如何创建自定义注解替代@ConditionalOnProperty简化Spring Boot Bean加载控制？

在Spring Boot项目中，原本通过@ConditionalOnProperty注解根据配置项myservice.implversion的值（如a、b）选择加载MyService接口的不同实现类，示例代码如下：

@ConditionalOnProperty(
    prefix = "myservice",
    name = "implversion",
    havingValue = "a"
)
@Service
public class MyServiceImplA implements MyService {
   // ...
}

现在希望简化为更易用的自定义注解@OnMyServiceVersion，用法示例：

@OnMyServiceVersion(value = "a")
@Service
public class MyServiceImplA implements MyService {
   // ...
}

之前遇到的问题 #

• 尝试用@Conditional配合Condition接口，但不知道如何读取配置属性做检查
• Spring Boot内部的OnPropertyCondition是非公开类，无法继承
• 尝试直接将@ConditionalOnProperty作为元注解并引用当前注解的value()属性，这种写法无效：

// INVALID CODE, DO NOT USE
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@ConditionalOnProperty(
    prefix = "myservice",
    name = "implversion",
    havingValue = OnMyServiceVersion.value()
)
public @interface OnMyServiceVersion {
    String value();
}

正确实现方案 #

步骤1：定义自定义注解

创建@OnMyServiceVersion注解，通过@Conditional指定自定义的条件判断类：

import org.springframework.context.annotation.Conditional;
import java.lang.annotation.*;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnMyServiceVersionCondition.class)
public @interface OnMyServiceVersion {
    String value();
}

步骤2：实现Condition判断类

编写OnMyServiceVersionCondition类，实现Condition接口，完成配置属性的读取与匹配逻辑：

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.core.env.Environment;
import java.util.Map;

public class OnMyServiceVersionCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // 获取自定义注解的属性值
        Map<String, Object> attributes = metadata.getAnnotationAttributes(OnMyServiceVersion.class.getName());
        if (attributes == null) {
            return false;
        }
        String targetVersion = (String) attributes.get("value");
        
        // 读取配置文件中的myservice.implversion配置
        Environment environment = context.getEnvironment();
        String currentVersion = environment.getProperty("myservice.implversion");
        
        // 对比版本值，匹配则允许Bean加载
        return targetVersion.equals(currentVersion);
    }
}

完成以上两步后，即可通过@OnMyServiceVersion(value = "a")替代原有的@ConditionalOnProperty配置，实现完全一致的Bean加载控制效果。

内容的提问来源于stack exchange，提问作者AdrienW