Spring中的事务和流 [英] Transactional and Stream in Spring

问题描述

我试着理解为什么这段代码不起作用

I try to understand why this code doesn't work

在组件中：

@PostConstruct
public void runAtStart(){

    testStream();
}

@Transactional(readOnly = true)
public void testStream(){
    try(Stream<Person> top10ByFirstName = personRepository.findTop10ByFirstName("Tom")){
        top10ByFirstName.forEach(System.out::println);
    }
}

和存储库：

public interface PersonRepository extends JpaRepository<Person, Long> {
    Stream<Person> findTop10ByFirstName(String firstName);
}

我得到：

org.springframework.dao.InvalidDataAccessApiUsageException：您正在尝试执行流式查询方法，而没有保持连接打开的周围事务，以便实际可以使用Stream。确保使用流的代码使用@Transactional或任何其他方式声明（只读）事务。

org.springframework.dao.InvalidDataAccessApiUsageException: You're trying to execute a streaming query method without a surrounding transaction that keeps the connection open so that the Stream can actually be consumed. Make sure the code consuming the stream uses @Transactional or any other way of declaring a (read-only) transaction.

推荐答案

Spring的一个关键点是许多带注释的功能使用代理来提供注释功能。那是 @Transactional ， @Cacheable 和 @Async 全部依赖于Spring检测那些注释并将这些bean包装在代理bean中。

One key thing about Spring is that many annotated features use proxies to provide the annotation functionality. That is @Transactional, @Cacheable and @Async all rely on Spring detecting those annotations and wrapping those beans in a proxy bean.

在这种情况下，代理方法只能在调用时使用班级，而不是来自 班级。请参阅此关于这个话题。

That being the case, a proxied method can only be used when invoked on the class and not from within the class. See this about the topic.

尝试：

1. 重构并称之为 @Transactional 来自您上下文中其他类的方法，或


2. 按自动装配类本身并以这种方式调用 @Transactional 方法。

1. Refactoring and call this @Transactional method from another class in your context, or
2. By self-autowiring the class into itself and calling the @Transactional method that way.

演示（1）：

public class MyOtherClass {

    @Autowired
    private MyTestStreamClass myTestStreamClass;

    @PostConstruct
    public void runAtStart(){
        // This will invoke the proxied interceptors for `@Transactional`
        myTestStreamClass.testStream();
    }

}

演示（2 ）：

@Component
public class MyTestStreamClass {

   @Autowired
   private MyTestStreamClass myTestStreamClass;

   @PostConstruct
   public void runAtStart(){
       // This will invoke the proxied interceptors for `@Transactional` since it's self-autowired
       myTestStreamClass.testStream();
   }

   @Transactional(readOnly = true)
   public void testStream(){
       try(Stream<Person> top10ByFirstName = personRepository.findTop10ByFirstName("Tom")){
               top10ByFirstName.forEach(System.out::println);
           }
   }
}

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