    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;
    021
    022import org.apache.commons.beanutils.BeanUtils;
    023import org.apache.commons.beanutils.ConversionException;
    024import org.apache.commons.beanutils.ConvertUtils;
    025import org.apache.commons.beanutils.Converter;
    026import org.apache.commons.logging.Log;
    027import org.apache.commons.logging.LogFactory;
    028
    029/**
    030 * Base {@link Converter} implementation that provides the structure
    031 * for handling conversion <b>to</b> and <b>from</b> a specified type.
    032 * <p>
    033 * This implementation provides the basic structure for
    034 * converting to/from a specified type optionally using a default
    035 * value or throwing a {@link ConversionException} if a
    036 * conversion error occurs.
    037 * <p>
    038 * Implementations should provide conversion to the specified
    039 * type and from the specified type to a <code>String</code> value
    040 * by implementing the following methods:
    041 * <ul>
    042 *     <li><code>convertToString(value)</code> - convert to a String
    043 *        (default implementation uses the objects <code>toString()</code>
    044 *        method).</li>
    045 *     <li><code>convertToType(Class, value)</code> - convert
    046 *         to the specified type</li>
    047 * </ul>
    048 * <p>
    049 * The default value has to be compliant to the default type of this
    050 * converter - which is enforced by the generic type parameter. If a
    051 * conversion is not possible and a default value is set, the converter
    052 * tries to transform the default value to the requested target type.
    053 * If this fails, a {@code ConversionException} if thrown.
    054 *
    055 * @version $Id$
    056 * @since 1.8.0
    057 */
    058public abstract class AbstractConverter implements Converter {
    059
    060    /** Debug logging message to indicate default value configuration */
    061    private static final String DEFAULT_CONFIG_MSG =
    062        "(N.B. Converters can be configured to use default values to avoid throwing exceptions)";
    063
    064    /** Current package name */
    065    //    getPackage() below returns null on some platforms/jvm versions during the unit tests.
    066//    private static final String PACKAGE = AbstractConverter.class.getPackage().getName() + ".";
    067    private static final String PACKAGE = "org.apache.commons.beanutils.converters.";
    068
    069    /**
    070     * Logging for this instance.
    071     */
    072    private transient Log log;
    073
    074    /**
    075     * Should we return the default value on conversion errors?
    076     */
    077    private boolean useDefault = false;
    078
    079    /**
    080     * The default value specified to our Constructor, if any.
    081     */
    082    private Object defaultValue = null;
    083
    084    // ----------------------------------------------------------- Constructors
    085
    086    /**
    087     * Construct a <i>Converter</i> that throws a
    088     * <code>ConversionException</code> if an error occurs.
    089     */
    090    public AbstractConverter() {
    091    }
    092
    093    /**
    094     * Construct a <i>Converter</i> that returns a default
    095     * value if an error occurs.
    096     *
    097     * @param defaultValue The default value to be returned
    098     * if the value to be converted is missing or an error
    099     * occurs converting the value.
    100     */
    101    public AbstractConverter(final Object defaultValue) {
    102        setDefaultValue(defaultValue);
    103    }
    104
    105    // --------------------------------------------------------- Public Methods
    106
    107    /**
    108     * Indicates whether a default value will be returned or exception
    109     * thrown in the event of a conversion error.
    110     *
    111     * @return <code>true</code> if a default value will be returned for
    112     * conversion errors or <code>false</code> if a {@link ConversionException}
    113     * will be thrown.
    114     */
    115    public boolean isUseDefault() {
    116        return useDefault;
    117    }
    118
    119    /**
    120     * Convert the input object into an output object of the
    121     * specified type.
    122     *
    123     * @param <T> the target type of the conversion
    124     * @param type Data type to which this value should be converted
    125     * @param value The input value to be converted
    126     * @return The converted value.
    127     * @throws ConversionException if conversion cannot be performed
    128     * successfully and no default is specified.
