为什么实体对象在方法返回后会被分离？ （弹簧数据JPA）

Question

已解决：问题出在环绕方面，它以某种方式修改了代理中的返回值。对不起，无法回答的问题。也许有人知道我的错。感谢您提供有用的答案！

我的 Spring Boot 控制台应用程序有问题。我也在使用 spring data jpa 来坚持。一切正常，我可以保存和查找实体，但是当服务类方法返回一个实体时，它将被分离。当我想使用返回的对象时，应用程序失败，因为对象值为空。

这只是一个例子。

@Entity
@Table(name = "person")
public class Person {

    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    private int id;
    private String name;
    @Convert(converter = LocalDateAttributeConverter.class)
    private LocalDate birth;

    public Person() {
    }
    //getter, setter..
}

public interface PersonRepository extends CrudRepository<Person, Long> {

    public Person findByName(String name);

}

public class Service {

    @Autowired
    private PersonRepository personRepository;

    public Person findPersonByName(String name) {
        return personRepository.findByName(name); // System.out.println(person.name) -> someone
    }
}

public class App {

    private Service service;

    public void doSomething(){
        Person person = service.findPersonByName("someone"); 
        // System.out.println(person.name) -> nullpointerEx
    }
} 

//The player like person in the exaple. I must cover some detail in the package names. 
//This is the real exception. As a say above, the code it's just a raw example. Probably don't match for this.
Hibernate: select player0_.id as id1_7_, player0_1_.email as email2_7_, player0_1_.password as password3_7_, player0_.balance as balance1_4_, player0_.birth as birth2_4_, player0_.currency as currency3_4_, player0_.name as name4_4_ from player player0_ inner join user player0_1_ on player0_.id=player0_1_.id where player0_.name=?

14:24:02.087 [main] INFO  o.s.b.a.l.ConditionEvaluationReportLoggingListener - 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
14:24:02.103 [main] ERROR o.s.boot.SpringApplication - Application run failed
java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:787)
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:768)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:322)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
    at com....Application.main(..Application.java:13)
Caused by: java.lang.NullPointerException: null
    at com.....view.ConsoleView.printWelcomeMassege(ConsoleView.java:101)
    at com.....App.createPersone(App.java:46)
    at com.....App.play(App.java:33)
    at com....Application.lambda$0(..Application.java:22)
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:784)
    ... 5 common frames omitted
14:24:02.118 [main] INFO  o.s.o.j.LocalContainerEntityManagerFactoryBean - Closing JPA EntityManagerFactory for persistence unit 'default'
14:24:02.118 [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Shutdown initiated...
14:24:02.165 [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Shutdown completed.

我该如何处理？

Answer 1

我认为您缺少 @Column(name = "name") 注释

Answer 2

为什么实体对象在方法返回后会被分离？

因为服务未声明为事务性的。

试试：

@Service
**@Transactional**
public class Service {

    @Autowired
    private PersonRepository personRepository;

    public Person findPersonByName(String name) {
        return personRepository.findByName(name); // System.out.println(person.name) -> someone
    }
}

或

@Service
public class Service {

    @Autowired
    private PersonRepository personRepository;

    **@Transactional**
    public Person findPersonByName(String name) {
        return personRepository.findByName(name); // System.out.println(person.name) -> someone
    }
}

要减少注释的数量并降低忘记注释的风险，您还可以使用自定义注释TransactionalService：

**@TransactionalService**
public class Service {

    @Autowired
    private PersonRepository personRepository;

    public Person findPersonByName(String name) {
        return personRepository.findByName(name); // System.out.println(person.name) -> someone
    }
}

TransactionalService 还配置为回滚 BusinessException 及其子类。

库 Drombler Commons 是开源的，可从 Maven Central 获得：

<dependency>
  <groupId>org.drombler.commons</groupId>
  <artifactId>drombler-commons-spring-transaction</artifactId>
  <version>1.0</version>
</dependency>

但是请注意，分离实体不会使它们为空。 访问 name 属性时你真的得到 NullPointerException 吗？这表明无法找到该实体。

但从您的代码示例看来，您从访问未初始化的服务中获得了 NullPointerException。

您需要在 App 类中自动装配 Service 以消除 NullPointerException：

**// Some spring annotation**
public class App {

    **@Autowired**
    private Service service;

    public void doSomething(){
        Person person = service.findPersonByName("someone"); 
        // System.out.println(person.name) -> nullpointerEx
    }
}