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.beanutils.converters;
018
019import java.lang.reflect.Array;
020import java.util.Collection;
021import org.apache.commons.logging.Log;
022import org.apache.commons.logging.LogFactory;
023import org.apache.commons.beanutils.BeanUtils;
024import org.apache.commons.beanutils.ConversionException;
025import org.apache.commons.beanutils.Converter;
026
027/**
028 * Base {@link Converter} implementation that provides the structure
029 * for handling conversion <b>to</b> and <b>from</b> a specified type.
030 * <p>
031 * This implementation provides the basic structure for
032 * converting to/from a specified type optionally using a default
033 * value or throwing a {@link ConversionException} if a
034 * conversion error occurs.
035 * <p>
036 * Implementations should provide conversion to the specified
037 * type and from the specified type to a <code>String</code> value
038 * by implementing the following methods:
039 * <ul>
040 *     <li><code>convertToString(value)</code> - convert to a String
041 *        (default implementation uses the objects <code>toString()</code>
042 *        method).</li>
043 *     <li><code>convertToType(Class, value)</code> - convert
044 *         to the specified type</li>
045 * </ul>
046 *
047 * @version $Revision: 640131 $ $Date: 2008-03-23 02:10:31 +0000 (Sun, 23 Mar 2008) $
048 * @since 1.8.0
049 */
050public abstract class AbstractConverter implements Converter {
051
052    /** Debug logging message to indicate default value configuration */
053    private static final String DEFAULT_CONFIG_MSG =
054        "(N.B. Converters can be configured to use default values to avoid throwing exceptions)";
055
056    /** Current package name */
057    //    getPackage() below returns null on some platforms/jvm versions during the unit tests.
058//    private static final String PACKAGE = AbstractConverter.class.getPackage().getName() + ".";
059    private static final String PACKAGE = "org.apache.commons.beanutils.converters.";
060
061    /**
062     * Logging for this instance.
063     */
064    private transient Log log;
065
066    /**
067     * Should we return the default value on conversion errors?
068     */
069    private boolean useDefault = false;
070
071    /**
072     * The default value specified to our Constructor, if any.
073     */
074    private Object defaultValue = null;
075
076    // ----------------------------------------------------------- Constructors
077
078    /**
079     * Construct a <i>Converter</i> that throws a
080     * <code>ConversionException</code> if an error occurs.
081     */
082    public AbstractConverter() {
083    }
084
085    /**
086     * Construct a <i>Converter</i> that returns a default
087     * value if an error occurs.
088     *
089     * @param defaultValue The default value to be returned
090     * if the value to be converted is missing or an error
091     * occurs converting the value.
092     */
093    public AbstractConverter(Object defaultValue) {
094        setDefaultValue(defaultValue);
095    }
096
097    // --------------------------------------------------------- Public Methods
098
099    /**
100     * Indicates whether a default value will be returned or exception
101     * thrown in the event of a conversion error.
102     *
103     * @return <code>true</code> if a default value will be returned for
104     * conversion errors or <code>false</code> if a {@link ConversionException}
105     * will be thrown.
106     */
107    public boolean isUseDefault() {
108        return useDefault;
109    }
110
111    /**
112     * Convert the input object into an output object of the
113     * specified type.
114     *
115     * @param type Data type to which this value should be converted
116     * @param value The input value to be converted
117     * @return The converted value.
118     * @throws ConversionException if conversion cannot be performed
119     * successfully and no default is specified.
120     */
121    public Object convert(Class type, Object value) {
122
123        Class sourceType  = value == null ? null : value.getClass();
124        Class targetType  = primitive(type  == null ? getDefaultType() : type);
125
126        if (log().isDebugEnabled()) {
127            log().debug("Converting"
128                    + (value == null ? "" : " '" + toString(sourceType) + "'")
129                    + " value '" + value + "' to type '" + toString(targetType) + "'");
130        }
131
132        value = convertArray(value);
133
134        // Missing Value
135        if (value == null) {
136            return handleMissing(targetType);
137        }
138
139        sourceType = value.getClass();
140
141        try {
142            // Convert --> String
143            if (targetType.equals(String.class)) {
144                return convertToString(value);
145
146            // No conversion necessary
147            } else if (targetType.equals(sourceType)) {
148                if (log().isDebugEnabled()) {
149                    log().debug("    No conversion required, value is already a "
150                                    + toString(targetType));
151                }
152                return value;
153
154            // Convert --> Type
155            } else {
156                Object result = convertToType(targetType, value);
157                if (log().isDebugEnabled()) {
158                    log().debug("    Converted to " + toString(targetType) +
159                                   " value '" + result + "'");
160                }
161                return result;
162            }
163        } catch (Throwable t) {
164            return handleError(targetType, value, t);
165        }
166
167    }
168
169    /**
170     * Convert the input object into a String.
