java - 设置后的属性始终为nil

Question

我在 osx 上的 Eclipse 中使用 spring 版本 3.0.6，并且不明白为什么我无法为 bean 设置任何属性。部分代码:

@Component("desktopBuilderCallback")
@Scope("prototype")
public class DesktopBuilderCallback implements BuilderCallback {

  private Socket desktopSocket;

  @Override
  public Transformation afterTransform(Transformation transformation)
      throws Exception {

           \\ some implementation
  }


  @Override
  public void handleStatusUpdate(Transformation transformation)
      throws Exception
      {
       \\ some implementation
      }


  public Socket getDesktopSocket() {
    return desktopSocket;
  }

  public void setDesktopSocket(Socket desktopSocket) {
    this.desktopSocket = desktopSocket;
  }
}


@Component("transformationBuilder")
@Scope("prototype")
public class TransformationBuilder implements Runnable,
SourceNotificationCallback, TargetNotificationCallback,
ApplicationContextAware {

   int test;
   BuilderCallback builderCallback;

   public BuilderCallback getBuilderCallback() {
      return builderCallback;
   }

   public void setBuilderCallback(BuilderCallback builderCallback) {
      this.builderCallback = builderCallback;
   }

   public int getTest() {
      return this.test;
   }

  public void setTest(int theTest) {
      this.test = theTest;
  }
}

public static void main(String[] args) throws IOException {

    TransformationBuilder transformationBuilder = (TransformationBuilder) ctx.getBean("transformationBuilder");

    DesktopBuilderCallback callback = (DesktopBuilderCallback) ctx.getBean("desktopBuilderCallback");
    transformationBuilder.setBuilderCallback(callback);  
    transformationBuilder.setTest(5);
}

代码执行后，test和builderCallback不会被初始化。 test 将为 0，builderCallback 为 nil。不知道怎么可能，我是java和spring的新手...，但我检查过调试器跳转到setter(setTest，setBuilderCallback)，也许是因为项目是为JRE 1.5开发的，但我使用 1.8...

Answer 1

根据您迄今为止发布的代码，我猜测您的问题与 bean 的范围设置为 prototype 有关。

来自spring docs :

The non-singleton, prototype scope of bean deployment results in the creation of a new bean instance every time a request for that specific bean is made (that is, it is injected into another bean or it is requested via a programmatic getBean() method call on the container). As a rule of thumb, you should use the prototype scope for all beans that are stateful, while the singleton scope should be used for stateless beans.

每次您从应用程序上下文中获取 transformationBuilder bean (ctx.getBean("transformationBuilder")) 时，您都会获得一个新实例<TransformationBuilder 的/strong>。在这些实例中，不属于标准 bean 初始化过程一部分的每个手动初始化都将不可用。

要正确初始化您的 bean，您可以使用 @Value 注释从配置中注入(inject)值，使用 @Autowired 注入(inject)其他 bean 实例，或使用 @PostConstruct 方法来执行额外的、重要的初始化。

对于您的类(class)，这可能如下所示:

@Component("transformationBuilder")
@Scope("prototype")
public class TransformationBuilder implements Runnable,
        SourceNotificationCallback, TargetNotificationCallback,
        ApplicationContextAware {

   // either use the value of the property 'some.property.key' or 5 as default
   @Value("${some.property.key:5}")
   int test;

   @Autowired
   @Qualifier("desktopBuilderCallback")
   BuilderCallback builderCallback;

   ...
}

当然，您也可以使用singleton范围(实际上是spring bean的默认范围)。这将导致每次请求此 bean 时 spring 返回相同的实例。但对于 singleton 范围，bean 的初始化也应该由 DI 容器处理。