java - Spring 注入(inject)失败？

Question

我有这个代码:

    private ServiceLayer serviceLayer;  
    @RequestMapping(value = { "/process" }, method = RequestMethod.GET)
    public String processMessaging(HttpServletRequest request) 
    {
        return serviceLayer.getMd5Hash();

    }

服务层

@Autowired
    public ServiceLayer() {
    }

问题是，当我运行项目时，Md5Hash 为空，serviceLayer 实例也为空，似乎没有调用 Constructor。

当我改用下面的代码时，它工作正常:

@Autowired
    private ServiceLayer serviceLayer;

ServiceLayer 使用 @Component 注释。

然后 serviceLayer 的实例不为 null 但 md5Hash 为 null。我最近学习了 Spring Injections 的概念，但它没有按预期工作。有人请告诉我该怎么办？

已编辑

它在我创建 Property Autowired 而不是构造函数时运行。但是为什么它不能与使用或不使用 init() 方法 Autowiring 的构造函数一起工作。

我尝试按照“Link”的建议将 md5Hash 方法作为 Bean，但这让我陷入了另一个错误。

Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.lang.String com.orange.raidar.backend.controller.raidarDummyController.md5Hash; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'getMD5hash' defined in class path resource [com/orange/raidar/backend/filter/ServiceLayer.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [java.lang.String]: Factory method 'getMD5hash' threw exception; nested exception is java.lang.IllegalStateException: No thread-bound request found: Are you referring to request attributes outside of an actual web request, or processing a request outside of the originally receiving thread? If you are actually operating within a web request and still receive this message, your code is probably running outside of DispatcherServlet/DispatcherPortlet: In this case, use RequestContextListener or RequestContextFilter to expose the current request.
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)

我现在尝试的是:

@Bean
    public String mD5Hash() {
        md5Hash = MD5Generator.getMd5HashCode(httpRequestToString());
        return md5Hash;

    }

在 Controller 中

@Autowired
    private String md5Hash;

Answer 1

init() 中初始化的 Md5Hash 可能超出范围。更好的策略是拥有这样的东西

@Component
public class ServiceLayer() {

    @Autowired
    private String md5Hash;

    // Some other code
}

然后声明一个bean

@Bean
public String md5Hash() {
    // Some code
    return md5HashString;
}

在一些@Config文件中声明