org.simpleframework.xml.core.CollectionFactory Maven / Gradle / Ivy
/*
* CollectionFactory.java July 2006
*
* Copyright (C) 2006, Niall Gallagher
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* Public License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307 USA
*/
package org.simpleframework.xml.core;
import org.simpleframework.xml.strategy.Value;
import org.simpleframework.xml.stream.InputNode;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.TreeSet;
/**
* The CollectionFactory is used to create collection
* instances that are compatible with the field type. This performs
* resolution of the collection class by firstly consulting the
* specified Strategy implementation. If the strategy
* cannot resolve the collection class then this will select a type
* from the Java Collections framework, if a compatible one exists.
*
* @author Niall Gallagher
*/
class CollectionFactory extends Factory {
/**
* Constructor for the CollectionFactory object. This
* is given the field type as taken from the owning object. The
* given type is used to determine the collection instance created.
*
* @param field this is the class for the owning object
*/
public CollectionFactory(Context context, Class field) {
super(context, field);
}
/**
* Creates a collection that is determined from the field type.
* This is used for the ElementList to get a
* collection that does not have any overrides. This must be
* done as the inline list does not contain an outer element.
*
* @return a type which is used to instantiate the collection
*/
@Override
public Object getInstance() throws Exception {
Class type = field;
if(!isInstantiable(type)) {
type = getConversion(field);
}
if(!isCollection(type)) {
throw new InstantiationException("Type is not a collection %s", field);
}
return type.newInstance();
}
/**
* Creates the collection to use. The Strategy object
* is consulted for the collection class, if one is not resolved
* by the strategy implementation or if the collection resolved is
* abstract then the Java Collections framework is consulted.
*
* @param node this is the input node representing the list
*
* @return this is the collection instantiated for the field
*/
public Instance getInstance(InputNode node) throws Exception {
Value value = getOverride(node);
if(value != null) {
return getInstance(value);
}
if(!isInstantiable(field)) {
field = getConversion(field);
}
if(!isCollection(field)) {
throw new InstantiationException("Type is not a collection %s", field);
}
return context.getInstance(field);
}
/**
* This creates a Collection instance from the type
* provided. If the type provided is abstract or an interface then
* this can promote the type to a collection type that can be
* instantiated. This is done by asking the type to convert itself.
*
* @param value the type used to instantiate the collection
*
* @return this returns a compatible collection instance
*/
public Instance getInstance(Value value) throws Exception {
Class type = value.getType();
if(!isInstantiable(type)) {
type = getConversion(type);
}
if(!isCollection(type)) {
throw new InstantiationException("Type is not a collection %s", type);
}
return new ConversionInstance(context, value, type);
}
/**
* This is used to convert the provided type to a collection type
* from the Java Collections framework. This will check to see if
* the type is a List or Set and return
* an ArrayList or HashSet type. If no
* suitable match can be found this throws an exception.
*
* @param type this is the type that is to be converted
*
* @return a collection that is assignable to the provided type
*/
public Class getConversion(Class type) throws Exception {
if(type.isAssignableFrom(ArrayList.class)) {
return ArrayList.class;
}
if(type.isAssignableFrom(HashSet.class)) {
return HashSet.class;
}
if(type.isAssignableFrom(TreeSet.class)) {
return TreeSet.class;
}
throw new InstantiationException("Cannot instantiate %s", type);
}
/**
* This determines whether the type provided is a collection type.
* If the type is assignable to a Collection then
* this returns true, otherwise this returns false.
*
* @param type given to determine whether it is a collection
*
* @return true if the provided type is a collection type
*/
private boolean isCollection(Class type) {
return Collection.class.isAssignableFrom(type);
}
}