1 /*
2 * Copyright 2004 The Apache Software Foundation
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package org.apache.commons.convert.conversion;
17
18 import org.apache.commons.convert.Conversion;
19 import org.apache.commons.convert.Converter;
20
21 /**
22 * Abstract base class for conversion objects that provides basic features.
23 * <p>
24 * Most Conversion implementations will extend this class. It provides convenient
25 * implementations of the methods of the interface, and simplifies null-handling
26 * in the subclass.
27 * <p>
28 * To implement a conversion from a single class, simply extend this class and
29 * implement the {@link #convertValue(Object, Converter)} method. To implement a
30 * conversion from a class and its subclasses, use {@link AbstractConversionFactory}.
31 *
32 * @author Stephen Colebourne
33 * @version $Id: AbstractConversion.java 155441 2005-02-26 13:19:22Z dirkv $
34 * @since 1.0
35 */
36 public abstract class AbstractConversion implements Conversion {
37
38 /** Useful constant for subclass constructors */
39 protected static final Class STRING_CLASS = String.class;
40
41 /** The type to convert from */
42 private final Class fromType;
43 /** The type to convert to */
44 private final Class toType;
45
46 /**
47 * Constructor that stores the from and to types.
48 *
49 * @param fromType the type to convert from
50 * @param toType the type to convert to
51 */
52 protected AbstractConversion(Class fromType, Class toType) {
53 super();
54 this.fromType = fromType;
55 this.toType = toType;
56 }
57
58 //-----------------------------------------------------------------------
59 /**
60 * Converts an object from one type to another.
61 * <p>
62 * This implementation delegates to <code>convertValue</code> after handling null.
63 * If the null-safe behaviour is undesired, override this method.
64 *
65 * @param value the input value to be converted, may be null
66 * @param converter the converter being used, not null
67 * @return the converted value
68 * @throws Exception if conversion fails, use ConversionException if creating
69 * a new exception, otherwise just allow exceptions to be thrown
70 */
71 public Object convert(Object value, Converter converter) throws Exception {
72 if (value == null) {
73 return null;
74 }
75 return convertValue(value, converter);
76 }
77
78 /**
79 * Convert the specified non-null value to another type.
80 *
81 * @param value the input value to be converted, pre-checked to not be null
82 * @param converter the converter being used, not null
83 * @return the converted value
84 * @throws Exception if conversion fails, use ConversionException if creating
85 * a new exception, otherwise just allow exceptions to be thrown
86 */
87 protected Object convertValue(Object value, Converter converter) throws Exception {
88 throw new UnsupportedOperationException("Not implemented");
89 }
90
91 //-----------------------------------------------------------------------
92 /**
93 * The type to convert from.
94 *
95 * @return the Class object representing the class to convert to
96 */
97 public Class getFromType() {
98 return fromType;
99 }
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 }