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.builder;
018    
019    import org.apache.camel.BinaryPredicate;
020    import org.apache.camel.Exchange;
021    import org.apache.camel.Expression;
022    import org.apache.camel.Predicate;
023    
024    import static org.apache.camel.util.ObjectHelper.notNull;
025    
026    /**
027     * A useful base class for {@link Predicate} implementations
028     *
029     * @version 
030     */
031    public abstract class BinaryPredicateSupport implements BinaryPredicate {
032    
033        private final Expression left;
034        private final Expression right;
035    
036        protected BinaryPredicateSupport(Expression left, Expression right) {
037            notNull(left, "left");
038            notNull(right, "right");
039    
040            this.left = left;
041            this.right = right;
042        }
043    
044        @Override
045        public String toString() {
046            return left + " " + getOperationText() + " " + right;
047        }
048    
049        public boolean matches(Exchange exchange) {
050            return matchesReturningFailureMessage(exchange) == null;
051        }
052    
053        public String matchesReturningFailureMessage(Exchange exchange) {
054            // we must not store any state, so we can be thread safe
055            // and thus we offer this method which returns a failure message if
056            // we did not match
057            String answer = null;
058    
059            // must be thread safe and store result in local objects
060            Object leftValue = left.evaluate(exchange, Object.class);
061            Object rightValue = right.evaluate(exchange, Object.class);
062            if (!matches(exchange, leftValue, rightValue)) {
063                answer = leftValue + " " + getOperator() + " " + rightValue;
064            }
065    
066            return answer;
067        }
068    
069        protected abstract boolean matches(Exchange exchange, Object leftValue, Object rightValue);
070    
071        protected abstract String getOperationText();
072    
073        public Expression getLeft() {
074            return left;
075        }
076    
077        public Expression getRight() {
078            return right;
079        }
080    
081        public String getOperator() {
082            return getOperationText();
083        }
084    
085    }