AbstractConverter.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.beanutils2.converters;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Locale;
import java.util.Objects;
import org.apache.commons.beanutils2.ConversionException;
import org.apache.commons.beanutils2.ConvertUtils;
import org.apache.commons.beanutils2.Converter;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Base {@link Converter} implementation that provides the structure for handling conversion <strong>to</strong> and <strong>from</strong> a specified type.
* <p>
* This implementation provides the basic structure for converting to/from a specified type optionally using a default value or throwing a
* {@link ConversionException} if a conversion error occurs.
* </p>
* <p>
* Implementations should provide conversion to the specified type and from the specified type to a {@code String} value by implementing the following methods:
* </p>
* <ul>
* <li>{@code convertToString(value)} - convert to a String (default implementation uses the objects {@code toString()} method).</li>
* <li>{@code convertToType(Class, value)} - convert to the specified type</li>
* </ul>
* <p>
* 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
* possible and a default value is set, the converter tries to transform the default value to the requested target type. If this fails, a
* {@code ConversionException} if thrown.
* </p>
*
* @param <D> The default value type.
* @since 1.8.0
*/
public abstract class AbstractConverter<D> implements Converter<D> {
/** Debug logging message to indicate default value configuration */
private static final String DEFAULT_CONFIG_MSG = "(N.B. Converters can be configured to use default values to avoid throwing exceptions)";
/** Current package name */
// getPackage() below returns null on some platforms/jvm versions during the unit tests.
// private static final String PACKAGE = AbstractConverter.class.getPackage().getName() + ".";
private static final String PACKAGE = "org.apache.commons.beanutils2.converters.";
/**
* Converts the given object to a lower-case string.
*
* @param value the input string.
* @return the given string trimmed and converter to lower-case.
*/
protected static String toLowerCase(final Object value) {
return toString(value).toLowerCase(Locale.ROOT);
}
/**
* Converts the given object to a lower-case string.
*
* @param value the input string.
* @return the given string trimmed and converter to lower-case.
*/
protected static String toString(final Object value) {
return Objects.requireNonNull(value, "value").toString();
}
/**
* Converts the given object to a lower-case string.
*
* @param value the input string.
* @return the given string trimmed and converter to lower-case.
*/
protected static String toTrim(final Object value) {
return toString(value).trim();
}
/**
* Logging for this instance.
*/
private transient Log log;
/**
* Should we return the default value on conversion errors?
*/
private boolean useDefault;
/**
* The default value specified to our Constructor, if any.
*/
private D defaultValue;
/**
* Constructs a <em>Converter</em> that throws a {@code ConversionException} if an error occurs.
*/
public AbstractConverter() {
}
/**
* Constructs a <em>Converter</em> that returns a default value if an error occurs.
*
* @param defaultValue The default value to be returned if the value to be converted is missing or an error occurs converting the value.
*/
public AbstractConverter(final D defaultValue) {
setDefaultValue(defaultValue);
}
/**
* Creates a standard conversion exception with a message indicating that the passed in value cannot be converted to the desired target type.
*
* @param type the target type
* @param value the value to be converted
* @return a {@code ConversionException} with a standard message
* @since 1.9
*/
protected ConversionException conversionException(final Class<?> type, final Object value) {
return ConversionException.format("Can't convert value '%s' to type %s", value, type);
}
/**
* Converts the input object into an output object of the specified type.
*
* @param type Data type to which this value should be converted
* @param value The input value to be converted
* @return The converted value.
* @throws ConversionException if conversion cannot be performed successfully and no default is specified.
