abstractadapter.java

Mandarax是一个规则引擎的纯Java实现。它支持多类型的事实和基于反映的规则

package org.mandarax.zkb.framework;

/**
 *  Copyright (C) 1999-2004  Jens Dietrich (mailto:[e-mail])
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;

import org.jdom.Element;
import org.mandarax.kernel.ClauseSet;
import org.mandarax.kernel.Fact;
import org.mandarax.kernel.LogicFactory;
import org.mandarax.kernel.PropertiesSupport;
import org.mandarax.kernel.Rule;
import org.mandarax.kernel.Term;
import org.mandarax.sql.SQLClauseSet;
import org.mandarax.util.logging.LogCategories;
import org.mandarax.zkb.ObjectPersistencyService;
import org.mandarax.zkb.ZKBException;

/**
 * An abstract class implementing XMLAdapter. Some utility methods are implemented here.
 * @author <A href="http://www-ist.massey.ac.nz/JBDietrich" target="_top">Jens Dietrich</A>
 * @version 3.4 <7 March 05>
 * @since 2.2
 */
public abstract class AbstractAdapter
	implements Adapter, LogCategories, TagAndAttributeNames {
	protected LogicFactory lfactory = LogicFactory.getDefaultFactory();
	
	// constants for dtd generation
	public static final String ZERO_OR_ONE = "?";
	public static final String ONE_OR_MANY = "+";
	public static final String ZERO_OR_MANY = "*";
	public static final String ZONE = "*";
	/**
	 * Utility method that locates the appropriate driver and exports an object using this driver.
	 * @param obj an object
	 * @param kindOfObject the kind of object, usually a constant defined in GenericDriver
	 * @param driver the generic driver
	 * @param ops the object persistency service
	 * @return an element
	 * @exception a ZKBException is thrown if export fails
	 */
	protected Element exportObject(
		Object obj,
		String kindOfObject,
		GenericDriver driver,
		ObjectPersistencyService ops)
		throws ZKBException {
		Adapter adapter = driver.getAdapter(kindOfObject);
		return adapter.exportObject(obj, driver, ops);
	}
	/**
	 * Utility method to export an array of objects and add the elements to the parent.
	 * @param objs the objects
	 * @param parent the parent element
	 * @param kindOfObject the kind of object, usually a constant defined in GenericDriver
	 * @param driver the generic driver
	 * @param ops the object persistency service
	 * @exception a ZKBException is thrown if export fails
	 */
	protected void exportChildren(
		Object[] objs,
		Element parent,
		String kindOfObject,
		GenericDriver driver,
		ObjectPersistencyService ops)
		throws ZKBException {
		Adapter adapter = driver.getAdapter(kindOfObject);
		for (int i = 0; i < objs.length; i++) {
			Element e = adapter.exportObject(objs[i], driver, ops);
			parent.addContent(e);
		}
	}
	/**
	 * Utility method to export a collection of objects and add the elements to the parent.
	 * @param objs the objects
	 * @param parent the parent element
	 * @param kindOfObject the kind of object, usually a constant defined in GenericDriver
	 * @param driver the generic driver
	 * @param ops the object persistency service
	 * @exception an ZKBException is thrown if export fails
	 */
	protected void exportChildren(
		Collection objs,
		Element parent,
		String kindOfObject,
		GenericDriver driver,
		ObjectPersistencyService ops)
		throws ZKBException {
		Adapter adapter = driver.getAdapter(kindOfObject);
		for (Iterator it = objs.iterator(); it.hasNext();) {
			Element e = adapter.exportObject(it.next(), driver, ops);
			parent.addContent(e);
		}
	}
	/**
	 * Utility method to import a child (the first child) with a certain name (not the tag name but the symbolic name
	 * as defined in GenericDriver) of the given parent element.
	 * @param e the parent element
	 * @param name the name of the child tag
	 * @param driver the generic driver
	 * @param ops the object persistency service
	 * @param lfactory the logic factory used to create objects
	 * @return an object
