
org.apache.dubbo.common.extension.Adaptive Maven / Gradle / Ivy
/*
* 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.dubbo.common.extension;
import org.apache.dubbo.common.URL;
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;
/**
* Provide helpful information for {@link ExtensionLoader} to inject dependency extension instance.
*
* @see ExtensionLoader
* @see URL
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface Adaptive {
/**
* Decide which target extension to be injected. The name of the target extension is decided by the parameter passed
* in the URL, and the parameter names are given by this method.
*
* If the specified parameters are not found from {@link URL}, then the default extension will be used for
* dependency injection (specified in its interface's {@link SPI}).
*
* For example, given String[] {"key1", "key2"}
:
*
* - find parameter 'key1' in URL, use its value as the extension's name
* - try 'key2' for extension's name if 'key1' is not found (or its value is empty) in URL
* - use default extension if 'key2' doesn't exist either
* - otherwise, throw {@link IllegalStateException}
*
* If the parameter names are empty, then a default parameter name is generated from interface's
* class name with the rule: divide classname from capital char into several parts, and separate the parts with
* dot '.', for example, for {@code org.apache.dubbo.xxx.YyyInvokerWrapper}, the generated name is
* String[] {"yyy.invoker.wrapper"}
.
*
* @return parameter names in URL
*/
String[] value() default {};
}
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