171     * <p>
172     * <b>N.B.</b>This implementation simply uses the value's
173     * <code>toString()</code> method and should be overriden if a
174     * more sophisticated mechanism for <i>conversion to a String</i>
175     * is required.
176     *
177     * @param value The input value to be converted.
178     * @return the converted String value.
179     * @throws Throwable if an error occurs converting to a String
180     */
181    protected String convertToString(Object value) throws Throwable {
182        return value.toString();
183    }
184
185    /**
186     * Convert the input object into an output object of the
187     * specified type.
188     * <p>
189     * Typical implementations will provide a minimum of
190     * <code>String --> type</code> conversion.
191     *
192     * @param type Data type to which this value should be converted.
193     * @param value The input value to be converted.
194     * @return The converted value.
195     * @throws Throwable if an error occurs converting to the specified type
196     */
197    protected abstract Object convertToType(Class type, Object value) throws Throwable;
198
199    /**
200     * Return the first element from an Array (or Collection)
201     * or the value unchanged if not an Array (or Collection).
202     *
203     * N.B. This needs to be overriden for array/Collection converters.
204     *
205     * @param value The value to convert
206     * @return The first element in an Array (or Collection)
207     * or the value unchanged if not an Array (or Collection)
208     */
209    protected Object convertArray(Object value) {
210        if (value == null) {
211            return null;
212        }
213        if (value.getClass().isArray()) {
214            if (Array.getLength(value) > 0) {
215                return Array.get(value, 0);
216            } else {
217                return null;
218            }
219        }
220        if (value instanceof Collection) {
221            Collection collection = (Collection)value;
222            if (collection.size() > 0) {
223                return collection.iterator().next();
224            } else {
225                return null;
226            }
227        }
228        return value;
229    }
230
231    /**
232     * Handle Conversion Errors.
233     * <p>
234     * If a default value has been specified then it is returned
235     * otherwise a ConversionException is thrown.
236     *
237     * @param type Data type to which this value should be converted.
238     * @param value The input value to be converted
239     * @param cause The exception thrown by the <code>convert</code> method
240     * @return The default value.
241     * @throws ConversionException if no default value has been
242     * specified for this {@link Converter}.
243     */
244    protected Object handleError(Class type, Object value, Throwable cause) {
245        if (log().isDebugEnabled()) {
246            if (cause instanceof ConversionException) {
247                log().debug("    Conversion threw ConversionException: " + cause.getMessage());
248            } else {
249                log().debug("    Conversion threw " + cause);
250            }
251        }
252
253        if (useDefault) {
254            return handleMissing(type);
255        }
256
257        ConversionException cex = null;
258        if (cause instanceof ConversionException) {
259            cex = (ConversionException)cause;
260            if (log().isDebugEnabled()) {
261                log().debug("    Re-throwing ConversionException: " + cex.getMessage());
262                log().debug("    " + DEFAULT_CONFIG_MSG);
263            }
264        } else {
265            String msg = "Error converting from '" + toString(value.getClass()) +
266                    "' to '" + toString(type) + "' " + cause.getMessage();
267            cex = new ConversionException(msg, cause);
268            if (log().isDebugEnabled()) {
269                log().debug("    Throwing ConversionException: " + msg);
270                log().debug("    " + DEFAULT_CONFIG_MSG);
271            }
272            BeanUtils.initCause(cex, cause);
273        }
274
275        throw cex;
276
277    }
278
279    /**
280     * Handle missing values.
281     * <p>
282     * If a default value has been specified then it is returned
283     * otherwise a ConversionException is thrown.
284     *
285     * @param type Data type to which this value should be converted.
286     * @return The default value.
287     * @throws ConversionException if no default value has been
288     * specified for this {@link Converter}.
