001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.camel;
018    
019    import java.lang.annotation.Documented;
020    import java.lang.annotation.ElementType;
021    import java.lang.annotation.Retention;
022    import java.lang.annotation.RetentionPolicy;
023    import java.lang.annotation.Target;
024    
025    /**
026     * An annotation used to mark methods to indicate code capable of being a
027     * fallback converter which are then auto-discovered using
028     * the <a href="http://camel.apache.org/type-converter.html">Type
029     * Conversion Support</a>.
030     * <p/>
031     * The difference between a regular <tt>@Converter</tt> and a <tt>@FallbackConverter</tt>
032     * is that the fallback is resolved at last if no regular converter could be found.
033     * Also the method signature is scoped to be generic to allow handling a broader range
034     * of types trying to be converted. The fallback converter can just return <tt>null</tt>
035     * if it can not handle the types to convert from/to.
036     *
037     * @see org.apache.camel.component.file.GenericFileConverter GenericFileConverter for an example.
038     *
039     * @version 
040     */
041    @Retention(RetentionPolicy.RUNTIME)
042    @Documented
043    @Target({ElementType.TYPE, ElementType.METHOD })
044    public @interface FallbackConverter {
045    
046        /**
047         * Whether or not returning <tt>null</tt> is a valid response.
048         */
049        boolean allowNull() default false;
050    
051        /**
052         * Whether or not this fallback converter can be promoted to a first class type converter.
053         */
054        boolean canPromote() default false;
055    
056    }