/*
* 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.extension;
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。
* <p />
* 扩展点声明配置文件,格式修改。<br />
* 以Protocol示例,配置文件META-INF/dubbo/com.xxx.Protocol内容:<br />
* 由<br/>
* <pre><code>com.foo.XxxProtocol
com.foo.YyyProtocol</code></pre><br/>
* 改成使用KV格式<br/>
* <pre><code>xxx=com.foo.XxxProtocol
yyy=com.foo.YyyProtocol
* </code></pre>
* <br/>
* 原因:<br/>
* 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。
* <br/>
* 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。
*
* @author william.liangf
* @author ding.lid
* @export
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SPI {
/**
* 缺省扩展点名。
*/
String value() default "";
}