@Retention(RUNTIME)
@Target(TYPE)
public @interface MetadataDefinition

用于定义新类型的事件元数据的元注释。

在以下示例中，使用两个用户定义的注释@Severity和@TransactionId定义事务事件。

   @MetadataDefinition @Label("Severity") @Description("Value between 0 and 100 that indicates severity. 100 is most severe.") @Retention(RetentionPolicy.RUNTIME) @Target({ ElementType.TYPE }) public @interface @Severity { int value() default 50; } @MetadataDefinition @Label("Transaction Id") @Relational @Retention(RetentionPolicy.RUNTIME) @Target({ ElementType.FIELD }) public @interface @Severity { } @Severity(80) @Label("Transaction Blocked"); class TransactionBlocked extends Event { @TransactionId @Label("Transaction"); long transactionId; @TransactionId @Label("Transaction Blocker"); long transactionId; }  

将@MetadataDefinition添加到@Severity和@TransactionId的声明中可确保Flight Recorder保存信息。