我可以将@ConditionalProperty与我的自定义注释一起使用，以避免重复配置吗？

Question

我想使用@OnConditional*家族注释将我的Spring Boot App的代码逻辑地划分为几个“特性”。

我发现自己重复了很多代码，比如：

@ConditionalOnProperty( prefix = "pib2.war.features.", value = "hello", matchIfMissing = false )
@RestController
public class HelloController {
...
}

为了简化维护，我想定义元注释，这样我就可以创建某种“功能切换”，比如：

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@ConditionalOnProperty( prefix = "pib2.war.features" )
public @interface FeatureToggle {

    @AliasFor(annotation = ConditionalOnProperty.class )
    String[] value() default { };

    @AliasFor(annotation = ConditionalOnProperty.class )
    String[] name() default { };
}

这样我的代码就变成了：

@FeatureToggle( "hello" )
@RestController
public class HelloController {
...
}

但这似乎不起作用：OnPropertyCondition求值代码忽略了by @Aliased字段，它只是说名称为空：

...
Caused by: java.lang.IllegalStateException: The name or value attribute of @ConditionalOnProperty must be specified
    at org.springframework.util.Assert.state(Assert.java:73)
    at org.springframework.boot.autoconfigure.condition.OnPropertyCondition$Spec.getNames(OnPropertyCondition.java:129)
    at org.springframework.boot.autoconfigure.condition.OnPropertyCondition$Spec.<init>(OnPropertyCondition.java:122)
    at org.springframework.boot.autoconfigure.condition.OnPropertyCondition.determineOutcome(OnPropertyCondition.java:88)
    at org.springframework.boot.autoconfigure.condition.OnPropertyCondition.getMatchOutcome(OnPropertyCondition.java:55)
    at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47)
    ... 90 common frames omitted

所以我猜创建这些快捷的元注注是不可能的？我的配置是不是错了？我是否应该像“OnPropertyCondition`”那样编写自己的条件求值器？

Answer 1

如果您想编写自己的条件，则应该实现org.springframework.context.annotation.Condition

这是通过定义一个实现Condition接口的ProfileCondition类来实现@Profile的工作方式：

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(ProfileCondition.class)
public @interface Profile {

    /**
     * The set of profiles for which the annotated component should be registered.
     */
    String[] value();

}