001 /*
002 * Copyright 2004 The Apache Software Foundation
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of 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,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016 package org.apache.commons.convert.conversion;
017
018 import org.apache.commons.convert.Conversion;
019 import org.apache.commons.convert.Converter;
020
021 /**
022 * Abstract base class for conversion objects that provides basic features.
023 * <p>
024 * Most Conversion implementations will extend this class. It provides convenient
025 * implementations of the methods of the interface, and simplifies null-handling
026 * in the subclass.
027 * <p>
028 * To implement a conversion from a single class, simply extend this class and
029 * implement the {@link #convertValue(Object, Converter)} method. To implement a
030 * conversion from a class and its subclasses, use {@link AbstractConversionFactory}.
031 *
032 * @author Stephen Colebourne
033 * @version $Id: AbstractConversion.java 155441 2005-02-26 13:19:22Z dirkv $
034 * @since 1.0
035 */
036 public abstract class AbstractConversion implements Conversion {
037
038 /** Useful constant for subclass constructors */
039 protected static final Class STRING_CLASS = String.class;
040
041 /** The type to convert from */
042 private final Class fromType;
043 /** The type to convert to */
044 private final Class toType;
045
046 /**
047 * Constructor that stores the from and to types.
048 *
049 * @param fromType the type to convert from
050 * @param toType the type to convert to
051 */
052 protected AbstractConversion(Class fromType, Class toType) {
053 super();
054 this.fromType = fromType;
055 this.toType = toType;
056 }
057
058 //-----------------------------------------------------------------------
059 /**
060 * Converts an object from one type to another.
061 * <p>
062 * This implementation delegates to <code>convertValue</code> after handling null.
063 * If the null-safe behaviour is undesired, override this method.
064 *
065 * @param value the input value to be converted, may be null
066 * @param converter the converter being used, not null
067 * @return the converted value
068 * @throws Exception if conversion fails, use ConversionException if creating
069 * a new exception, otherwise just allow exceptions to be thrown
070 */
071 public Object convert(Object value, Converter converter) throws Exception {
072 if (value == null) {
073 return null;
074 }
075 return convertValue(value, converter);
076 }
077
078 /**
079 * Convert the specified non-null value to another type.
080 *
081 * @param value the input value to be converted, pre-checked to not be null
082 * @param converter the converter being used, not null
083 * @return the converted value
084 * @throws Exception if conversion fails, use ConversionException if creating
085 * a new exception, otherwise just allow exceptions to be thrown
086 */
087 protected Object convertValue(Object value, Converter converter) throws Exception {
088 throw new UnsupportedOperationException("Not implemented");
089 }
090
091 //-----------------------------------------------------------------------
092 /**
093 * The type to convert from.
094 *
095 * @return the Class object representing the class to convert to
096 */
097 public Class getFromType() {
098 return fromType;
099 }
100
101 /**
102 * The type to convert to.
103 *
104 * @return the Class object representing the class to convert from
105 */
106 public Class getToType() {
107 return toType;
108 }
109
110 //-----------------------------------------------------------------------
111 /**
112 * Gets a suitable debugging string.
113 *
114 * @return a debugging string
115 */
116 public String toString() {
117 String from = convertClassToName(getFromType());
118 String to = convertClassToName(getToType());
119 return "Conversion[" + from + "->" + to + "]";
120 }
121
122 /**
123 * Converts a class to a string name for debugging.
124 *
125 * @param cls the class to convert
126 * @return the class name
127 */
128 private String convertClassToName(Class cls) {
129 if (cls == null) {
130 return "null";
131 }
132 String str = cls.getName();
133 int pos = str.lastIndexOf('.');
134 if (str.substring(0, pos).equals("java.lang")) {
135 str = str.substring(pos + 1);
136 }
137 if (str.substring(0, pos).equals("java.util")) {
138 str = str.substring(pos + 1);
139 }
140 return str;
141 }
142
143 }