1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.beanutils2.converters;
18
19 import java.lang.reflect.Array;
20 import java.util.Collection;
21 import java.util.Locale;
22 import java.util.Objects;
23
24 import org.apache.commons.beanutils2.ConversionException;
25 import org.apache.commons.beanutils2.ConvertUtils;
26 import org.apache.commons.beanutils2.Converter;
27 import org.apache.commons.logging.Log;
28 import org.apache.commons.logging.LogFactory;
29
30 /**
31 * Base {@link Converter} implementation that provides the structure for handling conversion <strong>to</strong> and <strong>from</strong> a specified type.
32 * <p>
33 * This implementation provides the basic structure for converting to/from a specified type optionally using a default value or throwing a
34 * {@link ConversionException} if a conversion error occurs.
35 * </p>
36 * <p>
37 * Implementations should provide conversion to the specified type and from the specified type to a {@code String} value by implementing the following methods:
38 * </p>
39 * <ul>
40 * <li>{@code convertToString(value)} - convert to a String (default implementation uses the objects {@code toString()} method).</li>
41 * <li>{@code convertToType(Class, value)} - convert to the specified type</li>
42 * </ul>
43 * <p>
44 * The default value has to be compliant to the default type of this converter - which is enforced by the generic type parameter. If a conversion is not
45 * possible and a default value is set, the converter tries to transform the default value to the requested target type. If this fails, a
46 * {@code ConversionException} if thrown.
47 * </p>
48 *
49 * @param <D> The default value type.
50 * @since 1.8.0
51 */
52 public abstract class AbstractConverter<D> implements Converter<D> {
53
54 /** Debug logging message to indicate default value configuration */
55 private static final String DEFAULT_CONFIG_MSG = "(N.B. Converters can be configured to use default values to avoid throwing exceptions)";
56
57 /** Current package name */
58 // getPackage() below returns null on some platforms/jvm versions during the unit tests.
59 // private static final String PACKAGE = AbstractConverter.class.getPackage().getName() + ".";
60 private static final String PACKAGE = "org.apache.commons.beanutils2.converters.";
61
62 /**
63 * Converts the given object to a lower-case string.
64 *
65 * @param value the input string.
66 * @return the given string trimmed and converter to lower-case.
67 */
68 protected static String toLowerCase(final Object value) {
69 return toString(value).toLowerCase(Locale.ROOT);
70 }
71
72 /**
73 * Converts the given object to a lower-case string.
74 *
75 * @param value the input string.
76 * @return the given string trimmed and converter to lower-case.
77 */
78 protected static String toString(final Object value) {
79 return Objects.requireNonNull(value, "value").toString();
80 }
81
82 /**
83 * Converts the given object to a lower-case string.
84 *
85 * @param value the input string.
86 * @return the given string trimmed and converter to lower-case.
87 */
88 protected static String toTrim(final Object value) {
89 return toString(value).trim();
90 }
91
92 /**
93 * Logging for this instance.
94 */
95 private transient Log log;
96
97 /**
98 * Should we return the default value on conversion errors?
99 */
100 private boolean useDefault;
101
102 /**
103 * The default value specified to our Constructor, if any.
104 */
105 private D defaultValue;
106
107 /**
108 * Constructs a <em>Converter</em> that throws a {@code ConversionException} if an error occurs.
109 */
110 public AbstractConverter() {
111 }
112
113 /**
114 * Constructs a <em>Converter</em> that returns a default value if an error occurs.
115 *
116 * @param defaultValue The default value to be returned if the value to be converted is missing or an error occurs converting the value.
117 */
118 public AbstractConverter(final D defaultValue) {
119 setDefaultValue(defaultValue);
120 }
121
122 /**
123 * Creates a standard conversion exception with a message indicating that the passed in value cannot be converted to the desired target type.
124 *
125 * @param type the target type
126 * @param value the value to be converted
127 * @return a {@code ConversionException} with a standard message
128 * @since 1.9
129 */
130 protected ConversionException conversionException(final Class<?> type, final Object value) {
131 return ConversionException.format("Can't convert value '%s' to type %s", value, type);
132 }
133
134 /**
135 * Converts the input object into an output object of the specified type.
136 *
137 * @param type Data type to which this value should be converted
138 * @param value The input value to be converted
139 * @return The converted value.
140 * @throws ConversionException if conversion cannot be performed successfully and no default is specified.
