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/*
* Instantiator.java July 2006
*
* Copyright (C) 2006, Niall Gallagher
*
* Licensed 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.simpleframework.xml.core;
import java.lang.reflect.Constructor;
import org.simpleframework.xml.strategy.Value;
import org.simpleframework.xml.util.Cache;
import org.simpleframework.xml.util.ConcurrentCache;
/**
* The Instantiator is used to instantiate types that
* will leverage a constructor cache to quickly create the objects.
* This is used by the various object factories to return type
* instances that can be used by converters to create the objects
* that will later be deserialized.
*
* @author Niall Gallagher
*
* @see org.simpleframework.xml.core.Instance
*/
class InstanceFactory {
/**
* This is used to cache the constructors for the given types.
*/
private final Cache cache;
/**
* Constructor for the Instantiator object. This will
* create a constructor cache that can be used to cache all of
* the constructors instantiated for the required types.
*/
public InstanceFactory() {
this.cache = new ConcurrentCache();
}
/**
* This will create an Instance that can be used
* to instantiate objects of the specified class. This leverages
* an internal constructor cache to ensure creation is quicker.
*
* @param value this contains information on the object instance
*
* @return this will return an object for instantiating objects
*/
public Instance getInstance(Value value) {
return new ValueInstance(value);
}
/**
* This will create an Instance that can be used
* to instantiate objects of the specified class. This leverages
* an internal constructor cache to ensure creation is quicker.
*
* @param type this is the type that is to be instantiated
*
* @return this will return an object for instantiating objects
*/
public Instance getInstance(Class type) {
return new ClassInstance(type);
}
/**
* This method will instantiate an object of the provided type. If
* the object or constructor does not have public access then this
* will ensure the constructor is accessible and can be used.
*
* @param type this is used to ensure the object is accessible
*
* @return this returns an instance of the specific class type
*/
protected Object getObject(Class type) throws Exception {
Constructor method = cache.fetch(type);
if(method == null) {
method = type.getDeclaredConstructor();
if(!method.isAccessible()) {
method.setAccessible(true);
}
cache.cache(type, method);
}
return method.newInstance();
}
/**
* The ValueInstance object is used to create an object
* by using a Value instance to determine the type. If
* the provided value instance represents a reference then this will
* simply provide the value of the reference, otherwise it will
* instantiate a new object and return that.
*/
private class ValueInstance implements Instance {
/**
* This is the internal value that contains the criteria.
*/
private final Value value;
/**
* This is the type that is to be instantiated by this.
*/
private final Class type;
/**
* Constructor for the ValueInstance object. This
* is used to represent an instance that delegates to the given
* value object in order to acquire the object.
*
* @param value this is the value object that contains the data
*/
public ValueInstance(Value value) {
this.type = value.getType();
this.value = value;
}
/**
* This method is used to acquire an instance of the type that
* is defined by this object. If for some reason the type can
* not be instantiated an exception is thrown from this.
*
* @return an instance of the type this object represents
*/
public Object getInstance() throws Exception {
if(value.isReference()) {
return value.getValue();
}
Object object = getObject(type);
if(value != null) {
value.setValue(object);
}
return object;
}
/**
* This method is used acquire the value from the type and if
* possible replace the value for the type. If the value can
* not be replaced then an exception should be thrown. This
* is used to allow primitives to be inserted into a graph.
*
* @param object this is the object to insert as the value
*
* @return an instance of the type this object represents
*/
public Object setInstance(Object object) {
if(value != null) {
value.setValue(object);
}
return object;
}
/**
* This is used to determine if the type is a reference type.
* A reference type is a type that does not require any XML
* deserialization based on its annotations. Values that are
* references could be substitutes objects or existing ones.
*
* @return this returns true if the object is a reference
*/
public boolean isReference() {
return value.isReference();
}
/**
* This is the type of the object instance that will be created
* by the getInstance method. This allows the
* deserialization process to perform checks against the field.
*
* @return the type of the object that will be instantiated
*/
public Class getType() {
return type;
}
}
/**
* The ClassInstance object is used to create an object
* by using a Class to determine the type. If the given
* class can not be instantiated then this throws an exception when
* the instance is requested. For performance an instantiator is
* given as it contains a reflection cache for constructors.
*/
private class ClassInstance implements Instance {
/**
* This represents the value of the instance if it is set.
*/
private Object value;
/**
* This is the type of the instance that is to be created.
*/
private Class type;
/**
* Constructor for the ClassInstance object. This is
* used to create an instance of the specified type. If the given
* type can not be instantiated then an exception is thrown.
*
* @param type this is the type that is to be instantiated
*/
public ClassInstance(Class type) {
this.type = type;
}
/**
* This method is used to acquire an instance of the type that
* is defined by this object. If for some reason the type can
* not be instantiated an exception is thrown from this.
*
* @return an instance of the type this object represents
*/
public Object getInstance() throws Exception {
if(value == null) {
value = getObject(type);
}
return value;
}
/**
* This method is used acquire the value from the type and if
* possible replace the value for the type. If the value can
* not be replaced then an exception should be thrown. This
* is used to allow primitives to be inserted into a graph.
*
* @param value this is the value to insert as the type
*
* @return an instance of the type this object represents
*/
public Object setInstance(Object value) throws Exception {
return this.value = value;
}
/**
* This is the type of the object instance that will be created
* by the getInstance method. This allows the
* deserialization process to perform checks against the field.
*
* @return the type of the object that will be instantiated
*/
public Class getType() {
return type;
}
/**
* This is used to determine if the type is a reference type.
* A reference type is a type that does not require any XML
* deserialization based on its annotations. Values that are
* references could be substitutes objects or existing ones.
*
* @return this returns true if the object is a reference
*/
public boolean isReference() {
return false;
}
}
}