001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.beanutils2.converters;
018
019import java.lang.reflect.Array;
020import java.util.Collection;
021import java.util.Locale;
022import java.util.Objects;
023
024import org.apache.commons.beanutils2.ConversionException;
025import org.apache.commons.beanutils2.ConvertUtils;
026import org.apache.commons.beanutils2.Converter;
027import org.apache.commons.logging.Log;
028import org.apache.commons.logging.LogFactory;
029
030/**
031 * Base {@link Converter} implementation that provides the structure for handling conversion <strong>to</strong> and <strong>from</strong> a specified type.
032 * <p>
033 * This implementation provides the basic structure for converting to/from a specified type optionally using a default value or throwing a
034 * {@link ConversionException} if a conversion error occurs.
035 * </p>
036 * <p>
037 * Implementations should provide conversion to the specified type and from the specified type to a {@code String} value by implementing the following methods:
038 * </p>
039 * <ul>
040 * <li>{@code convertToString(value)} - convert to a String (default implementation uses the objects {@code toString()} method).</li>
041 * <li>{@code convertToType(Class, value)} - convert to the specified type</li>
042 * </ul>
043 * <p>
044 * 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
045 * possible and a default value is set, the converter tries to transform the default value to the requested target type. If this fails, a
046 * {@code ConversionException} if thrown.
047 * </p>
048 *
049 * @param <D> The default value type.
050 * @since 1.8.0
051 */
052public abstract class AbstractConverter<D> implements Converter<D> {
053
054    /** Debug logging message to indicate default value configuration */
055    private static final String DEFAULT_CONFIG_MSG = "(N.B. Converters can be configured to use default values to avoid throwing exceptions)";
056
057    /** Current package name */
058    // getPackage() below returns null on some platforms/jvm versions during the unit tests.
059    // private static final String PACKAGE = AbstractConverter.class.getPackage().getName() + ".";
060    private static final String PACKAGE = "org.apache.commons.beanutils2.converters.";
061
062    /**
063     * Converts the given object to a lower-case string.
064     *
065     * @param value the input string.
066     * @return the given string trimmed and converter to lower-case.
067     */
068    protected static String toLowerCase(final Object value) {
069        return toString(value).toLowerCase(Locale.ROOT);
070    }
071
072    /**
073     * Converts the given object to a lower-case string.
074     *
075     * @param value the input string.
076     * @return the given string trimmed and converter to lower-case.
077     */
078    protected static String toString(final Object value) {
079        return Objects.requireNonNull(value, "value").toString();
080    }
081
082    /**
083     * Converts the given object to a lower-case string.
084     *
085     * @param value the input string.
086     * @return the given string trimmed and converter to lower-case.
087     */
088    protected static String toTrim(final Object value) {
089        return toString(value).trim();
090    }
091
092    /**
093     * Logging for this instance.
094     */
095    private transient Log log;
096
097    /**
098     * Should we return the default value on conversion errors?
099     */
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 --&gt; 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}