*/
@Override
public <R> R convert(final Class<R> type, Object value) {
if (type == null) {
return convertToDefaultType(value);
}
Class<?> sourceType = value == null ? null : value.getClass();
final Class<R> targetType = ConvertUtils.primitiveToWrapper(type);
if (log().isDebugEnabled()) {
log().debug(
"Converting" + (value == null ? "" : " '" + toString(sourceType) + "'") + " value '" + value + "' to type '" + toString(targetType) + "'");
}
value = convertArray(value);
// Missing Value
if (value == null) {
return handleMissing(targetType);
}
sourceType = value.getClass();
try {
// Convert --> String
if (targetType.equals(String.class)) {
return targetType.cast(convertToString(value));
// No conversion necessary
}
if (targetType.equals(sourceType)) {
if (log().isDebugEnabled()) {
log().debug(" No conversion required, value is already a " + toString(targetType));
}
return targetType.cast(value);
// Convert --> Type
}
final Object result = convertToType(targetType, value);
if (log().isDebugEnabled()) {
log().debug(" Converted to " + toString(targetType) + " value '" + result + "'");
}
return targetType.cast(result);
} catch (final Throwable t) {
return handleError(targetType, value, t);
}
}
/**
* Returns the first element from an Array (or Collection) or the value unchanged if not an Array (or Collection).
*
* N.B. This needs to be overridden for array/Collection converters.
*
* @param value The value to convert
* @return The first element in an Array (or Collection) or the value unchanged if not an Array (or Collection)
*/
protected Object convertArray(final Object value) {
if (value == null) {
return null;
}
if (value.getClass().isArray()) {
if (Array.getLength(value) > 0) {
return Array.get(value, 0);
}
return null;
}
if (value instanceof Collection) {
final Collection<?> collection = (Collection<?>) value;
if (!collection.isEmpty()) {
return collection.iterator().next();
}
return null;
}
return value;
}
/**
* 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
* it (which is required to fulfill the contract of the method signature).
*
* @param value the value to be converted
* @param <T> the type of the result object
* @return the converted value
*/
@SuppressWarnings("unchecked")
private <T> T convertToDefaultType(final Object value) {
return (T) convert(getDefaultType(), value);
}
/**
* Converts the input object into a String.
* <p>
* <strong>N.B.</strong>This implementation simply uses the value's {@code toString()} method and should be overridden if a more sophisticated mechanism for
* <em>conversion to a String</em> is required.
* </p>
*
* @param value The input value to be converted.
* @return the converted String value.
* @throws IllegalArgumentException if an error occurs converting to a String
*/
protected String convertToString(final Object value) {
return value.toString();
}
/**
* Converts the input object into an output object of the specified type.
* <p>
* Typical implementations will provide a minimum of {@code String --> type} conversion.
* </p>
*
* @param <R> Target type of the conversion.
* @param type Data type to which this value should be converted.
* @param value The input value to be converted.
* @return The converted value.
* @throws Throwable if an error occurs converting to the specified type
*/
protected abstract <R> R convertToType(Class<R> type, Object value) throws Throwable;
/**
* Gets the default value for conversions to the specified type.
*
* @param type Data type to which this value should be converted.
* @return The default value for the specified type.
*/
protected Object getDefault(final Class<?> type) {
if (type.equals(String.class)) {
return null;
}
return defaultValue;
}
/**
* Gets the default type this {@code Converter} handles.
*
* @return The default type this {@code Converter} handles.
*/
protected abstract Class<D> getDefaultType();
/**
* Handles Conversion Errors.
* <p>
* If a default value has been specified then it is returned otherwise a ConversionException is thrown.
* </p>
*
* @param <T> Target type of the conversion.
* @param type Data type to which this value should be converted.
* @param value The input value to be converted
* @param cause The exception thrown by the {@code convert} method
* @return The default value.
* @throws ConversionException if no default value has been specified for this {@link Converter}.
*/
protected <T> T handleError(final Class<T> type, final Object value, final Throwable cause) {
if (log().isDebugEnabled()) {
if (cause instanceof ConversionException) {
log().debug(" Conversion threw ConversionException: " + cause.getMessage());
} else {
log().debug(" Conversion threw " + cause);
}
}
if (useDefault) {
return handleMissing(type);
}
ConversionException cex = null;
if (cause instanceof ConversionException) {
cex = (ConversionException) cause;
if (log().isDebugEnabled()) {
log().debug(" Re-throwing ConversionException: " + cex.getMessage());
log().debug(" " + DEFAULT_CONFIG_MSG);
}
} else {
final String msg = "Error converting from '" + toString(value.getClass()) + "' to '" + toString(type) + "' " + cause.getMessage();
cex = new ConversionException(msg, cause);
if (log().isDebugEnabled()) {
log().debug(" Throwing ConversionException: " + msg);
log().debug(" " + DEFAULT_CONFIG_MSG);
}
}
throw cex;
}
/**
* Handles missing values.
