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Tools to assist in the reading of configuration/preferences files in
various formats
/*
* 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.configuration2.convert;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import org.apache.commons.configuration2.ex.ConversionException;
import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
import org.apache.commons.lang3.ClassUtils;
/**
*
* A default implementation of the {@code ConversionHandler} interface.
*
*
* This class implements the standard data type conversions as used by
* {@code AbstractConfiguration} and derived classes. There is a central
* conversion method - {@code convert()} - for converting a passed in object to
* a given target class. The basic implementation already handles a bunch of
* standard data type conversions. If other conversions are to be supported,
* this method can be overridden.
*
*
* The object passed to {@code convert()} can be a single value or a complex
* object (like an array, a collection, etc.) containing multiple values. It
* lies in the responsibility of {@code convert()} to deal with such complex
* objects. The implementation provided by this class tries to extract the first
* child element and then delegates to {@code convertValue()} which does the
* actual conversion.
*
*
* @since 2.0
*/
public class DefaultConversionHandler implements ConversionHandler
{
/**
* A default instance of this class. Because an instance of this class can
* be shared between arbitrary objects it is possible to make use of this
* default instance anywhere.
*/
public static final DefaultConversionHandler INSTANCE =
new DefaultConversionHandler();
/** The default format for dates. */
public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd HH:mm:ss";
/** A helper object used for extracting values from complex objects. */
private static final AbstractListDelimiterHandler EXTRACTOR =
(AbstractListDelimiterHandler) DisabledListDelimiterHandler.INSTANCE;
/**
* Constant for a default {@code ConfigurationInterpolator} to be used if
* none is provided by the caller.
*/
private static final ConfigurationInterpolator NULL_INTERPOLATOR =
new ConfigurationInterpolator()
{
@Override
public Object interpolate(final Object value)
{
return value;
}
};
/** The current date format. */
private volatile String dateFormat;
/**
* Returns the date format used by this conversion handler.
*
* @return the date format
*/
public String getDateFormat()
{
final String fmt = dateFormat;
return fmt != null ? fmt : DEFAULT_DATE_FORMAT;
}
/**
* Sets the date format to be used by this conversion handler. This format
* is applied by conversions to {@code Date} or {@code Calendar} objects.
* The string is passed to the {@code java.text.SimpleDateFormat} class, so
* it must be compatible with this class. If no date format has been set, a
* default format is used.
*
* @param dateFormat the date format string
* @see #DEFAULT_DATE_FORMAT
*/
public void setDateFormat(final String dateFormat)
{
this.dateFormat = dateFormat;
}
@Override
public T to(final Object src, final Class targetCls, final ConfigurationInterpolator ci)
{
final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
return convert(interpolator.interpolate(src), targetCls, interpolator);
}
/**
* {@inheritDoc} This implementation extracts all values stored in the
* passed in source object, converts them to the target type, and adds them
* to a result array. Arrays of objects and of primitive types are
* supported. If the source object is null, result is null,
* too.
*/
@Override
public Object toArray(final Object src, final Class elemClass,
final ConfigurationInterpolator ci)
{
if (src == null)
{
return null;
}
if (isEmptyElement(src))
{
return Array.newInstance(elemClass, 0);
}
final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
return elemClass.isPrimitive() ? toPrimitiveArray(src, elemClass,
interpolator) : toObjectArray(src, elemClass, interpolator);
}
/**
* {@inheritDoc} This implementation extracts all values stored in the
* passed in source object, converts them to the target type, and adds them
* to the target collection. The target collection must not be null.
* If the source object is null, nothing is added to the collection.
*
* @throws IllegalArgumentException if the target collection is null
*/
@Override
public void toCollection(final Object src, final Class elemClass,
final ConfigurationInterpolator ci, final Collection dest)
{
if (dest == null)
{
throw new IllegalArgumentException(
"Target collection must not be null!");
}
if (src != null && !isEmptyElement(src))
{
final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
convertToCollection(src, elemClass, interpolator, dest);
}
}
/**
* Tests whether the passed in object is complex (which means that it
* contains multiple values). This method is called by
* {@link #convert(Object, Class, ConfigurationInterpolator)} to figure out
* whether a actions are required to extract a single value from a complex
* source object. This implementation considers the following objects as
* complex:
*
* - {@code Iterable} objects
* - {@code Iterator} objects
* - Arrays
*
*
* @param src the source object
* @return true if this is a complex object, false otherwise
*/
protected boolean isComplexObject(final Object src)
{
return src instanceof Iterator || src instanceof Iterable
|| (src != null && src.getClass().isArray());
}
/**
* Tests whether the passed in object represents an empty element. This
* method is called by conversion methods to arrays or collections. If it
* returns true, the resulting array or collection will be empty.
* This implementation returns true if and only if the passed in
* object is an empty string. With this method it can be controlled if and
* how empty elements in configurations are handled.
*
* @param src the object to be tested
* @return a flag whether this object is an empty element
*/
protected boolean isEmptyElement(final Object src)
{
return (src instanceof CharSequence)
&& ((CharSequence) src).length() == 0;
}
/**
* Performs the conversion from the passed in source object to the specified
* target class. This method is called for each conversion to be done. The
* source object has already been passed to the
* {@link ConfigurationInterpolator}, so interpolation does not have to be
* done again. (The passed in {@code ConfigurationInterpolator} may still be
* necessary for extracting values from complex objects; it is guaranteed to
* be non null.) The source object may be a complex object, e.g. a
* collection or an array. This base implementation checks whether the
* source object is complex. If so, it delegates to
* {@link #extractConversionValue(Object, Class, ConfigurationInterpolator)}
* to obtain a single value. Eventually,
* {@link #convertValue(Object, Class, ConfigurationInterpolator)} is called
* with the single value to be converted.
