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.language.header;
018    
019    import org.apache.camel.Expression;
020    import org.apache.camel.IsSingleton;
021    import org.apache.camel.Predicate;
022    import org.apache.camel.builder.ExpressionBuilder;
023    import org.apache.camel.spi.Language;
024    import org.apache.camel.util.ExpressionToPredicateAdapter;
025    
026    /**
027     * A language for header expressions.
028     */
029    public class HeaderLanguage implements Language, IsSingleton {
030    
031        public static Expression header(String headerName) {        
032            return ExpressionBuilder.headerExpression(headerName);
033        }
034    
035        public Predicate createPredicate(String expression) {
036            return ExpressionToPredicateAdapter.toPredicate(createExpression(expression));
037        }
038    
039        public Expression createExpression(String expression) {
040            return HeaderLanguage.header(expression);
041        }
042    
043        public boolean isSingleton() {
044            return true;
045        }
046    }