spring - 如何在类级变量中使用 Spring @Value 注解

Question

我需要在类的实例变量中使用 @Value 注入(inject)的参数，并且可以在其所有子类中重用该变量。

   @Value(server.environment)
   public String environment;

   public String fileName = environment + "SomeFileName.xls";

这里的问题是先初始化文件名​​，然后进行环境注入(inject)。所以我总是得到 null-SomeFileName.xls。

总之要在spring中初始化第一个@Value。

Answer 1

因此，您可以使用 @PostConstruct。来自 documentation :

The PostConstruct annotation is used on a method that needs to be executed after dependency injection is done to perform any initialization.

@PostConstruct 允许您在设置属性后执行修改。一种解决方案是这样的:

public class MyService {

    @Value("${myProperty}")
    private String propertyValue;

    @PostConstruct
    public void init() {
        this.propertyValue += "/SomeFileName.xls";
    }

}

另一种方法是使用 @Autowired 配置方法。来自 documentation :

Marks a constructor, field, setter method or config method as to be autowired by Spring's dependency injection facilities.

...

Config methods may have an arbitrary name and any number of arguments; each of those arguments will be autowired with a matching bean in the Spring container. Bean property setter methods are effectively just a special case of such a general config method. Such config methods do not have to be public.

例子:

public class MyService {

    private String propertyValue;

    @Autowired
    public void initProperty(@Value("${myProperty}") String propertyValue) {
        this.propertyValue = propertyValue + "/SomeFileName.xls";
    }

}

不同之处在于，使用第二种方法时，您的 bean 没有额外的钩子(Hook)，您可以在 Autowiring 时对其进行调整。