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 */
017package org.apache.camel;
018
019import java.lang.annotation.Documented;
020import java.lang.annotation.ElementType;
021import java.lang.annotation.Retention;
022import java.lang.annotation.RetentionPolicy;
023import 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 })
044public @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}