有没有办法@Autowire 一个需要构造函数参数的bean?

问题描述

我正在使用 Spring 3.0.5，并且尽可能为我的班级成员使用 @Autowire 注释.我需要自动装配的 bean 之一需要为其构造函数提供参数.我已经浏览了 Spring 文档，但似乎找不到任何关于如何注释构造函数参数的参考.

I'm using Spring 3.0.5 and am using @Autowire annotation for my class members as much as possible. One of the beans that I need to autowire requires arguments to its constructor. I've looked through the Spring docs, but cannot seem to find any reference to how to annotate constructor arguments.

在 XML 中，我可以将其用作 bean 定义的一部分.@Autowire注解有类似的机制吗?

In XML, I can use as part of the bean definition. Is there a similar mechanism for @Autowire annotation?

例如:

@Component
public class MyConstructorClass{

  String var;
  public MyConstructorClass( String constrArg ){
    this.var = var;
  }
...
}


@Service
public class MyBeanService{
  @Autowired
  MyConstructorClass myConstructorClass;

  ....
}

在这个例子中，如何使用@Autowire 注释在 MyBeanService 中指定constrArg"的值?有没有办法做到这一点?

In this example, how do I specify the value of "constrArg" in MyBeanService with the @Autowire annotation? Is there any way to do this?

谢谢，

埃里克

推荐答案

您需要 @Value 注释.

You need the @Value annotation.

一个常见的用例是使用"#{systemProperties.myProp}" 样式表达式.

public class SimpleMovieLister {

  private MovieFinder movieFinder;
  private String defaultLocale;

  @Autowired
  public void configure(MovieFinder movieFinder,
                        @Value("#{ systemProperties['user.region'] }") String defaultLocale) {
      this.movieFinder = movieFinder;
      this.defaultLocale = defaultLocale;
  }

  // ...
}

参见: 表达式语言 >注解配置

更明确地说:在您的场景中，您将连接两个类，MybeanService 和 MyConstructorClass，如下所示:

To be more clear: in your scenario, you'd wire two classes, MybeanService and MyConstructorClass, something like this:

@Component
public class MyBeanService implements BeanService{
    @Autowired
    public MybeanService(MyConstructorClass foo){
        // do something with foo
    }
}

@Component
public class MyConstructorClass{
    public MyConstructorClass(@Value("#{some expression here}") String value){
         // do something with value
    }
}

更新:如果您需要多个具有不同值的 MyConstructorClass 实例，您应该使用限定符注解

Update: if you need several different instances of MyConstructorClass with different values, you should use Qualifier annotations

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