自动装配不能在类@Entity中工作 [英] Autowired not working in a Class @Entity

问题描述

我有一个名为 Menu 的类，其标注为 @Entity ，在该类中，我需要在名为 GestoreMessaggi

I have a class called Menu, annnotated as @Entity where i need to use a method inside a class called GestoreMessaggi

....    
@Component
@Entity
@Table(name="menu")
public class Menu implements Serializable{

@Autowired
@Transient // because i dont' save this field on the DB
private GestoreMessaggi gestoreMessaggi;
.....
public void setCurrentLanguage(){

   /* I got the error both if use gestoreMessaggi
   this way and if I use the autowired istance of GestoreMessaggi*/
   GestoreMessaggi gestoreMessaggi = new GestoreMessaggi();  
   gestoreMessaggi.gest();        
}
.....

这是GestoreMessaggi类的相关代码

This is the relevant code of the class GestoreMessaggi

 @Component
    public class GestoreMessaggi {    
        @Autowired 
        private ReloadableResourceBundleMessageSource messageSource;

        public void gest(){
        messageSource.doSomething() <--- here messageSource is null
        }
  }

什么时候，我叫gestoreMessaggi.gest();从Menu类收到错误，因为 messageSource 为空. gestoreMessaggi距离不为null，仅 messageSource

When, I call gestoreMessaggi.gest(); from Menu class, I got an error because messageSource is null. The gestoreMessaggi istance is NOT null, is null just messageSource

重要:仅当我从标注为 @Entity 的类中调用GestoreMessaggi时，messageSource上为null.

IMPORTANT: I get null on messageSource only when I call GestoreMessaggi from classes annotated as @Entity.

在ds-servlet.xml中，我告诉Spring扫描包含Menu和GestoreMessaggi类的包装:

In ds-servlet.xml I tell Spring to scan the pakages that contain Menu and GestoreMessaggi classes:

//Menu package 
<context:component-scan base-package="com.springgestioneerrori.model"/>
//Gestore messaggi package
<context:component-scan base-package="com.springgestioneerrori.internazionalizzazione"/>   

谢谢

推荐答案

您可以采用两种方法:

1. 尝试从@Entity类的方法中获取Spring管理的bean的实例
2. 按照@Stijn Geukens的建议更改设计，并使您的实体成为POJO，而没有任何逻辑或依赖项注入机制

1. Try to get an instance of a Spring-managed bean from within a method of your @Entity class
2. Change the design as suggested by @Stijn Geukens and make your entity a POJO without any logic or dependency injection machanisms

如果选择选项1，则必须显式访问Spring的上下文并检索所需的bean实例:

If you go by option 1, you have to explicitly access Spring's context and retrieve an instance of the bean you need:

@Component
public class Spring implements ApplicationContextAware {

    private static final String ERR_MSG = "Spring utility class not initialized";

    private static ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        context = applicationContext;   
    }

    public static <T> T bean(Class<T> clazz) {
        if (context == null) {
            throw new IllegalStateException(ERR_MSG);
        }
        return context.getBean(clazz);
    }

    public static <T> T bean(String name) {
        if (context == null) {
            throw new IllegalStateException(ERR_MSG);
        }
        return (T) context.getBean(name);
    }
}

您需要让Spring扫描此类，以使其正常工作.

You need to make Spring scan this class in order for this to work.

然后在您的@EntityClass内部，执行以下操作:

Then, inside your @EntityClass, do this:

public void setCurrentLanguage(){
    GestoreMessaggi gestoreMessaggi = Spring.bean(GestoreMessaggi.class);
    gestoreMessaggi.gest();        
}

仅此而已.请注意，您不再需要将GestoreMessaggi自动接线到@Entity中.另请注意， Spring和大多数社区都不推荐这种方法，因为它会将您的域类(您的@Entity类)耦合到Spring类.

And that would be all. Note that you wouldn't need to autowire GestoreMessaggi into your @Entity any more. Please also note that this approach is not recommended neither by Spring nor by most of the community, since it couples your domain classes (your @Entity class) to Spring classes.

如果您选择选项2，那么您所需要做的就是让Spring像往常一样解决自动装配问题，但要在实体之外 (即在dao或服务中)以及您的实体进行自动装配需要您用一些消息或其他内容来填充它，只需在其上调用一个setter. (然后由您决定是否将@Entity s属性设置为@Transient，具体取决于您的要求.)

If you go by option 2, then all you need to do is let Spring resolve the autowiring as usual, but outside of your entity (i.e. in a dao or service), and if your entity needs you to fill it with some message or whatever, just invoke a setter on it. (Then it's up to you to make your @Entitys attribute @Transient or not, depending on your requirements).

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