Vraptor3中依賴注入的問題

Vraptor3聲稱：

Spring Integration

VRaptor works inside Spring and uses ApplicationContext from your application once available. Then, all the Spring functionalities and modules work with VRaptor without any VRaptor configuration.

其實並不是如此，有這樣的問題：

當一個類同時又無參數構造函數及有參數構造函數時，使用Spring的@Autowired會獲得空值，且不會拋出注入失敗的異常。示例代碼以下（來自JForum3裏的代碼）：

public class Category implements Serializable {

    public  Category(){} 

    @Autowired
    public Category(CategoryRepository repository) {
        this.repository = repository;
    }

}

這段代碼裏，repository 一直是null。

緣由是：

Vraptor3用br.com.caelum.vraptor.ioc.spring.InjectionBeanPostProcessor覆蓋了Spring中註解織入的方法org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor

代碼以下：

class InjectionBeanPostProcessor extends AutowiredAnnotationBeanPostProcessor {
    //  in case we are required to change the injection annotation:
    //  public InjectionBeanPostProcessor() {
    //      this.setAutowiredAnnotationType(In.class);
    //  }

@Override
@SuppressWarnings({ "unchecked", "rawtypes" })
public Constructor[] determineCandidateConstructors(Class beanClass, String beanName) throws BeansException {
        Constructor[] candidates = super.determineCandidateConstructors(beanClass, beanName);
        if (candidates == null) {
            Constructor constructor = checkIfThereIsOnlyOneNonDefaultConstructor(beanClass);
            if (constructor != null) {
                candidates = new Constructor[]{constructor};
            }
        }
        return candidates;
    }


@SuppressWarnings({ "rawtypes" })
private Constructor checkIfThereIsOnlyOneNonDefaultConstructor(Class beanClass) {
        Constructor[] constructors = beanClass.getDeclaredConstructors();
        if (constructors.length == 1) {
            if (constructors[0].getParameterTypes().length > 0) {
                return constructors[0];
            }
        }
        return null;
    }
}

簡單粗暴的判斷被注入類的構造函數數量，若是有多個構造函數，直接返回null。因此你會發現明明寫了注入，也沒有報錯，但就是沒值。