Java 如何创建自定义 @ConditionalOnProperty 以简化使用

您可以使用@ConditionalOnProperty为@OnMyServiceVersion批注添加注释，并将批注的value作为havingValue属性@ConditionalOnProperty的别名:

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@ConditionalOnProperty(prefix = "myservice", name = "implversion")
public @interface OnMyServiceVersion {

    @AliasFor(annotation = ConditionalOnProperty.class, attribute = "havingValue")
    String value() default "";

}

以下是一个完整的示例，它实际展示了这一点:

package com.example.demo;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Service;

@SpringBootApplication
public class CustomPropertyConditionApplication {

    public static void main(String[] args) {
        SpringApplication.run(CustomPropertyConditionApplication.class, "--myservice.implversion=b");
    }
    
    @Service
    @OnMyServiceVersion("a")
    static class ServiceA {
        
        ServiceA() {
            System.out.println("Service A");
        }
        
    }
    
    @Service
    @OnMyServiceVersion("b")
    static class ServiceB {
        
        ServiceB() {
            System.out.println("Service B");
        }
        
    }
    
    @Documented
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ ElementType.TYPE, ElementType.METHOD })
    @ConditionalOnProperty(prefix = "myservice", name = "implversion")
    static @interface OnMyServiceVersion {
        
        @AliasFor(annotation = ConditionalOnProperty.class, attribute = "havingValue")
        String value() default "";
        
    }

}

这将在运行时输出Service B.如果将Main方法中的参数更改为--myservice.implversion=a，它将输出Service A.如果删除该参数，它也不会输出.