Question

在这个例子中，有两个注入的类，EntityManager和UserTransaction。我不明白为什么UserTransaction可以直接注入而不先注释它，但是EntityManager必须在一个单独的类中用@Produces定义和注释？

提前致谢。

CarManager.java

public class CarManager {
@Inject
private EntityManager em;

@Inject
private UserTransaction utx;

private Long id;

private Logger log = Logger.getLogger(CarManager.class.getSimpleName());

public void setId(Long id) {
    this.id = id;
}

/**
 * Returns either a new instance or a managed instance of {@link Car}.
 * The produced entity should be dependent scoped to avoid incompatible proxies between
 * JPA and CDI.
 */
@Produces
public Car getCar() {
    if (id == null) {
        log.info("Returning new instance of Car");
        return new Car();
    }
    log.info("Finding instance of Car with id " + id);
    return em.find(Car.class, id);
}

...
}

EntityManagerProducer.java

public class EntityManagerProducer {
@Produces
@PersistenceContext
private EntityManager em;
}

Answer 1

因为UserTransaction被称为预定义bean，EntityManager因此不需要拥有自己的生成器。有关预定义bean的列表，请参阅25.4 Using Predefined Beans in CDI Applications。

两个类的依赖注入和@Produces注释

1 个答案: