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    /**
020     * A predicate which is evaluating a binary expression.
021     * <p/>
022     * The predicate has a left and right hand side expressions which
023     * is matched based on an operator.
024     * <p/>
025     * This predicate offers the {@link #matchesReturningFailureMessage} method
026     * which evaluates and return a detailed failure message if the predicate did not match.
027     *
028     * @version 
029     */
030    public interface BinaryPredicate extends Predicate {
031    
032        /**
033         * Gets the operator
034         *
035         * @return the operator text
036         */
037        String getOperator();
038    
039        /**
040         * Gets the left hand side expression
041         *
042         * @return the left expression
043         */
044        Expression getLeft();
045    
046        /**
047         * Gets the right hand side expression
048         *
049         * @return the right expression
050         */
051        Expression getRight();
052    
053        /**
054         * Evaluates the predicate on the message exchange and returns <tt>null</tt> if this
055         * exchange matches the predicate. If it did <b>not</b> match, then a failure message
056         * is returned detailing why it did not fail, which can be used for end users to understand
057         * the failure.
058         *
059         * @param exchange the message exchange
060         * @return <tt>null</tt> if the predicate matches.
061         */
062        String matchesReturningFailureMessage(Exchange exchange);
063    
064    }