RefLanguage.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.camel.language.ref;

import org.apache.camel.Exchange;
import org.apache.camel.Expression;
import org.apache.camel.IsSingleton;
import org.apache.camel.Predicate;
import org.apache.camel.builder.ExpressionBuilder;
import org.apache.camel.spi.Language;
import org.apache.camel.support.ExpressionAdapter;
import org.apache.camel.util.ExpressionToPredicateAdapter;
import org.apache.camel.util.PredicateToExpressionAdapter;

/**
 * A language for referred expressions or predicates.
 */
public class RefLanguage implements Language, IsSingleton {

    public static Expression ref(Object value) {
        String ref = value.toString();
        return ExpressionBuilder.refExpression(ref);
    }

    public Predicate createPredicate(String expression) {
        return ExpressionToPredicateAdapter.toPredicate(createExpression(expression));
    }

    public Expression createExpression(final String expression) {
        final Expression exp = RefLanguage.ref(expression);
        return new ExpressionAdapter() {
            public Object evaluate(Exchange exchange) {
                Expression target = null;

                Object lookup = exp.evaluate(exchange, Object.class);

                // must favor expression over predicate
                if (lookup != null && lookup instanceof Expression) {
                    target = (Expression) lookup;
                } else if (lookup != null && lookup instanceof Predicate) {
                    target = PredicateToExpressionAdapter.toExpression((Predicate) lookup);
                }

                if (target != null) {
                    return target.evaluate(exchange, Object.class);
                } else {
                    throw new IllegalArgumentException("Cannot find expression or predicate in registry with ref: " + expression);
                }
            }

            public String toString() {
                return exp.toString();
            }
        };
    }

    public boolean isSingleton() {
        return true;
    }
}