141 */
142 @Override
143 public <R> R convert(final Class<R> type, Object value) {
144 if (type == null) {
145 return convertToDefaultType(value);
146 }
147
148 Class<?> sourceType = value == null ? null : value.getClass();
149 final Class<R> targetType = ConvertUtils.primitiveToWrapper(type);
150
151 if (log().isDebugEnabled()) {
152 log().debug(
153 "Converting" + (value == null ? "" : " '" + toString(sourceType) + "'") + " value '" + value + "' to type '" + toString(targetType) + "'");
154 }
155
156 value = convertArray(value);
157
158 // Missing Value
159 if (value == null) {
160 return handleMissing(targetType);
161 }
162
163 sourceType = value.getClass();
164
165 try {
166 // Convert --> String
167 if (targetType.equals(String.class)) {
168 return targetType.cast(convertToString(value));
169
170 // No conversion necessary
171 }
172 if (targetType.equals(sourceType)) {
173 if (log().isDebugEnabled()) {
174 log().debug(" No conversion required, value is already a " + toString(targetType));
175 }
176 return targetType.cast(value);
177
178 // Convert --> Type
179 }
180 final Object result = convertToType(targetType, value);
181 if (log().isDebugEnabled()) {
182 log().debug(" Converted to " + toString(targetType) + " value '" + result + "'");
183 }
184 return targetType.cast(result);
185 } catch (final Throwable t) {
186 return handleError(targetType, value, t);
187 }
188 }
189
190 /**
191 * Returns the first element from an Array (or Collection) or the value unchanged if not an Array (or Collection).
192 *
193 * N.B. This needs to be overridden for array/Collection converters.
194 *
195 * @param value The value to convert
196 * @return The first element in an Array (or Collection) or the value unchanged if not an Array (or Collection)
197 */
198 protected Object convertArray(final Object value) {
199 if (value == null) {
200 return null;
201 }
202 if (value.getClass().isArray()) {
203 if (Array.getLength(value) > 0) {
204 return Array.get(value, 0);
205 }
206 return null;
207 }
208 if (value instanceof Collection) {
209 final Collection<?> collection = (Collection<?>) value;
210 if (!collection.isEmpty()) {
211 return collection.iterator().next();
212 }
213 return null;
214 }
215 return value;
216 }
217
218 /**
219 * Converts to the default type. This method is called if we do not have a target class. In this case, the T parameter is not set. Therefore, we can cast to
220 * it (which is required to fulfill the contract of the method signature).
221 *
222 * @param value the value to be converted
223 * @param <T> the type of the result object
224 * @return the converted value
225 */
226 @SuppressWarnings("unchecked")
227 private <T> T convertToDefaultType(final Object value) {
228 return (T) convert(getDefaultType(), value);
229 }
230
231 /**
232 * Converts the input object into a String.
233 * <p>
234 * <strong>N.B.</strong>This implementation simply uses the value's {@code toString()} method and should be overridden if a more sophisticated mechanism for
235 * <em>conversion to a String</em> is required.
236 * </p>
237 *
238 * @param value The input value to be converted.
239 * @return the converted String value.
240 * @throws IllegalArgumentException if an error occurs converting to a String
241 */
242 protected String convertToString(final Object value) {
243 return value.toString();
244 }
245
246 /**
247 * Converts the input object into an output object of the specified type.
248 * <p>
249 * Typical implementations will provide a minimum of {@code String --> type} conversion.
250 * </p>
251 *
252 * @param <R> Target type of the conversion.
253 * @param type Data type to which this value should be converted.
254 * @param value The input value to be converted.
255 * @return The converted value.
256 * @throws Throwable if an error occurs converting to the specified type
257 */
258 protected abstract <R> R convertToType(Class<R> type, Object value) throws Throwable;
259
260 /**
261 * Gets the default value for conversions to the specified type.
262 *
263 * @param type Data type to which this value should be converted.
264 * @return The default value for the specified type.
265 */
266 protected Object getDefault(final Class<?> type) {
267 if (type.equals(String.class)) {
268 return null;
269 }
270 return defaultValue;
271 }
272
273 /**
274 * Gets the default type this {@code Converter} handles.
275 *
276 * @return The default type this {@code Converter} handles.
277 */
278 protected abstract Class<D> getDefaultType();
279
280 /**
281 * Handles Conversion Errors.
282 * <p>
283 * If a default value has been specified then it is returned otherwise a ConversionException is thrown.
284 * </p>
285 *
286 * @param <T> Target type of the conversion.
287 * @param type Data type to which this value should be converted.
288 * @param value The input value to be converted
289 * @param cause The exception thrown by the {@code convert} method
290 * @return The default value.
291 * @throws ConversionException if no default value has been specified for this {@link Converter}.
