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/*
* 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 com.feilong.lib.beanutils.converters;
import java.lang.reflect.Array;
import java.util.Collection;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.feilong.lib.beanutils.ConversionException;
import com.feilong.lib.beanutils.ConvertUtils;
import com.feilong.lib.beanutils.Converter;
/**
* 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{
/** The Constant log. */
private static final Logger LOGGER = LoggerFactory.getLogger(AbstractConverter.class);
//---------------------------------------------------------------
/** 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.";
/**
* 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.
*/
@Override
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);
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)){
return targetType.cast(value);
// Convert --> Type
}else{
final Object result = convertToType(targetType, value);
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);
}
return null;
}
if (value instanceof Collection){
final Collection collection = (Collection) value;
if (collection.size() > 0){
return collection.iterator().next();
}
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 (LOGGER.isDebugEnabled()){
if (cause instanceof ConversionException){
LOGGER.debug(" Conversion threw ConversionException: " + cause.getMessage());
}else{
LOGGER.debug(" Conversion threw " + cause);
}
}
if (useDefault){
return handleMissing(type);
}
ConversionException cex = null;
if (cause instanceof ConversionException){
cex = (ConversionException) cause;
if (LOGGER.isDebugEnabled()){
LOGGER.debug(" Re-throwing ConversionException: " + cex.getMessage());
LOGGER.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 (LOGGER.isDebugEnabled()){
LOGGER.debug(" Throwing ConversionException: " + msg);
LOGGER.debug(" " + DEFAULT_CONFIG_MSG);
}
}
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 (LOGGER.isDebugEnabled()){
LOGGER.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 (LOGGER.isDebugEnabled()){
LOGGER.debug(" Throwing ConversionException: " + cex.getMessage());
LOGGER.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 (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;
}
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
/**
* 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);
}
}