    129     */
    130    public <T> T convert(final Class<T> type, Object value) {
    131
    132        if (type == null) {
    133            return convertToDefaultType(type, value);
    134        }
    135
    136        Class<?> sourceType  = value == null ? null : value.getClass();
    137        final Class<T> targetType  = ConvertUtils.primitiveToWrapper(type);
    138
    139        if (log().isDebugEnabled()) {
    140            log().debug("Converting"
    141                    + (value == null ? "" : " '" + toString(sourceType) + "'")
    142                    + " value '" + value + "' to type '" + toString(targetType) + "'");
    143        }
    144
    145        value = convertArray(value);
    146
    147        // Missing Value
    148        if (value == null) {
    149            return handleMissing(targetType);
    150        }
    151
    152        sourceType = value.getClass();
    153
    154        try {
    155            // Convert --> String
    156            if (targetType.equals(String.class)) {
    157                return targetType.cast(convertToString(value));
    158
    159            // No conversion necessary
    160            } else if (targetType.equals(sourceType)) {
    161                if (log().isDebugEnabled()) {
    162                    log().debug("    No conversion required, value is already a "
    163                                    + toString(targetType));
    164                }
    165                return targetType.cast(value);
    166
    167            // Convert --> Type
    168            } else {
    169                final Object result = convertToType(targetType, value);
    170                if (log().isDebugEnabled()) {
    171                    log().debug("    Converted to " + toString(targetType) +
    172                                   " value '" + result + "'");
    173                }
    174                return targetType.cast(result);
    175            }
    176        } catch (final Throwable t) {
    177            return handleError(targetType, value, t);
    178        }
    179
    180    }
    181
    182    /**
    183     * Convert the input object into a String.
    184     * <p>
    185     * <b>N.B.</b>This implementation simply uses the value's
    186     * <code>toString()</code> method and should be overriden if a
    187     * more sophisticated mechanism for <i>conversion to a String</i>
    188     * is required.
    189     *
    190     * @param value The input value to be converted.
    191     * @return the converted String value.
    192     * @throws Throwable if an error occurs converting to a String
    193     */
    194    protected String convertToString(final Object value) throws Throwable {
    195        return value.toString();
    196    }
    197
    198    /**
    199     * Convert the input object into an output object of the
    200     * specified type.
    201     * <p>
    202     * Typical implementations will provide a minimum of
    203     * <code>String --> type</code> conversion.
    204     *
    205     * @param <T> Target type of the conversion.
    206     * @param type Data type to which this value should be converted.
    207     * @param value The input value to be converted.
    208     * @return The converted value.
    209     * @throws Throwable if an error occurs converting to the specified type
    210     */
    211    protected abstract <T> T convertToType(Class<T> type, Object value) throws Throwable;
    212
    213    /**
    214     * Return the first element from an Array (or Collection)
    215     * or the value unchanged if not an Array (or Collection).
    216     *
    217     * N.B. This needs to be overriden for array/Collection converters.
    218     *
    219     * @param value The value to convert
    220     * @return The first element in an Array (or Collection)
    221     * or the value unchanged if not an Array (or Collection)
    222     */
    223    protected Object convertArray(final Object value) {
    224        if (value == null) {
    225            return null;
    226        }
    227        if (value.getClass().isArray()) {
    228            if (Array.getLength(value) > 0) {
    229                return Array.get(value, 0);
    230            } else {
    231                return null;
    232            }
    233        }
    234        if (value instanceof Collection) {
    235            final Collection<?> collection = (Collection<?>)value;
    236            if (collection.size() > 0) {
    237                return collection.iterator().next();
    238            } else {
    239                return null;
    240            }
    241        }
    242        return value;
    243    }
    244
    245    /**
    246     * Handle Conversion Errors.
    247     * <p>
    248     * If a default value has been specified then it is returned
    249     * otherwise a ConversionException is thrown.
