DomainEntityLazyLoader.java from Texai at Krugle

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/*
 * DomainEntityLazyLoader.java
 *
 * Created on March 2, 2007, 1:30 PM
 *
 * Description:
 *
 * Copyright (C) 2007 Stephen L. Reed.
 *
 * This program is free software; you can redistribute it and/or modify it under the terms
 * of the GNU General Public License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program;
 * if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package org.texai.kb.persistence.lazy;

import java.lang.reflect.Field;
import net.sf.cglib.proxy.LazyLoader;
import org.apache.log4j.Logger;
import org.texai.kb.ejb.session.DomainEntityLoaderLocal;
import org.texai.kb.persistence.DomainProperty;

/**
 *
 * @author reed
 */
public final class DomainEntityLazyLoader implements LazyLoader {
  
  /** the logger */
  private static Logger LOGGER = Logger.getLogger(DomainEntityLazyLoader.class);
  
  /** the domain entity loader */
  private final DomainEntityLoaderLocal domainEntityLoader;
  
  /** the domain instance */
  private final Object domainEntity;
  
  /** the domain instance field */
  private final Field field;
  
  /** the domain property */
  private final DomainProperty domainProperty;
  
  /** the loaded object */
  private Object loadedObject;
  
  /** the indicator that the lazy object is currently being loaded */
  private boolean isLoading = false;
  
  /** the indicator that domain entities can be loaded from the cache */
  private final boolean isLoadableFromDomainEntityCache;
  
  /**
   * Creates a new instance of DomainEntityLazyLoader.
   *
   * @param domainEntityLoader the domain entity loader
   * @param domainInstance the domain instance
   * @param field the domain instance field
   * @param domainProperty the domain property
   * @param isLoadableFromDomainEntityCache the indicator that domain entities can be loaded from the cache
   */
  public DomainEntityLazyLoader(
          final DomainEntityLoaderLocal domainEntityLoader,
          final Object domainInstance,
          final Field field,
          final DomainProperty domainProperty,
          final boolean isLoadableFromDomainEntityCache) {
    super();
    //Preconditions
    assert domainEntityLoader != null : "domainEntityLoader must not be null";
    assert domainInstance != null : "domainInstance must not be null";
    assert field != null : "field must not be null";
    assert domainProperty != null : "domainProperty must not be null";
    
    this.domainEntityLoader = domainEntityLoader;
    this.domainEntity = domainInstance;
    this.field = field;
    this.domainProperty = domainProperty;
    this.isLoadableFromDomainEntityCache = isLoadableFromDomainEntityCache;
  }
  
  /** Gets the domain entity loader.
   *
   * @return the domain entity loader
   */
  public DomainEntityLoaderLocal getDomainEntityLoader() {
    return domainEntityLoader;
  }
  
  /** Gets the domain instance.
   *
   * @return the domain instance
   */
  public Object getDomainInstance() {
    return domainEntity;
  }
  
  /** Gets the domain instance field.
   *
   * @return the domain instance field
   */
  public Field getField() {
    return field;
  }
  
  /** Gets the domain property.
   *
   * @return the domain property
   */
  public DomainProperty getDomainProperty() {
    return domainProperty;
  }
  
  /** Returns the object to which the original method invocation should be dispatched. 
   * Also replaces the lazy object with the loaded object on the domain entity so that subsequent
   * invocations will directly access the object.
   *
   * @return the object to which the original method invocation should be dispatched
   */
  public Object loadObject() throws Exception {
    if (!isLoading && loadedObject == null) {
      isLoading = true;
      loadedObject = domainEntityLoader.loadDomainEntityField(
              domainEntity,
              field,
              domainProperty,
              isLoadableFromDomainEntityCache);
      isLoading = false;
      LOGGER.debug("dynamically loaded " + loadedObject + " for field " + field);
    }
    return loadedObject;
  }
  
  /** Returns whether this lazy object is in the process of loading.
   *
   * @return whether this lazy object is in the process of loading
   */
  public boolean isLoading() {
    return isLoading();
  }
  
  /** Returns whether this lazy object is loaded.
   *
   * @return whether this lazy object is loaded
   */
  public boolean isLoaded() {
    return !isLoading && loadedObject != null;
  }
  
}
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