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    import ognl.OgnlContext;
018    import ognl.enhance.ExpressionAccessor;
019    
020    /**
021     * Wrapper around the OGNL library.
022     * 
023     * @author Howard M. Lewis Ship
024     * @since 4.0
025     */
026    public interface ExpressionEvaluator
027    {
028    
029        /**
030         * Reads a property of the target, defined by the expression.
031         * 
032         * @throws org.apache.hivemind.ApplicationRuntimeException
033         *             if the expression can not be parsed, or if some other error
034         *             occurs during evaluation of the expression.
035         */
036        Object read(Object target, String expression);
037    
038        /**
039         * Reads a property of the target, defined by the (previously compiled)
040         * expression.
041         * 
042         * @throws org.apache.hivemind.ApplicationRuntimeException
043         *             if some other error occurs during evaluation of the
044         *             expression.
045         */
046        Object readCompiled(Object target, Object expression);
047        
048        /**
049         * Reads a property of the target, defined by the (previously compiled)
050         * expression.
051         * 
052         * @param target
053         *          The object to resolve the expression against.
054         * @param expression
055         *          The compiled expression.
056         * @return
057         *          The result of reading on the expression.
058         */
059        Object read(Object target, ExpressionAccessor expression);
060        
061        /**
062         * Updates a property of the target, defined by the expression.
063         * 
064         * @throws org.apache.hivemind.ApplicationRuntimeException
065         *             if the expression can not be parsed, or if some other error
066         *             occurs during evaluation of the expression.
067         */
068        void write(Object target, String expression, Object value);
069    
070        /**
071         * Updates a property of the target, defined by the (previously compiled)
072         * expression.
073         * 
074         * @throws org.apache.hivemind.ApplicationRuntimeException
075         *             if some other error occurs during evaluation of the
076         *             expression.
077         */
078        void writeCompiled(Object target, Object expression, Object value);
079        
080        /**
081         * Updates a property of the target, defined by the (previously compiled)
082         * expression.
083         * 
084         * @param target
085         *          The target object to set a value on.
086         * @param expression
087         *          The pre-compiled expression.
088         * @param value
089         *          The value to set.
090         */
091        void write(Object target, ExpressionAccessor expression, Object value);
092        
093        /**
094         * Returns true if the expression evaluates to a constant or other literal
095         * value.
096         * 
097         * @throws org.apache.hivemind.ApplicationRuntimeException
098         *             if the expression is not valid
099         */
100        boolean isConstant(String expression);
101        
102        /**
103         * Returns true if the expression evaluates to a constant or other literal
104         * value.
105         * 
106         * @throws org.apache.hivemind.ApplicationRuntimeException
107         *             if the expression is not valid
108         */
109        boolean isConstant(Object target, String expression);
110        
111        /**
112         * Creates a default OGNL context object that can be used against
113         * the specified object for expression evaluation.
114         * 
115         * @param target 
116         *          The object to get a context for.
117         * @return 
118         *          An ognl context map.
119         */
120        OgnlContext createContext(Object target);
121    }