001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry.services;
016    
017    /**
018     * Wrapper around the OGNL library.
019     * 
020     * @author Howard M. Lewis Ship
021     * @since 4.0
022     */
023    public interface ExpressionEvaluator
024    {
025    
026        /**
027         * Reads a property of the target, defined by the expression.
028         * 
029         * @throws org.apache.hivemind.ApplicationRuntimeException
030         *             if the expression can not be parsed, or if some other error
031         *             occurs during evaluation of the expression.
032         */
033        Object read(Object target, String expression);
034    
035        /**
036         * Reads a property of the target, defined by the (previously compiled)
037         * expression.
038         * 
039         * @throws org.apache.hivemind.ApplicationRuntimeException
040         *             if some other error occurs during evaluation of the
041         *             expression.
042         */
043        Object readCompiled(Object target, Object expression);
044    
045        /**
046         * Updates a property of the target, defined by the expression.
047         * 
048         * @throws org.apache.hivemind.ApplicationRuntimeException
049         *             if the expression can not be parsed, or if some other error
050         *             occurs during evaluation of the expression.
051         */
052        void write(Object target, String expression, Object value);
053    
054        /**
055         * Updates a property of the target, defined by the (previously compiled)
056         * expression.
057         * 
058         * @throws org.apache.hivemind.ApplicationRuntimeException
059         *             if some other error occurs during evaluation of the
060         *             expression.
061         */
062        void writeCompiled(Object target, Object expression, Object value);
063    
064        /**
065         * Returns true if the expression evaluates to a constant or other literal
066         * value.
067         * 
068         * @throws org.apache.hivemind.ApplicationRuntimeException
069         *             if the expression is not valid
070         */
071        boolean isConstant(String expression);
072    }