*
* @param the desired target type of the conversion
* @param src the source object to be converted
* @param targetCls the desired target class
* @param ci the {@code ConfigurationInterpolator} (not null)
* @return the converted value
* @throws ConversionException if conversion is not possible
*/
protected T convert(final Object src, final Class targetCls,
final ConfigurationInterpolator ci)
{
final Object conversionSrc =
isComplexObject(src) ? extractConversionValue(src, targetCls,
ci) : src;
return convertValue(ci.interpolate(conversionSrc), targetCls, ci);
}
/**
* Extracts a maximum number of values contained in the given source object
* and returns them as flat collection. This method is useful if the caller
* only needs a subset of values, e.g. only the first one.
*
* @param source the source object (may be a single value or a complex
* object)
* @param limit the number of elements to extract
* @return a collection with all extracted values
*/
protected Collection extractValues(final Object source, final int limit)
{
return EXTRACTOR.flatten(source, limit);
}
/**
* Extracts all values contained in the given source object and returns them
* as a flat collection.
*
* @param source the source object (may be a single value or a complex
* object)
* @return a collection with all extracted values
*/
protected Collection extractValues(final Object source)
{
return extractValues(source, Integer.MAX_VALUE);
}
/**
* Extracts a single value from a complex object. This method is called by
* {@code convert()} if the source object is complex. This implementation
* extracts the first value from the complex object and returns it.
*
* @param container the complex object
* @param targetCls the target class of the conversion
* @param ci the {@code ConfigurationInterpolator} (not null)
* @return the value to be converted (may be null if no values are
* found)
*/
protected Object extractConversionValue(final Object container,
final Class targetCls, final ConfigurationInterpolator ci)
{
final Collection values = extractValues(container, 1);
return values.isEmpty() ? null : ci.interpolate(values.iterator()
.next());
}
/**
* Performs a conversion of a single value to the specified target class.
* The passed in source object is guaranteed to be a single value, but it
* can be null. Derived classes that want to extend the available
* conversions, but are happy with the handling of complex objects, just
* need to override this method.
*
* @param the desired target type of the conversion
* @param src the source object (a single value)
* @param targetCls the target class of the conversion
* @param ci the {@code ConfigurationInterpolator} (not null)
* @return the converted value
* @throws ConversionException if conversion is not possible
*/
protected T convertValue(final Object src, final Class targetCls,
final ConfigurationInterpolator ci)
{
if (src == null)
{
return null;
}
// This is a safe cast because PropertyConverter either returns an
// object of the correct class or throws an exception.
@SuppressWarnings("unchecked")
final
T result = (T) PropertyConverter.to(targetCls, src,
this);
return result;
}
/**
* Converts the given source object to an array of objects.
*
* @param src the source object
* @param elemClass the element class of the array
* @param ci the {@code ConfigurationInterpolator}
* @return the result array
* @throws ConversionException if a conversion cannot be performed
*/
private T[] toObjectArray(final Object src, final Class elemClass,
final ConfigurationInterpolator ci)
{
final Collection convertedCol = new LinkedList<>();
convertToCollection(src, elemClass, ci, convertedCol);
// Safe to cast because the element class is specified
@SuppressWarnings("unchecked")
final
T[] result = (T[]) Array.newInstance(elemClass, convertedCol.size());
return convertedCol.toArray(result);
}
/**
* Converts the given source object to an array of a primitive type. This
* method performs some checks whether the source object is already an array
* of the correct type or a corresponding wrapper type. If not, all values
* are extracted, converted one by one, and stored in a newly created array.
*
* @param src the source object
* @param elemClass the element class of the array
* @param ci the {@code ConfigurationInterpolator}
* @return the result array
* @throws ConversionException if a conversion cannot be performed
*/
private Object toPrimitiveArray(final Object src, final Class elemClass,
final ConfigurationInterpolator ci)
{
if (src.getClass().isArray())
{
if (src.getClass().getComponentType().equals(elemClass))
{
return src;
}
if (src.getClass().getComponentType()
.equals(ClassUtils.primitiveToWrapper(elemClass)))
{
// the value is an array of the wrapper type derived from the
// specified primitive type
final int length = Array.getLength(src);
final Object array = Array.newInstance(elemClass, length);
for (int i = 0; i < length; i++)
{
Array.set(array, i, Array.get(src, i));
}
return array;
}
}
final Collection values = extractValues(src);
final Class targetClass = ClassUtils.primitiveToWrapper(elemClass);
final Object array = Array.newInstance(elemClass, values.size());
int idx = 0;
for (final Object value : values)
{
Array.set(array, idx++,
convertValue(ci.interpolate(value), targetClass, ci));
}
return array;
}
/**
* Helper method for converting all values of a source object and storing
* them in a collection.
*
* @param the target type of the conversion
* @param src the source object
* @param elemClass the target class of the conversion
* @param ci the {@code ConfigurationInterpolator}
* @param dest the collection in which to store the results
* @throws ConversionException if a conversion cannot be performed
*/
private void convertToCollection(final Object src, final Class elemClass,
final ConfigurationInterpolator ci, final Collection dest)
{
for (final Object o : extractValues(ci.interpolate(src)))
{
dest.add(convert(o, elemClass, ci));
}
}
/**
* Obtains a {@code ConfigurationInterpolator}. If the passed in one is not
* null, it is used. Otherwise, a default one is returned.
*
* @param ci the {@code ConfigurationInterpolator} provided by the caller
* @return the {@code ConfigurationInterpolator} to be used
*/
private static ConfigurationInterpolator fetchInterpolator(
final ConfigurationInterpolator ci)
{
return ci != null ? ci : NULL_INTERPOLATOR;
}
}