entityManager;
}

在这里，如果您使用 new 关键字在上方获得Foo类的实例，则 EntityManager 将为 null 。

>

希望这对某人有帮助！

Spring-boot + JPA EntityManager注入失败

4 个答案: