無法實例化bean類：找不到默認構造函數;嵌套的例外是java.lang.NoSuchMethodException

Question

我試圖@Autowired一類，這是一個簡單的類，沒有註釋，只是其中有一些計算類。然而，當我嘗試@Autowired這個類，在我的控制，我得到了以下錯誤：

控制器：

public class MyClass { 

public Double calculation(){ 
     //implementation 
    } 

} 

錯誤：

Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private net.pontoall.hemisphere.core.calculo.evaportranspiracao.MyClass net.pontoall.hemisphere.controller.LeituraController.evapo; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [net.pontoall.hemisphere.core.calculo.evaportranspiracao.MyClass] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} 
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:513) 
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:92) 
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:284) 
... 21 more 
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [net.pontoall.hemisphere.core.calculo.evaportranspiracao.MyClass] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:948) 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:817) 
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:731) 
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:485) 
... 23 more 

@Controller 
public class LeituraController extends HemisphereController { 

private static final String VIEW = "calculation/index"; 

@Autowired 
private MyClass evapo; 

@RequestMapping(value = "/request", method = RequestMethod.GET) 
@SuppressWarnings("unchecked") 
public ModelAndView leituras() { 
    ModelAndView view = new ModelAndView(VIEW); 
    Double valorMax = evapo.calculation(); 
    return view; 
}} 

類的實例

有人可以幫助我嗎？謝謝。

Answer 1

注入的MyClass實例必須是Spring bean。用@Component或其他bean註釋標註它，或者在spring XML配置文件中聲明它。