自动装配不在@Entity类中工作

Question

我有一个名为Menu的类,注释为@Entity,我需要在名为GestoreMessaggi的类中使用一个方法

....    
@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

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

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

什么时候,我打电话给gestoreMessaggi.gest(); 从Menu类,我收到一个错误,因为messageSource为null.gestoreMessaggi istance不为null,仅为messageSource为null

重要提示:只有当我从注释为@Entity的类中调用GestoreMessaggi时,才会在messageSource上获取null .

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

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

谢谢

Answer 1

您可以遵循两种方法:

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,使您的实体成为POJO,无需任何逻辑或依赖注入机制

如果你选择选项1,你必须显式访问Spring的上下文并检索你需要的bean实例:

@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扫描此类才能使其正常工作.

然后,在你的内部@EntityClass,这样做:

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

这就是全部.请注意,你就不需要自动装配GestoreMessaggi成你的@Entity了.另请注意,Spring和大多数社区都不推荐这种方法,因为它将您的域类(您的@Entity类)与Spring类耦合.

如果你选择选项2,那么你需要做的就是让Spring像往常一样解决自动装配,但是在你的实体之外(例如在dao或服务中),如果你的实体需要你填写一些消息或其他什么,只需在其上调用一个setter.(那取决于你的要求,取决于你@Entity的属性@Transient与否取决于你).