Hadoop註解InterfaceAudience InterfaceStability
Hadoop註解InterfaceAudience InterfaceStability
最近學習Hadoop時,看到InputFormat上面兩個註解,是以前沒有見過的,做一個簡單記錄
@InterfaceAudience.Public
@InterfaceStability.Stable
1. InterfaceAudience
InterfaceAudience源碼
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.classification;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
/**
* Annotation to inform users of a package, class or method's intended audience.
* Currently the audience can be {@link Public}, {@link LimitedPrivate} or
* {@link Private}. <br>
* All public classes must have InterfaceAudience annotation. <br>
* <ul>
* <li>Public classes that are not marked with this annotation must be
* considered by default as {@link Private}.</li>
*
* <li>External applications must only use classes that are marked
* {@link Public}. Avoid using non public classes as these classes
* could be removed or change in incompatible ways.</li>
*
* <li>Hadoop projects must only use classes that are marked
* {@link LimitedPrivate} or {@link Public}</li>
*
* <li> Methods may have a different annotation that it is more restrictive
* compared to the audience classification of the class. Example: A class
* might be {@link Public}, but a method may be {@link LimitedPrivate}
* </li></ul>
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class InterfaceAudience {
/**
* Intended for use by any project or application.
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Public {};
/**
* Intended only for the project(s) specified in the annotation.
* For example, "Common", "HDFS", "MapReduce", "ZooKeeper", "HBase".
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface LimitedPrivate {
String[] value();
};
/**
* Intended for use only within Hadoop itself.
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Private {};
private InterfaceAudience() {} // Audience can't exist on its own
}
從源碼中可以看出,InterfaceAudience有3個類型,用來說明被註解的類使用的作用範圍
Public:可以給任何項目和應用程序使用
LimitedPrivate:僅僅可以使用在“Common”、“HDFS”、“MapReduce”、“ZooKeeper”、“HBase”
Private:僅僅可以在Hadoop本身內使用
2. InterfaceStability
InterfaceStability源碼
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.classification;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import org.apache.hadoop.classification.InterfaceAudience.LimitedPrivate;
import org.apache.hadoop.classification.InterfaceAudience.Private;
import org.apache.hadoop.classification.InterfaceAudience.Public;
/**
* Annotation to inform users of how much to rely on a particular package,
* class or method not changing over time. Currently the stability can be
* {@link Stable}, {@link Evolving} or {@link Unstable}. <br>
*
* <ul><li>All classes that are annotated with {@link Public} or
* {@link LimitedPrivate} must have InterfaceStability annotation. </li>
* <li>Classes that are {@link Private} are to be considered unstable unless
* a different InterfaceStability annotation states otherwise.</li>
* <li>Incompatible changes must not be made to classes marked as stable.</li>
* </ul>
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class InterfaceStability {
/**
* Can evolve while retaining compatibility for minor release boundaries.;
* can break compatibility only at major release (ie. at m.0).
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Stable {};
/**
* Evolving, but can break compatibility at minor release (i.e. m.x)
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Evolving {};
/**
* No guarantee is provided as to reliability or stability across any
* level of release granularity.
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Unstable {};
}
從源碼可以看出,InterfaceStability有3個類型,用來說明被註解的類的穩定性
Stable:說明主版本是穩定的,不同主版本之間可能不兼容
Evolving:說明在不停的變化,不同小版本之間也可能不兼容
UnStable:無法保證其可靠性和穩定性