org.apache.commons.beanutils.converters.AbstractConverter Maven / Gradle / Ivy
/*
* 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.beanutils.converters;
import java.lang.reflect.Array;
import java.util.Collection;
import org.apache.commons.beanutils.BeanUtils;
import org.apache.commons.beanutils.ConversionException;
import org.apache.commons.beanutils.ConvertUtils;
import org.apache.commons.beanutils.Converter;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Base {@link Converter} implementation that provides the structure
* for handling conversion to and from a specified type.
*
* 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.
*
* Implementations should provide conversion to the specified
* type and from the specified type to a String value
* by implementing the following methods:
*
* convertToString(value) - convert to a String
* (default implementation uses the objects toString()
* method).convertToType(Class, value) - convert
* to the specified type
*
* 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.
*
* @version $Id$
* @since 1.8.0
*/
public abstract class AbstractConverter implements Converter {
/** 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.beanutils.converters.";
/**
* Logging for this instance.
*/
private transient Log log;
/**
* Should we return the default value on conversion errors?
*/
private boolean useDefault = false;
/**
* The default value specified to our Constructor, if any.
*/
private Object defaultValue = null;
// ----------------------------------------------------------- Constructors
/**
* Construct a Converter that throws a
* ConversionException if an error occurs.
*/
public AbstractConverter() {
}
/**
* Construct a Converter 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 Object defaultValue) {
setDefaultValue(defaultValue);
}
// --------------------------------------------------------- Public Methods
/**
* Indicates whether a default value will be returned or exception
* thrown in the event of a conversion error.
*
* @return true if a default value will be returned for
* conversion errors or false if a {@link ConversionException}
* will be thrown.
*/
public boolean isUseDefault() {
return useDefault;
}
/**
* Convert the input object into an output object of the
* specified type.
*
* @param the 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 ConversionException if conversion cannot be performed
* successfully and no default is specified.
*/
public T convert(final Class type, Object value) {
if (type == null) {
return convertToDefaultType(type, value);
}
Class sourceType = value == null ? null : value.getClass();
final Class 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
} else if (targetType.equals(sourceType)) {
if (log().isDebugEnabled()) {
log().debug(" No conversion required, value is already a "
+ toString(targetType));
}
return targetType.cast(value);
// Convert --> Type
} else {
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);
}
}
/**
* Convert the input object into a String.
*
* N.B.This implementation simply uses the value's
* toString() method and should be overriden if a
* more sophisticated mechanism for conversion to a String
* is required.
*
* @param value The input value to be converted.
* @return the converted String value.
* @throws Throwable if an error occurs converting to a String
*/
protected String convertToString(final Object value) throws Throwable {
return value.toString();
}
/**
* Convert the input object into an output object of the
* specified type.
*
* Typical implementations will provide a minimum of
* String --> type conversion.
*
* @param 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 T convertToType(Class type, Object value) throws Throwable;
/**
* Return the first element from an Array (or Collection)
* or the value unchanged if not an Array (or Collection).
*
* N.B. This needs to be overriden 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);
} else {
return null;
}
}
if (value instanceof Collection) {
final Collection collection = (Collection)value;
if (collection.size() > 0) {
return collection.iterator().next();
} else {
return null;
}
}
return value;
}
/**
* Handle Conversion Errors.
*
* If a default value has been specified then it is returned
* otherwise a ConversionException is thrown.
*
* @param 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 convert method
* @return The default value.
* @throws ConversionException if no default value has been
* specified for this {@link Converter}.
*/
protected T handleError(final Class 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);
}
BeanUtils.initCause(cex, cause);
}
throw cex;
}
/**
* Handle missing values.
*
* If a default value has been specified, then it is returned (after a cast
* to the desired target class); otherwise a ConversionException is thrown.
*
* @param 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 handleMissing(final Class 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 = new ConversionException("No value specified for '" +
toString(type) + "'");
if (log().isDebugEnabled()) {
log().debug(" Throwing ConversionException: " + cex.getMessage());
log().debug(" " + DEFAULT_CONFIG_MSG);
}
throw cex;
}
/**
* Set the default value, converting as required.
*
* If the default value is different from the type the
* Converter handles, it will be converted
* to the handled type.
*
* @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 Object 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;
}
/**
* Return the default type this Converter handles.
*
* @return The default type this Converter handles.
*/
protected abstract Class getDefaultType();
/**
* Return 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;
} else {
return defaultValue;
}
}
/**
* Provide a String representation of this converter.
*
* @return A String representation of this converter
*/
@Override
public String toString() {
return toString(getClass()) + "[UseDefault=" + useDefault + "]";
}
// ----------------------------------------------------------- Package Methods
/**
* Accessor method for Log instance.
*
* The Log instance variable is transient and
* accessing it through this method ensures it
* is re-initialized when this instance is
* de-serialized.
*
* @return The Log instance.
*/
Log log() {
if (log == null) {
log = LogFactory.getLog(getClass());
}
return log;
}
/**
* Provide a String representation of a java.lang.Class.
* @param type The java.lang.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++;
}
typeName = elementType.getName();
for (int i = 0; i < count; i++) {
typeName += "[]";
}
} 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;
}
/**
* Performs a conversion 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 the type of the result object
* @param targetClass the target class of the conversion
* @param value the value to be converted
* @return the converted value
*/
private T convertToDefaultType(final Class targetClass, final Object value) {
@SuppressWarnings("unchecked")
final
T result = (T) convert(getDefaultType(), value);
return result;
}
/**
* Generates 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 new ConversionException("Can't convert value '" + value
+ "' to type " + type);
}
}