content: /*
   * Instantiator.java July 2006
   *
   * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
   *
   * 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 com.aliyun.odps.simpleframework.xml.core;
  
  import com.aliyun.odps.simpleframework.xml.strategy.Value;
  import com.aliyun.odps.simpleframework.xml.util.Cache;
  import java.lang.reflect.Constructor;
  
  import com.aliyun.odps.simpleframework.xml.util.ConcurrentCache;
  
  /**
   * The <code>Instantiator</code> 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 Instance
   */
  class InstanceFactory {
  
     /**
      * This is used to cache the constructors for the given types.
      */
     private final Cache<Constructor> cache;
     
     /**
      * Constructor for the <code>Instantiator</code> 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<Constructor>();
     }
     
     /**
      * This will create an <code>Instance</code> 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 <code>Instance</code> 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 <code>ValueInstance</code> object is used to create an object
      * by using a <code>Value</code> 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 <code>ValueInstance</code> 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 <code>getInstance</code> 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 <code>ClassInstance</code> object is used to create an object
      * by using a <code>Class</code> 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 <code>ClassInstance</code> 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 <code>getInstance</code> 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;
        }
     }
  }
  