001    /*
002     * Copyright 2002-2004 the original author or authors.
003     * 
004     * Licensed under the Apache License, Version 2.0 (the "License"); you may not
005     * use this file except in compliance with the License. You may obtain a copy of
006     * the License at
007     * 
008     * http://www.apache.org/licenses/LICENSE-2.0
009     * 
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
012     * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
013     * License for the specific language governing permissions and limitations under
014     * the License.
015     */
016    package org.springframework.binding.value.support;
017    
018    import java.text.MessageFormat;
019    import java.util.Arrays;
020    import java.util.HashSet;
021    
022    import org.springframework.binding.value.ValueModel;
023    
024    /**
025     * A value model that takes a set of "argument" ValueModels, formats their 
026     * values into strings, and then inserts these formatted strings into the 
027     * provided pattern at the appropriate places. Any changes to the "argument" 
028     * ValueModels will cause this value model to also update.
029     *  
030     * @author Oliver Hutchison
031     * @see MessageFormat
032     */
033    public class MessageFormatValueModel extends AbstractDerivedValueModel {
034    
035        private final String pattern;
036    
037        private final ValueModel[] argumentValueModels;
038    
039        private String value;
040    
041        /**
042         * Constructs a new MessageFormatValueModel with a single argument.
043         * @param pattern the pattern 
044         * @param argumentValueModel the single value model holding the 
045         * value to be formatted and substituted
046         */
047        public MessageFormatValueModel(String pattern, ValueModel argumentValueModel) {
048            this(pattern, new ValueModel[] {argumentValueModel});
049        }
050    
051        /**
052         * Constructs a new MessageFormatValueModel with a group of arguments.
053         * @param pattern the pattern 
054         * @param argumentValueModels an array of value models holding the 
055         * value to be formatted and substituted
056         */
057        public MessageFormatValueModel(String pattern, ValueModel[] argumentValueModels) {
058            super((ValueModel[])new HashSet(Arrays.asList(argumentValueModels)).toArray(new ValueModel[0]));
059            this.pattern = pattern;
060            this.argumentValueModels = argumentValueModels;
061            // prime the initial value
062            sourceValuesChanged();
063        }
064        
065        protected void sourceValuesChanged() {
066            String oldValue = value;
067            value = MessageFormat.format(pattern, getArgumentValues());
068            fireValueChange(oldValue, value);        
069        }
070    
071        public Object getValue() {
072            return value;
073        }
074    
075        private Object[] getArgumentValues() {
076            Object[] values = new Object[argumentValueModels.length];
077            for (int i = 0; i < values.length; i++) {
078                values[i] = argumentValueModels[i].getValue();
079            }
080            return values;
081        }   
082    }