289     */
290    protected Object handleMissing(Class type) {
291
292        if (useDefault || type.equals(String.class)) {
293            Object value = getDefault(type);
294            if (useDefault && value != null && !(type.equals(value.getClass()))) {
295                try {
296                    value = convertToType(type, defaultValue);
297                } catch (Throwable t) {
298                    log().error("    Default conversion to " + toString(type)
299                            + "failed: " + t);
300                }
301            }
302            if (log().isDebugEnabled()) {
303                log().debug("    Using default "
304                        + (value == null ? "" : toString(value.getClass()) + " ")
305                        + "value '" + defaultValue + "'");
306            }
307            return value;
308        }
309
310        ConversionException cex =  new ConversionException("No value specified for '" +
311                toString(type) + "'");
312        if (log().isDebugEnabled()) {
313            log().debug("    Throwing ConversionException: " + cex.getMessage());
314            log().debug("    " + DEFAULT_CONFIG_MSG);
315        }
316        throw cex;
317
318    }
319
320    /**
321     * Set the default value, converting as required.
322     * <p>
323     * If the default value is different from the type the
324     * <code>Converter</code> handles, it will be converted
325     * to the handled type.
326     *
327     * @param defaultValue The default value to be returned
328     * if the value to be converted is missing or an error
329     * occurs converting the value.
330     * @throws ConversionException if an error occurs converting
331     * the default value
332     */
333    protected void setDefaultValue(Object defaultValue) {
334        useDefault = false;
335        if (log().isDebugEnabled()) {
336            log().debug("Setting default value: " + defaultValue);
337        }
338        if (defaultValue == null) {
339           this.defaultValue  = null;
340        } else {
341           this.defaultValue  = convert(getDefaultType(), defaultValue);
342        }
343        useDefault = true;
344    }
345
346    /**
347     * Return the default type this <code>Converter</code> handles.
348     *
349     * @return The default type this <code>Converter</code> handles.
350     */
351    protected abstract Class getDefaultType();
352
353    /**
354     * Return the default value for conversions to the specified
355     * type.
356     * @param type Data type to which this value should be converted.
357     * @return The default value for the specified type.
358     */
359    protected Object getDefault(Class type) {
360        if (type.equals(String.class)) {
361            return null;
362        } else {
363            return defaultValue;
364        }
365    }
366    
367    /**
368     * Provide a String representation of this converter.
369     *
370     * @return A String representation of this converter
371     */
372    public String toString() {
373        return toString(getClass()) + "[UseDefault=" + useDefault + "]";
374    }
375
376    // ----------------------------------------------------------- Package Methods
377
378    /**
379     * Accessor method for Log instance.
380     * <p>
381     * The Log instance variable is transient and
382     * accessing it through this method ensures it
383     * is re-initialized when this instance is
384     * de-serialized.
385     *
386     * @return The Log instance.
387     */
388    Log log() {
389        if (log == null) {
390            log = LogFactory.getLog(getClass());
391        }
392        return log;
393    }
394
395    /**
396     * Change primitve Class types to the associated wrapper class.
397     * @param type The class type to check.
398     * @return The converted type.
399     */
400     Class primitive(Class type) {
401        if (type == null || !type.isPrimitive()) {
402            return type;
403        }
404
405        if (type == Integer.TYPE) {
406            return Integer.class;
407        } else if (type == Double.TYPE) {
408            return Double.class;
409        } else if (type == Long.TYPE) {
410            return Long.class;
411        } else if (type == Boolean.TYPE) {
412            return Boolean.class;
413        } else if (type == Float.TYPE) {
414            return Float.class;
415        } else if (type == Short.TYPE) {
416            return Short.class;
417        } else if (type == Byte.TYPE) {
418            return Byte.class;
419        } else if (type == Character.TYPE) {
420            return Character.class;
421        } else {
422            return type;
423        }
424    }
425
426    /**
427     * Provide a String representation of a <code>java.lang.Class</code>.
428     * @param type The <code>java.lang.Class</code>.
429     * @return The String representation.
430     */
431    String toString(Class type) {
432        String typeName = null;
433        if (type == null) {
434            typeName = "null";
435        } else if (type.isArray()) {
436            Class elementType = type.getComponentType();
437            int count = 1;
438            while (elementType.isArray()) {
439                elementType = elementType .getComponentType();
440                count++;
441            }
442            typeName = elementType.getName();
443            for (int i = 0; i < count; i++) {
444                typeName += "[]";
445            }
446        } else {
447            typeName = type.getName();
448        }
449        if (typeName.startsWith("java.lang.") ||
450            typeName.startsWith("java.util.") ||
451            typeName.startsWith("java.math.")) {
452            typeName = typeName.substring("java.lang.".length());
453        } else if (typeName.startsWith(PACKAGE)) {
454            typeName = typeName.substring(PACKAGE.length());
455        }
456        return typeName;
457    }
458}