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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.opensymphony.xwork2.conversion.impl;

import com.opensymphony.xwork2.ObjectFactory;
import com.opensymphony.xwork2.conversion.NullHandler;
import com.opensymphony.xwork2.conversion.ObjectTypeDeterminer;
import com.opensymphony.xwork2.inject.Inject;
import com.opensymphony.xwork2.util.reflection.ReflectionContextState;
import com.opensymphony.xwork2.util.reflection.ReflectionProvider;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.beans.PropertyDescriptor;
import java.util.*;


/**
 * 
 * 
 * Provided that the key {@link ReflectionContextState#CREATE_NULL_OBJECTS} is in the action context with a value of true (this key is set
 * only during the execution of the {@link com.opensymphony.xwork2.interceptor.ParametersInterceptor}), OGNL expressions
 * that have caused a NullPointerException will be temporarily stopped for evaluation while the system automatically
 * tries to solve the null references by automatically creating the object.
 * 
 *
 * The following rules are used when handling null references:
 *
 * 
 * If the property is declared exactly as a {@link Collection} or {@link List}, then an ArrayList shall be
 * returned and assigned to the null references.
 * If the property is declared as a {@link Map}, then a HashMap will be returned and assigned to the null
 * references.
 * If the null property is a simple bean with a no-arg constructor, it will simply be created using the {@link
 * ObjectFactory#buildBean(java.lang.Class, java.util.Map)} method.
 * 
 *
 * 
 *
 * 
 * 
 * For example, if a form element has a text field named person.name and the expression person evaluates
 * to null, then this class will be invoked. Because the person expression evaluates to a Person class, a
 * new Person is created and assigned to the null reference. Finally, the name is set on that object and the overall
 * effect is that the system automatically created a Person object for you, set it by calling setUsers() and then
 * finally called getUsers().setName() as you would typically expect.
 * 
 * 
 *
 * @author Matt Ho
 * @author Patrick Lightbody
 */
public class InstantiatingNullHandler implements NullHandler {

    private static final Logger LOG = LogManager.getLogger(InstantiatingNullHandler.class);

    private ReflectionProvider reflectionProvider;
    private ObjectFactory objectFactory;
    private ObjectTypeDeterminer objectTypeDeterminer;

    @Inject
    public void setObjectTypeDeterminer(ObjectTypeDeterminer det) {
        this.objectTypeDeterminer = det;
    }

    @Inject
    public void setReflectionProvider(ReflectionProvider prov) {
        this.reflectionProvider = prov;
    }

    @Inject
    public void setObjectFactory(ObjectFactory fac) {
        this.objectFactory = fac;
    }

    public Object nullMethodResult(Map context, Object target, String methodName, Object[] args) {
        LOG.debug("Entering nullMethodResult");
        return null;
    }

    public Object nullPropertyValue(Map context, Object target, Object property) {
        LOG.debug("Entering nullPropertyValue [target={}, property={}]", target, property);
        boolean c = ReflectionContextState.isCreatingNullObjects(context);

        if (!c) {
            return null;
        }

        if ((target == null) || (property == null)) {
            return null;
        }

        try {
            String propName = property.toString();
            Object realTarget = reflectionProvider.getRealTarget(propName, context, target);
            Class clazz = null;

            if (realTarget != null) {
                PropertyDescriptor pd = reflectionProvider.getPropertyDescriptor(realTarget.getClass(), propName);
                if (pd == null) {
                    return null;
                }

                clazz = pd.getPropertyType();
            }

            if (clazz == null) {
                // can't do much here!
                return null;
            }

            Object param = createObject(clazz, realTarget, propName, context);

            reflectionProvider.setValue(propName, context, realTarget, param);

            return param;
        } catch (Exception e) {
            LOG.error("Could not create and/or set value back on to object", e);
        }

        return null;
    }

    private Object createObject(Class clazz, Object target, String property, Map context) throws Exception {
        if (Set.class.isAssignableFrom(clazz)) {
            return new HashSet();
        } else if (Collection.class.isAssignableFrom(clazz)) {
            return new ArrayList();
        } else if (clazz == Map.class) {
            return new HashMap();
        } else if (clazz == EnumMap.class) {
            Class keyClass = objectTypeDeterminer.getKeyClass(target.getClass(), property);
            return new EnumMap(keyClass);
        }

        return objectFactory.buildBean(clazz, context);
    }
}