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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 lite.beans;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.HashMap;

import lite.beans.util.BeansUtils;

/**
 * Default PersistenceDelegate for normal classes. The instances of this class
 * are used when other customized PersistenceDelegate is not set in the encoders
 * for a particular type.
 * 

 * This PersistenceDelegate assumes that the bean to be made persistent has a
 * default constructor that takes no parameters or a constructor that takes some
 * properties as its parameters. Only the properties that can be got or set
 * based on the knowledge gained through an introspection will be made
 * persistent. In the case that a bean is constructed with some properties, the
 * value of these properties should be available via the conventional getter
 * method.
 * 

 * 
 * @see Encoder
 */

public class DefaultPersistenceDelegate extends PersistenceDelegate {

    // shared empty property name array
    private static String[] EMPTY_PROPERTIES = new String[0];

    // names of the properties accepted by the bean's constructor
    private String[] propertyNames = EMPTY_PROPERTIES;

    /**
     * Constructs a DefaultPersistenceDelegate instance that
     * supports the persistence of a bean which has a default constructor.
     * 
     */
    public DefaultPersistenceDelegate() {
        // empty
    }

    /**
     * Constructs a DefaultPersistenceDelegate instance that
     * supports the persistence of a bean which is constructed with some
     * properties.
     * 
     * @param propertyNames
     *            the name of the properties that are taken as parameters by the
     *            bean's constructor
     */
    public DefaultPersistenceDelegate(String[] propertyNames) {
        if (null != propertyNames) {
            this.propertyNames = propertyNames;
        }
    }

    /**
     * Initializes the new instance in the new environment so that it becomes
     * equivalent with the old one, meanwhile recording this process in the
     * encoder.
     * 

     * This is done by inspecting each property of the bean. The property value
     * from the old bean instance and the value from the new bean instance are
     * both retrieved and examined to see whether the latter mutates to the
     * former, and if not, issue a call to the write method to set the
     * equivalent value for the new instance. Exceptions occured during this
     * process are reported to the exception listener of the encoder.
     * 

     * 
     * @param type
     *            the type of the bean
     * @param oldInstance
     *            the original bean object to be recorded
     * @param newInstance
     *            the simmulating new bean object to be initialized
     * @param enc
     *            the encoder to write the outputs to
     */
    @Override
    protected void initialize(Class type, Object oldInstance,
            Object newInstance, Encoder enc) {
        // Call the initialization of the super type
        super.initialize(type, oldInstance, newInstance, enc);
        // Continue only if initializing the "current" type
        if (type != oldInstance.getClass()) {
            return;
        }

        // Get all bean properties
        BeanInfo info = null;
        try {
            info = Introspector.getBeanInfo(type);
        } catch (IntrospectionException ex) {
            enc.getExceptionListener().exceptionThrown(ex);
            return;
        }
        PropertyDescriptor[] pds = info.getPropertyDescriptors();
        Method getter, setter;
        // Initialize each found non-transient property
        for (int i = 0; i < pds.length; i++) {
            // Skip a property whose transient attribute is true
            if (Boolean.TRUE.equals(pds[i].getValue("transient"))) { //$NON-NLS-1$
                continue;
            }
            getter = pds[i].getReadMethod();
            setter = pds[i].getWriteMethod();
            // Skip a property having no setter or getter
            if (getter == null || setter == null) {
                continue;
            }

            // Get the value of the property in the old instance
            Expression getterExp = new Expression(oldInstance,
                    getter.getName(), null);
            try {
                // Calculate the old value of the property
                Object oldVal = getterExp.getValue();
                // Write the getter expression to the encoder
                enc.writeExpression(getterExp);
                // Get the target value that exists in the new environment
                Object targetVal = enc.get(oldVal);
                Object newVal = new Expression(newInstance, getter.getName(),
                        null).getValue();
                if (targetVal == null ? (newVal != null && oldVal == null)
                        : targetVal != newVal && !targetVal.equals(newVal)) {
                    enc.writeStatement(new Statement(oldInstance, setter
                            .getName(), new Object[] { oldVal }));
                }
            } catch (Exception ex) {
                enc.getExceptionListener().exceptionThrown(ex);
            }
        }
    }

