component.java

一套java版本的搜索引擎源码

/**
 * 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.lucene.gdata.server.registry;

import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * The {@link Component} annotation is used to annotate a class as a
 * server-component of the GDATA-Server. Annotated class can be configured via
 * the gdata-config.xml file to be looked up by aribaty classes at runtime via
 * the
 * {@link org.apache.lucene.gdata.server.registry.GDataServerRegistry#lookup(Class, ComponentType)}
 * method.
 * <p>
 * Classes annotated with the Component annotation need to provide a default
 * constructor to be instanciated via reflection. Components of the GData-Server
 * are definded in the
 * {@link org.apache.lucene.gdata.server.registry.ComponentType} enumeration.
 * Each of the enum types are annotated with a
 * {@link org.apache.lucene.gdata.server.registry.SuperType} annotation. This
 * annotation specifies the super class or interface of the component. A class
 * annotated with the Component annotation must implement or extends this
 * defined super-type. This enables developers to use custom implemetations of
 * the component like a custom {@link org.apache.lucene.gdata.storage.Storage}.
 * </p>
 * <p>
 * Each ComponentType can only registerd once as the
 * {@link org.apache.lucene.gdata.server.registry.GDataServerRegistry} does not
 * provide multipe instances of a ComponentType.
 * </p>
 * <p>
 * This annotation can only annotate types and can be accessed at runtime.
 * {@link java.lang.annotation.Target} ==
 * {@link java.lang.annotation.ElementType#TYPE} and
 * {@link java.lang.annotation.Retention} ==
 * {@link java.lang.annotation.RetentionPolicy#RUNTIME}.
 * 
 * @see org.apache.lucene.gdata.server.registry.GDataServerRegistry
 * @see org.apache.lucene.gdata.server.registry.ComponentType
 * @see org.apache.lucene.gdata.server.registry.SuperType
 * 
 * 
 * @author Simon Willnauer
 * 
 */
@Target( { TYPE })
@Retention(value = RUNTIME)
public @interface Component {

    /**
     * @see ComponentType
     * @return - the component type
     */
    ComponentType componentType();

}