    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}