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         * Reads a property of the target, defined by the expression.
027         * 
028         * @throws org.apache.hivemind.ApplicationRuntimeException
029         *             if the expression can not be parsed, or if some other error occurs during
030         *             evaluation of the expression.
031         */
032        public Object read(Object target, String expression);
033    
034        /**
035         * Reads a property of the target, defined by the (previously compiled) expression.
036         * 
037         * @throws org.apache.hivemind.ApplicationRuntimeException
038         *             if some other error occurs during evaluation of the expression.
039         */
040        public Object readCompiled(Object target, Object expression);
041    
042        /**
043         * Updates a property of the target, defined by the expression.
044         * 
045         * @throws org.apache.hivemind.ApplicationRuntimeException
046         *             if the expression can not be parsed, or if some other error occurs during
047         *             evaluation of the expression.
048         */
049        public void write(Object target, String expression, Object value);
050    
051        /**
052         * Updates a property of the target, defined by the (previously compiled) expression.
053         * 
054         * @throws org.apache.hivemind.ApplicationRuntimeException
055         *             if some other error occurs during evaluation of the expression.
056         */
057        public void writeCompiled(Object target, Object expression, Object value);
058    
059        /**
060         * Returns true if the expression evaluates to a constant or other literal value.
061         * 
062         * @throws org.apache.hivemind.ApplicationRuntimeException
063         *             if the expression is not valid
064         */
065        public boolean isConstant(String expression);
066    }