将外化值注入Spring注释 [英] Injecting externalized value into Spring annotation

问题描述

我一直在考虑在编译时评估注释值的Java功能，它似乎真的难以外化注释值。

I've been thinking around the Java feature that evaluates annotation values in compile-time and it seems to really make difficult externalizing annotation values.

然而，我是不确定它是否真的不可能，所以我很感激任何建议或明确的答案。

However, I am unsure whether it is actually impossible, so I'd appreciate any suggestions or definitive answers on this.

更重要的是，我试图外化一个控制的注释值Spring中预定方法调用之间的延迟，例如：

More to the point, I am trying to externalize an annotation value which controls delays between scheduled method calls in Spring, e.g.:

public class SomeClass {

    private Properties props;
    private static final long delay = 0;

    @PostConstruct
    public void initializeBean() {
        Resource resource = new ClassPathResource("scheduling.properties");
        props = PropertiesLoaderUtils.loadProperties(resource);
        delay = props.getProperties("delayValue");
    }

    @Scheduled(fixedDelay = delay)
    public void someMethod(){
        // perform something
    }
}

假设 scheduling.properties 在类路径上并包含属性键 delayValue 及其对应的long值。

Suppose that scheduling.properties is on classpath and contains property key delayValue along with its corresponding long value.

现在，这段代码有明显的编译错误，因为我们是尝试将值赋给 final 变量，但这是必需的，因为我们无法将变量赋值给注释值，除非它是 static final 。

Now, this code has obvious compilation errors since we're trying to assign a value to final variable, but that is mandatory, since we can't assign the variable to annotation value, unless it is static final.

有没有办法解决这个问题？我一直在考虑Spring的自定义注释，但根本问题仍然存在 - 如何将外化值分配给注释？

Is there any way of getting around this? I've been thinking about Spring's custom annotations, but the root issue remains - how to assign the externalized value to annotation?

欢迎任何想法。

编辑：一个小更新 - 对于这个例子，Quartz集成是过度的。我们只需要以亚分钟的分辨率进行定期执行即可。

A small update - Quartz integration is overkill for this example. We just need a periodic execution with sub-minute resolution and that's all.

推荐答案

@Scheduled < Spring v3.2.2中的/ code>注释已将String参数添加到原始的3个长参数中以处理此问题。 fixedDelayString ， fixedRateString 和 initialDelayString 现在也可用：

 @Scheduled(fixedDelayString = "${my.delay.property}")
 public void someMethod(){
        // perform something
 }

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