001    // Copyright 2007, 2008, 2009, 2010 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.annotations;
016    
017    import static java.lang.annotation.RetentionPolicy.RUNTIME;
018    
019    import java.lang.annotation.Documented;
020    import java.lang.annotation.ElementType;
021    import java.lang.annotation.Retention;
022    import java.lang.annotation.Target;
023    
024    /**
025     * Marker annotation used to denote a service that is the primary instance of some common interface. This is often used
026     * when a service is a {@linkplain org.apache.tapestry5.ioc.services.ChainBuilder chain of command} or
027     * {@linkplain org.apache.tapestry5.ioc.services.StrategyBuilder strategy-based} and, therefore, many services will
028     * implement the
029     * same interface.
030     */
031    @Target(
032    { ElementType.PARAMETER, ElementType.FIELD, ElementType.METHOD })
033    @Retention(RUNTIME)
034    @Documented
035    @UseWith(AnnotationUseContext.SERVICE)
036    public @interface Primary
037    {
038    
039    }