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.ref;
018    
019    import org.apache.camel.Exchange;
020    import org.apache.camel.Expression;
021    import org.apache.camel.IsSingleton;
022    import org.apache.camel.Predicate;
023    import org.apache.camel.builder.ExpressionBuilder;
024    import org.apache.camel.spi.Language;
025    import org.apache.camel.support.ExpressionAdapter;
026    import org.apache.camel.util.ExpressionToPredicateAdapter;
027    
028    /**
029     * A language for referred expressions.
030     */
031    public class RefLanguage implements Language, IsSingleton {
032    
033        public static Expression ref(Object value) {
034            String ref = value.toString();
035            return ExpressionBuilder.refExpression(ref);
036        }
037    
038        public Predicate createPredicate(String expression) {
039            return ExpressionToPredicateAdapter.toPredicate(createExpression(expression));
040        }
041    
042        public Expression createExpression(final String expression) {
043            final Expression exp = RefLanguage.ref(expression);
044            return new ExpressionAdapter() {
045                public Object evaluate(Exchange exchange) {
046                    Expression lookup = exp.evaluate(exchange, Expression.class);
047                    if (lookup != null) {
048                        return lookup.evaluate(exchange, Object.class);
049                    } else {
050                        throw new IllegalArgumentException("Cannot find expression in registry with ref: " + expression);
051                    }
052                }
053    
054                public String toString() {
055                    return exp.toString();
056                }
057            };
058        }
059    
060        public boolean isSingleton() {
061            return true;
062        }
063    }