    250     *
    251     * @param <T> Target type of the conversion.
    252     * @param type Data type to which this value should be converted.
    253     * @param value The input value to be converted
    254     * @param cause The exception thrown by the <code>convert</code> method
    255     * @return The default value.
    256     * @throws ConversionException if no default value has been
    257     * specified for this {@link Converter}.
    258     */
    259    protected <T> T handleError(final Class<T> type, final Object value, final Throwable cause) {
    260        if (log().isDebugEnabled()) {
    261            if (cause instanceof ConversionException) {
    262                log().debug("    Conversion threw ConversionException: " + cause.getMessage());
    263            } else {
    264                log().debug("    Conversion threw " + cause);
    265            }
    266        }
    267
    268        if (useDefault) {
    269            return handleMissing(type);
    270        }
    271
    272        ConversionException cex = null;
    273        if (cause instanceof ConversionException) {
    274            cex = (ConversionException)cause;
    275            if (log().isDebugEnabled()) {
    276                log().debug("    Re-throwing ConversionException: " + cex.getMessage());
    277                log().debug("    " + DEFAULT_CONFIG_MSG);
    278            }
    279        } else {
    280            final String msg = "Error converting from '" + toString(value.getClass()) +
    281                    "' to '" + toString(type) + "' " + cause.getMessage();
    282            cex = new ConversionException(msg, cause);
    283            if (log().isDebugEnabled()) {
    284                log().debug("    Throwing ConversionException: " + msg);
    285                log().debug("    " + DEFAULT_CONFIG_MSG);
    286            }
    287            BeanUtils.initCause(cex, cause);
    288        }
    289
    290        throw cex;
    291
    292    }
    293
    294    /**
    295     * Handle missing values.
    296     * <p>
    297     * If a default value has been specified, then it is returned (after a cast
    298     * to the desired target class); otherwise a ConversionException is thrown.
    299     *
    300     * @param <T> the desired target type
    301     * @param type Data type to which this value should be converted.
    302     * @return The default value.
    303     * @throws ConversionException if no default value has been
    304     * specified for this {@link Converter}.
    305     */
    306    protected <T> T handleMissing(final Class<T> type) {
    307
    308        if (useDefault || type.equals(String.class)) {
    309            Object value = getDefault(type);
    310            if (useDefault && value != null && !(type.equals(value.getClass()))) {
    311                try {
    312                    value = convertToType(type, defaultValue);
    313                } catch (final Throwable t) {
    314                    throw new ConversionException("Default conversion to " + toString(type)
    315                            + " failed.", t);
    316                }
    317            }
    318            if (log().isDebugEnabled()) {
    319                log().debug("    Using default "
    320                        + (value == null ? "" : toString(value.getClass()) + " ")
    321                        + "value '" + defaultValue + "'");
    322            }
    323            // value is now either null or of the desired target type
    324            return type.cast(value);
    325        }
    326
    327        final ConversionException cex =  new ConversionException("No value specified for '" +
    328                toString(type) + "'");
    329        if (log().isDebugEnabled()) {
    330            log().debug("    Throwing ConversionException: " + cex.getMessage());
    331            log().debug("    " + DEFAULT_CONFIG_MSG);
    332        }
    333        throw cex;
    334
    335    }
    336
    337    /**
    338     * Set the default value, converting as required.
    339     * <p>
    340     * If the default value is different from the type the
    341     * <code>Converter</code> handles, it will be converted
    342     * to the handled type.
    343     *
    344     * @param defaultValue The default value to be returned
    345     * if the value to be converted is missing or an error
    346     * occurs converting the value.