    /*
     * Get the field value of an object using privileged code.
     */
    private Object getFieldValue(Object oldInstance, String fieldName)
            throws NoSuchFieldException, IllegalAccessException {
        Class c = oldInstance.getClass();
        final Field f = c.getDeclaredField(fieldName);
        AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                f.setAccessible(true);
                return null;
            }
        });
        return f.get(oldInstance);
    }

    /*
     * Get the value for the specified property of the given bean instance.
     */
    private Object getPropertyValue(
            HashMap proDscMap, Object oldInstance,
            String propName) throws Exception {
        // Try to get the read method for the property
        Method getter = null;
        if (null != proDscMap) {
            PropertyDescriptor pd = proDscMap.get(Introspector
                    .decapitalize(propName));
            if (null != pd) {
                getter = pd.getReadMethod();
            }
        }

        // Invoke read method to get the value if found
        if (null != getter) {
            return getter.invoke(oldInstance, (Object[]) null);
        }

        // Otherwise, try to access the field directly
        try {
            return getFieldValue(oldInstance, propName);
        } catch (Exception ex) {
            // Fail, throw an exception
            throw new NoSuchMethodException(
                    "The getter method for the property " //$NON-NLS-1$
                            + propName + " can't be found."); //$NON-NLS-1$
        }
    }

    /**
     * Returns an expression that represents a call to the bean's constructor.
     * The constructor may take zero or more parameters, as specified when this
     * DefaultPersistenceDelegate is constructed.
     * 
     * @param oldInstance
     *            the old instance
     * @param enc
     *            the encoder that wants to record the old instance
     * @return an expression for instantiating an object of the same type as the
     *         old instance
     */
    @Override
    protected Expression instantiate(Object oldInstance, Encoder enc) {
        Object[] args = null;

        // Set the constructor arguments if any property names exist
        if (this.propertyNames.length > 0) {
            // Prepare the property descriptors for finding getter method later
            BeanInfo info = null;
            HashMap proDscMap = null;
            try {
                info = Introspector.getBeanInfo(oldInstance.getClass(),
                        Introspector.IGNORE_ALL_BEANINFO);
                proDscMap = internalAsMap(info.getPropertyDescriptors());
            } catch (IntrospectionException ex) {
                enc.getExceptionListener().exceptionThrown(ex);
                throw new Error(ex);
            }

            // Get the arguments values
            args = new Object[this.propertyNames.length];
            for (int i = 0; i < this.propertyNames.length; i++) {
                String propertyName = propertyNames[i];
                if (null == propertyName || 0 == propertyName.length()) {
                    continue;
                }

                // Get the value for each property of the given instance
                try {
                    args[i] = getPropertyValue(proDscMap, oldInstance,
                            this.propertyNames[i]);
                } catch (Exception ex) {
                    enc.getExceptionListener().exceptionThrown(ex);
                }
            }
        }

        return new Expression(oldInstance, oldInstance.getClass(),
                BeansUtils.NEW, args);
    }

    private static HashMap internalAsMap(
            PropertyDescriptor[] propertyDescs) {
        HashMap map = new HashMap();
        for (int i = 0; i < propertyDescs.length; i++) {
            map.put(propertyDescs[i].getName(), propertyDescs[i]);
        }
        return map;
    }

    /**
     * Determines whether one object mutates to the other object. If this
     * DefaultPersistenceDelegate is constructed with one or more
     * property names, and the class of o1 overrides the
     * "equals(Object)" method, then o2 is considered to mutate to
     * o1 if o1 equals to o2. Otherwise,
     * the result is the same as the definition in
     * PersistenceDelegate.
     * 
     * @param o1
     *            one object
     * @param o2
     *            the other object
     * @return true if second object mutates to the first object, otherwise
     *         false
     */
    @Override
    protected boolean mutatesTo(Object o1, Object o2) {
        if (this.propertyNames.length > 0) {
            if (BeansUtils.declaredEquals(o1.getClass())) {
                return o1.equals(o2);
            }
        }
        return super.mutatesTo(o1, o2);
    }
}    

    

    

            

    

            



    
    






    
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