TransformationValueModel.java

/*
 * Copyright (c) 2007, 2015 , Oracle. All rights reserved.
 *
 * This software is the proprietary information of Oracle Corporation.
 * Use is subject to license terms.
 */
package org.eclipse.persistence.tools.workbench.uitools.app;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import org.eclipse.persistence.tools.workbench.utility.AbstractModel;
import org.eclipse.persistence.tools.workbench.utility.Transformer;
import org.eclipse.persistence.tools.workbench.utility.events.ChangeSupport;

/**
 * A <code>TransformationValueModel</code> wraps another
 * <code>ValueModel</code> and uses a <code>Transformer</code> to transform
 * the wrapped value before it is returned by <code>getValue()</code>. As an
 * alternative to building a <code>Transformer</code>, a subclass of
 * <code>TransformationValueModel</code> can override the
 * <code>transform(Object)</code> method.
 */
@SuppressWarnings("nls")
public class TransformationValueModel
    extends AbstractModel
    implements ValueModel
{
    private Transformer transformer;

    /** The wrapped  value model. */
    protected ValueModel valueHolder;

    /** A listener that allows us to synch with changes to the wrapped value holder. */
    protected PropertyChangeListener valueChangeListener;

    // ********** constructors **********

    /**
     * Construct a value model with the specified nested value model and a
     * transformer that performs no transformations at all. Use this constructor
     * if you want to override the <code>transform(Object)</code> and method
     * instead of building a <code>Transformer</code>.
     */
    public TransformationValueModel(ValueModel valueHolder) {
        this(valueHolder, NullTransformer.instance());
    }

    /**
     * Construct an value model with the specified nested value model and
     * transformer.
     */
    @SuppressWarnings("unchecked")
    public TransformationValueModel(ValueModel valueHolder,
                                    Transformer transformer) {
        super();
        this.valueHolder = (ValueModel) valueHolder;
        this.transformer = (Transformer) transformer;
    }


    // ********** initialization **********

    @Override
    protected void initialize() {
        super.initialize();
        this.valueChangeListener = this.buildValueChangeListener();
    }

    /**
     * @see oracle.toplink.workbench.utility.AbstractModel#buildDefaultChangeSupport()
     */
    @Override
    protected ChangeSupport buildDefaultChangeSupport() {
        return new ValueModelChangeSupport(this);
    }

    protected PropertyChangeListener buildValueChangeListener() {
        return new PropertyChangeListener() {
            public void propertyChange(PropertyChangeEvent e) {
                TransformationValueModel.this.valueChanged(e);
            }
            @Override
            public String toString() {
                return "value change listener";
            }
        };
    }

    // ********** extend change support **********

    /**
     * Extend to start listening to the nested model if necessary.
     * @see Model#addPropertyChangeListener(PropertyChangeListener)
     */
    @Override
    public synchronized void addPropertyChangeListener(PropertyChangeListener listener) {
        if (this.hasNoPropertyChangeListeners(VALUE)) {
            this.engageValueHolder();
        }
        super.addPropertyChangeListener(listener);
    }

    /**
     * Extend to start listening to the nested model if necessary.
     * @see Model#addPropertyChangeListener(String, PropertyChangeListener)
     */
    @Override
    public synchronized void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
        if (propertyName == VALUE && this.hasNoPropertyChangeListeners(VALUE)) {
            this.engageValueHolder();
        }
        super.addPropertyChangeListener(propertyName, listener);
    }

    /**
     * Extend to stop listening to the nested model if necessary.
     * @see Model#removePropertyChangeListener(PropertyChangeListener)
     */
    @Override
    public synchronized void removePropertyChangeListener(PropertyChangeListener listener) {
        super.removePropertyChangeListener(listener);
        if (this.hasNoPropertyChangeListeners(VALUE)) {
            this.disengageValueHolder();
        }
    }

    /**
     * Extend to stop listening to the nested model if necessary.
     * @see Model#removePropertyChangeListener(String, PropertyChangeListener)
     */
    @Override
    public synchronized void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
        super.removePropertyChangeListener(propertyName, listener);
        if (propertyName == VALUE && this.hasNoPropertyChangeListeners(VALUE)) {
            this.disengageValueHolder();
        }
    }


    // ********** behavior **********

    /**
     * Begin listening to the value holder.
     */
    protected void engageValueHolder() {
        this.valueHolder.addPropertyChangeListener(VALUE, this.valueChangeListener);
    }

    /**
     * Stop listening to the value holder.
     */
    protected void disengageValueHolder() {
        this.valueHolder.removePropertyChangeListener(VALUE, this.valueChangeListener);
    }

    /**
     * @see oracle.toplink.workbench.utility.AbstractModel#toString(StringBuffer)
     */
    @Override
    public void toString(StringBuffer writer) {
        writer.append(this.valueHolder);
    }


    // ********** ValueModel implementation **********

    /**
     * @see ValueModel#getValue()
     */
    public Object getValue() {
        // transform the object returned by the nested value model before returning it
        return this.transform(this.valueHolder.getValue());
    }


    // ********** property change support **********

    @SuppressWarnings("unchecked")
    protected void valueChanged(PropertyChangeEvent e) {
        // transform the values before propagating the change event
        Object oldValue = this.transform(e.getOldValue());
        Object newValue = this.transform(e.getNewValue());
        this.firePropertyChanged(VALUE, oldValue, newValue);
    }


    // ********** behavior **********

    /**
     * Transform the specified object and return the result.
     * This is called by #getValue().
     */
    protected Object transform(Object value) {
        return (value == null) ? null : this.transformNonNull(value);
    }

    /**
     * Transform the specified object and return the result.
     * This is called by #getValue().
     */
    protected Object transformNonNull(Object value) {
        return this.transformer.transform(value);
    }
}