1 /*
   2  * Copyright (c) 2016, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.jfr;
  27 
  28 import java.lang.annotation.ElementType;
  29 import java.lang.annotation.Retention;
  30 import java.lang.annotation.RetentionPolicy;
  31 import java.lang.annotation.Target;
  32 
  33 /**
  34  * Meta annotation for defining new types of event metadata.
  35  * <p>
  36  * In the following example, a transaction event is defined with two
  37  * user-defined annotations, {@code @Severity} and {@code @TransactionId}.
  38  *
  39  * <pre>
  40  * <code>
  41  *{@literal @}MetadataDefinition
  42  *{@literal @}Label("Severity")
  43  *{@literal @}Description("Value between 0 and 100 that indicates severity. 100 is most severe.")
  44  *{@literal @}Retention(RetentionPolicy.RUNTIME)
  45  *{@literal @}Target({ ElementType.TYPE })
  46  * public {@literal @}interface {@literal @}Severity {
  47  *   int value() default 50;
  48  * }
  49  *
  50  *{@literal @}MetadataDefinition
  51  *{@literal @}Label("Transaction Id")
  52  *{@literal @}Relational
  53  *{@literal @}Retention(RetentionPolicy.RUNTIME)
  54  *{@literal @}Target({ ElementType.FIELD })
  55  * public {@literal @}interface {@literal @}Severity {
  56  * }
  57  *
  58  *{@literal @}Severity(80)
  59  *{@literal @}Label("Transaction Blocked");
  60  * class TransactionBlocked extends Event {
  61  *  {@literal @}TransactionId
  62  *  {@literal @}Label("Transaction");
  63  *   long transactionId;
  64  *
  65  *  {@literal @}TransactionId
  66  *  {@literal @}Label("Transaction Blocker");
  67  *   long transactionId;
  68  * }
  69  *
  70  * </code>
  71  * </pre>
  72  *
  73  * Adding {@code @MetadataDefinition} to the declaration of {@code @Severity} and {@code @TransactionId}
  74  * ensures the information is saved by Flight Recorder.
  75  *
  76  * @since 8
  77  */
  78 @Retention(RetentionPolicy.RUNTIME)
  79 @Target({ ElementType.TYPE })
  80 public @interface MetadataDefinition {
  81 }