    347     * @throws ConversionException if an error occurs converting
    348     * the default value
    349     */
    350    protected void setDefaultValue(final Object defaultValue) {
    351        useDefault = false;
    352        if (log().isDebugEnabled()) {
    353            log().debug("Setting default value: " + defaultValue);
    354        }
    355        if (defaultValue == null) {
    356           this.defaultValue  = null;
    357        } else {
    358           this.defaultValue  = convert(getDefaultType(), defaultValue);
    359        }
    360        useDefault = true;
    361    }
    362
    363    /**
    364     * Return the default type this <code>Converter</code> handles.
    365     *
    366     * @return The default type this <code>Converter</code> handles.
    367     */
    368    protected abstract Class<?> getDefaultType();
    369
    370    /**
    371     * Return the default value for conversions to the specified
    372     * type.
    373     * @param type Data type to which this value should be converted.
    374     * @return The default value for the specified type.
    375     */
    376    protected Object getDefault(final Class<?> type) {
    377        if (type.equals(String.class)) {
    378            return null;
    379        } else  {
    380            return defaultValue;
    381        }
    382    }
    383
    384    /**
    385     * Provide a String representation of this converter.
    386     *
    387     * @return A String representation of this converter
    388     */
    389    @Override
    390    public String toString() {
    391        return toString(getClass()) + "[UseDefault=" + useDefault + "]";
    392    }
    393
    394    // ----------------------------------------------------------- Package Methods
    395
    396    /**
    397     * Accessor method for Log instance.
    398     * <p>
    399     * The Log instance variable is transient and
    400     * accessing it through this method ensures it
    401     * is re-initialized when this instance is
    402     * de-serialized.
    403     *
    404     * @return The Log instance.
    405     */
    406    Log log() {
    407        if (log == null) {
    408            log = LogFactory.getLog(getClass());
    409        }
    410        return log;
    411    }
    412
    413    /**
    414     * Provide a String representation of a <code>java.lang.Class</code>.
    415     * @param type The <code>java.lang.Class</code>.
    416     * @return The String representation.
    417     */
    418    String toString(final Class<?> type) {
    419        String typeName = null;
    420        if (type == null) {
    421            typeName = "null";
    422        } else if (type.isArray()) {
    423            Class<?> elementType = type.getComponentType();
    424            int count = 1;
    425            while (elementType.isArray()) {
    426                elementType = elementType .getComponentType();
    427                count++;
    428            }
    429            typeName = elementType.getName();
    430            for (int i = 0; i < count; i++) {
    431                typeName += "[]";
    432            }
    433        } else {
    434            typeName = type.getName();
    435        }
    436        if (typeName.startsWith("java.lang.") ||
    437            typeName.startsWith("java.util.") ||
    438            typeName.startsWith("java.math.")) {
    439            typeName = typeName.substring("java.lang.".length());
    440        } else if (typeName.startsWith(PACKAGE)) {
    441            typeName = typeName.substring(PACKAGE.length());
    442        }
    443        return typeName;
    444    }
    445
    446    /**
    447     * Performs a conversion to the default type. This method is called if we do
    448     * not have a target class. In this case, the T parameter is not set.
    449     * Therefore, we can cast to it (which is required to fulfill the contract
    450     * of the method signature).
    451     *
    452     * @param <T> the type of the result object
    453     * @param targetClass the target class of the conversion
    454     * @param value the value to be converted
    455     * @return the converted value
    456     */
    457    private <T> T convertToDefaultType(final Class<T> targetClass, final Object value) {
    458        @SuppressWarnings("unchecked")
    459        final
    460        T result = (T) convert(getDefaultType(), value);
    461        return result;
    462    }
    463
    464    /**
    465     * Generates a standard conversion exception with a message indicating that
    466     * the passed in value cannot be converted to the desired target type.
    467     *
    468     * @param type the target type
    469     * @param value the value to be converted
    470     * @return a {@code ConversionException} with a standard message
    471     * @since 1.9
    472     */
    473    protected ConversionException conversionException(final Class<?> type, final Object value) {
    474        return new ConversionException("Can't convert value '" + value
    475                + "' to type " + type);
    476    }
    477}