引用服务类内部的配置类时发生BeanCreationException错误

Question

我正在尝试在@Service类中@Autowire一个@Configuration类。基本上，我的@Configuration类包含到我的自定义.properties文件的映射。当我尝试在服务类中自动连接配置类时，会出现BeanCreationException。我不确定会发生什么。刚刚遵循了关于从spring创建属性类的指南。我一定错过了什么。

此外，当我尝试将@Configuration类自动连接到另一个@Configuration类时，它会顺利运行

目前，我知道prop总是空的，因为当我删除prop.getUploadFileLocation()调用时，一切都会好起来。自动布线时一定出了问题。

这是我的服务类

@Service
public class ImageService {
public static Logger logger = Logger.getLogger(ImageService.class.getName());
@Autowired
MyProperties prop;
private final String FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";
public void upload(String base64ImageFIle) throws IOException {
logger.info(FILE_UPLOAD_LOCATION);
}
}

这是我的配置类

@Data
@Configuration
@ConfigurationProperties (prefix = "my")
public class MyProperties {
private String resourceLocation;
private String resourceUrl;
public String getUploadFileLocation() {
return getResourceLocation().replace("file:///", "");
}
public String getBaseResourceUrl() {
return getResourceUrl().replace("**", "");
}
}

这里是我可以成功使用MyProperties的地方

@Configuration
public class StaticResourceConfiguration implements WebMvcConfigurer {
@Autowired
MyProperties prop;
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler(prop.getResourceUrl())
.addResourceLocations(prop.getResourceLocation());
}
}

Answer 1

问题是您试图使用自动连接字段来设置内联字段分配中的值。

这意味着

private final String FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";

在prop自动连线之前执行，这意味着它将始终为空

缓解这种情况的方法是使用构造函数注入。

@Service
public class ImageService {
//Fine since you are using static method
public static Logger logger = Logger.getLogger(ImageService.class.getName());
//Not needed if you are only using it to set FILE_UPLOAD_LOCATION
//Allows field to be final
private final MyProperties prop;
//Still final
private final String FILE_UPLOAD_LOCATION;
//No need for @Autowired since implicit on component constructors
ImageService(MyProperties prop){
//Again not needed if you aren't going to use anywhere else in the class
this.prop = prop;
FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";
}
public void upload(String base64ImageFIle) throws IOException {
logger.info(FILE_UPLOAD_LOCATION);
}
}

请参阅这个问题，了解为什么在一般中构造函数比@autowired更受欢迎

Answer 2

如果您需要在StaticResourceConfigurationbean之前创建MyPropertiesbean，您可以按如下方式放置@ConditionalOnBean(MyProperties.class)。Spring将在处理StaticResourceConfiguration之前确保存在MyProperties。

@Configuration
@ConditionalOnBean(MyProperties.class)
public class StaticResourceConfiguration implements WebMvcConfigurer {