* <p>
* If a default value has been specified, then it is returned (after a cast to the desired target class); otherwise a ConversionException is thrown.
* </p>
*
* @param <T> the desired target type
* @param type Data type to which this value should be converted.
* @return The default value.
* @throws ConversionException if no default value has been specified for this {@link Converter}.
*/
protected <T> T handleMissing(final Class<T> type) {
if (useDefault || type.equals(String.class)) {
Object value = getDefault(type);
if (useDefault && value != null && !type.equals(value.getClass())) {
try {
value = convertToType(type, defaultValue);
} catch (final Throwable t) {
throw new ConversionException("Default conversion to " + toString(type) + " failed.", t);
}
}
if (log().isDebugEnabled()) {
log().debug(" Using default " + (value == null ? "" : toString(value.getClass()) + " ") + "value '" + defaultValue + "'");
}
// value is now either null or of the desired target type
return type.cast(value);
}
final ConversionException cex = ConversionException.format("No value specified for '%s'", toString(type));
if (log().isDebugEnabled()) {
log().debug(" Throwing ConversionException: " + cex.getMessage());
log().debug(" " + DEFAULT_CONFIG_MSG);
}
throw cex;
}
/**
* Tests whether a default value will be returned or exception thrown in the event of a conversion error.
*
* @return {@code true} if a default value will be returned for conversion errors or {@code false} if a {@link ConversionException} will be thrown.
*/
public boolean isUseDefault() {
return useDefault;
}
/**
* Gets the Log instance.
* <p>
* The Log instance variable is transient and accessing it through this method ensures it is re-initialized when this instance is de-serialized.
* </p>
*
* @return The Log instance.
*/
Log log() {
if (log == null) {
log = LogFactory.getLog(getClass());
}
return log;
}
/**
* Sets the default value, converting as required.
* <p>
* If the default value is different from the type the {@code Converter} handles, it will be converted to the handled type.
* </p>
*
* @param defaultValue The default value to be returned if the value to be converted is missing or an error occurs converting the value.
* @throws ConversionException if an error occurs converting the default value
*/
protected void setDefaultValue(final D defaultValue) {
useDefault = false;
if (log().isDebugEnabled()) {
log().debug("Setting default value: " + defaultValue);
}
if (defaultValue == null) {
this.defaultValue = null;
} else {
this.defaultValue = convert(getDefaultType(), defaultValue);
}
useDefault = true;
}
/**
* Converts this instance to a String.
*
* @return A String representation of this converter
*/
@Override
public String toString() {
return toString(getClass()) + "[UseDefault=" + useDefault + "]";
}
/**
* Converts a {@link Class} to a String.
*
* @param type The {@link Class}.
* @return The String representation.
*/
String toString(final Class<?> type) {
String typeName = null;
if (type == null) {
typeName = "null";
} else if (type.isArray()) {
Class<?> elementType = type.getComponentType();
int count = 1;
while (elementType.isArray()) {
elementType = elementType.getComponentType();
count++;
}
final StringBuilder typeNameBuilder = new StringBuilder(elementType.getName());
for (int i = 0; i < count; i++) {
typeNameBuilder.append("[]");
}
typeName = typeNameBuilder.toString();
} else {
typeName = type.getName();
}
if (typeName.startsWith("java.lang.") || typeName.startsWith("java.util.") || typeName.startsWith("java.math.")) {
typeName = typeName.substring("java.lang.".length());
} else if (typeName.startsWith(PACKAGE)) {
typeName = typeName.substring(PACKAGE.length());
}
return typeName;
}
}