292 */
293 protected <T> T handleError(final Class<T> type, final Object value, final Throwable cause) {
294 if (log().isDebugEnabled()) {
295 if (cause instanceof ConversionException) {
296 log().debug(" Conversion threw ConversionException: " + cause.getMessage());
297 } else {
298 log().debug(" Conversion threw " + cause);
299 }
300 }
301 if (useDefault) {
302 return handleMissing(type);
303 }
304 ConversionException cex = null;
305 if (cause instanceof ConversionException) {
306 cex = (ConversionException) cause;
307 if (log().isDebugEnabled()) {
308 log().debug(" Re-throwing ConversionException: " + cex.getMessage());
309 log().debug(" " + DEFAULT_CONFIG_MSG);
310 }
311 } else {
312 final String msg = "Error converting from '" + toString(value.getClass()) + "' to '" + toString(type) + "' " + cause.getMessage();
313 cex = new ConversionException(msg, cause);
314 if (log().isDebugEnabled()) {
315 log().debug(" Throwing ConversionException: " + msg);
316 log().debug(" " + DEFAULT_CONFIG_MSG);
317 }
318 }
319 throw cex;
320 }
321
322 /**
323 * Handles missing values.
324 * <p>
325 * If a default value has been specified, then it is returned (after a cast to the desired target class); otherwise a ConversionException is thrown.
326 * </p>
327 *
328 * @param <T> the desired target type
329 * @param type Data type to which this value should be converted.
330 * @return The default value.
331 * @throws ConversionException if no default value has been specified for this {@link Converter}.
332 */
333 protected <T> T handleMissing(final Class<T> type) {
334 if (useDefault || type.equals(String.class)) {
335 Object value = getDefault(type);
336 if (useDefault && value != null && !type.equals(value.getClass())) {
337 try {
338 value = convertToType(type, defaultValue);
339 } catch (final Throwable t) {
340 throw new ConversionException("Default conversion to " + toString(type) + " failed.", t);
341 }
342 }
343 if (log().isDebugEnabled()) {
344 log().debug(" Using default " + (value == null ? "" : toString(value.getClass()) + " ") + "value '" + defaultValue + "'");
345 }
346 // value is now either null or of the desired target type
347 return type.cast(value);
348 }
349
350 final ConversionException cex = ConversionException.format("No value specified for '%s'", toString(type));
351 if (log().isDebugEnabled()) {
352 log().debug(" Throwing ConversionException: " + cex.getMessage());
353 log().debug(" " + DEFAULT_CONFIG_MSG);
354 }
355 throw cex;
356 }
357
358 /**
359 * Tests whether a default value will be returned or exception thrown in the event of a conversion error.
360 *
361 * @return {@code true} if a default value will be returned for conversion errors or {@code false} if a {@link ConversionException} will be thrown.
362 */
363 public boolean isUseDefault() {
364 return useDefault;
365 }
366
367 /**
368 * Gets the Log instance.
369 * <p>
370 * The Log instance variable is transient and accessing it through this method ensures it is re-initialized when this instance is de-serialized.
371 * </p>
372 *
373 * @return The Log instance.
374 */
375 Log log() {
376 if (log == null) {
377 log = LogFactory.getLog(getClass());
378 }
379 return log;
380 }
381
382 /**
383 * Sets the default value, converting as required.
384 * <p>
385 * If the default value is different from the type the {@code Converter} handles, it will be converted to the handled type.
386 * </p>
387 *
388 * @param defaultValue The default value to be returned if the value to be converted is missing or an error occurs converting the value.
389 * @throws ConversionException if an error occurs converting the default value
390 */
391 protected void setDefaultValue(final D defaultValue) {
392 useDefault = false;
393 if (log().isDebugEnabled()) {
394 log().debug("Setting default value: " + defaultValue);
395 }
396 if (defaultValue == null) {
397 this.defaultValue = null;
398 } else {
399 this.defaultValue = convert(getDefaultType(), defaultValue);
400 }
401 useDefault = true;
402 }
403
404 /**
405 * Converts this instance to a String.
406 *
407 * @return A String representation of this converter
408 */
409 @Override
410 public String toString() {
411 return toString(getClass()) + "[UseDefault=" + useDefault + "]";
412 }
413
414 /**
415 * Converts a {@link Class} to a String.
416 *
417 * @param type The {@link Class}.
418 * @return The String representation.
419 */
420 String toString(final Class<?> type) {
421 String typeName = null;
422 if (type == null) {
423 typeName = "null";
424 } else if (type.isArray()) {
425 Class<?> elementType = type.getComponentType();
426 int count = 1;
427 while (elementType.isArray()) {
428 elementType = elementType.getComponentType();
429 count++;
430 }
431 final StringBuilder typeNameBuilder = new StringBuilder(elementType.getName());
432 for (int i = 0; i < count; i++) {
433 typeNameBuilder.append("[]");
434 }
435 typeName = typeNameBuilder.toString();
436 } else {
437 typeName = type.getName();
438 }
439 if (typeName.startsWith("java.lang.") || typeName.startsWith("java.util.") || typeName.startsWith("java.math.")) {
440 typeName = typeName.substring("java.lang.".length());
441 } else if (typeName.startsWith(PACKAGE)) {
442 typeName = typeName.substring(PACKAGE.length());
443 }
444 return typeName;
445 }
446
447 }