com.alibaba.dubbo.common.Extension Maven / Gradle / Ivy

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/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed 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 com.alibaba.dubbo.common;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 扩展点接口的标识。
 * 
 * 扩展点声明配置文件，格式修改。

 * 以Protocol示例，配置文件META-INF/dubbo/com.xxx.Protocol内容：

 * 由

 * 
com.foo.XxxProtocol
 com.foo.YyyProtocol


 * 改成使用KV格式

 * xxx=com.foo.XxxProtocol
 yyy=com.foo.YyyProtocol
 * 
 * 

 * 原因：

 * 当扩展点的static字段或方法签名上引用了三方库，
 * 如果三方库不存在，会导致类初始化失败，
 * Extension标识Dubbo就拿不到了，异常信息就和配置对应不起来。
 * 

 * 比如:
 * Extension("mina")加载失败，
 * 当用户配置使用mina时，就会报找不到扩展点，
 * 而不是报加载扩展点失败，以及失败原因。
 * 
 * @deprecated 因为含义广泛废弃，改用功 {@link com.alibaba.dubbo.common.extension.SPI}
 * @author william.liangf
 * @author ding.lid
 * @export
 */
@Deprecated
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface Extension {

    /**
     * @deprecated
     */
    @Deprecated
	String value() default "";

}