	 * @exception an ZKBException is thrown if import fails
	 */
	protected Object importChild(
		Element parent,
		String name,
		GenericDriver driver,
		ObjectPersistencyService ops,
		LogicFactory lfactory)
		throws ZKBException {
		Adapter adapter = driver.getAdapter(name);
		String tagName = adapter.getTagName();
		Element child = parent.getChild(tagName);
		return adapter.importObject(child, driver, ops, lfactory);
	}
	/**
	 * Utility method to import the children with a certain name (not the tag name but the symbolic name
	 * as defined in GenericDriver) of the given parent element. The name can be null, in this case all
	 * child elements will be imported. The target type argument specifies the type of the objects
	 * in the array. Note that we return an object , not an array. But this object can be casted to
	 * an array of the target type, e.g. like in<br>
	 * <code>Term[] terms = importChildren(e,null,driver,cache,lfactory,Term.class)</code>
	 * @param e the parent element
	 * @param name the name of the child tag
	 * @param driver the generic driver
	 * @param ops the object persistency service
	 * @param lfactory the logic factory used to create objects
	 * @param targetType the expected type of elements in the array
	 * @return an object that can be casted to an array of elements of the target type
	 * @exception an ZKBException is thrown if import fails
	 */
	protected Object importChildren(
		Element parent,
		String name,
		GenericDriver driver,
		ObjectPersistencyService ops,
		LogicFactory lfactory,
		Class targetType)
		throws ZKBException {
		Adapter adapter = name == null ? null : driver.getAdapter(name);
		String tagName = name == null ? null : adapter.getTagName();
		List children =
			name == null ? parent.getChildren() : parent.getChildren(tagName);
		Object array =
			java.lang.reflect.Array.newInstance(targetType, children.size());
		for (int i = 0; i < children.size(); i++) {
			if (name == null)
				adapter =
					driver.getAdapter(((Element) children.get(i)).getName());
			Array.set(
				array,
				i,
				adapter.importObject(
					(Element) children.get(i),
					driver,
					ops,
					lfactory));
		}
		return array;
	}
	/**
	 * Utility method that checks the type of an object and throws an exception
	 * if the object is not an instance of the respective class.
	 * @param obj an object
	 * @param clazz a class
	 */
	protected void check(Object obj, Class clazz) throws ZKBException {
		if (obj == null)
			throw new ZKBException(
				"Adapter " + getClass() + " cannot export/import null");
		if (!(clazz.isAssignableFrom(obj.getClass())))
			throw new ZKBException(
				"Adapter "
					+ getClass()
					+ " cannot export/import "
					+ obj
					+ " since it does not have the following type: "
					+ clazz);
	}
	/**
	 * Assign an object id to an object and add the respective attribute to the element.
	 * Use an existing id if possible. 
	 * @param e an element 
	 * @param ops an object persistency service
	 * @param obj the object
	 */
	protected void assignURI(
		Element e,
		ObjectPersistencyService ops,
		Object obj) {
		String uri = ops.findOrBind(obj);
		e.addContent(uri);
	}
	/**
	 * Get the object with the uri found in the tag.
	 * @param e an element 
	 * @param ops the object persistency service
	 * @return an object
	 */
	protected Object getObjectByURI(Element e, ObjectPersistencyService ops) {
		String uri = e.getTextTrim();
		return ops.lookup(uri);
	}
	/**
	 * Set the type attribute.
	 * @param e an element 
	 * @param term a term
	 */
	protected void setTypeAttribute(Element e, Term t) {
		e.setAttribute(TYPE, t.getType().getName());
	}
	/**
	 * Get the class for a name, throw an ZKB exception if class cannot be loaded.
	 * @param name the name of the class
	 * @return a class
	 */
	protected Class class4Name(String name) throws ZKBException {
		try {
			return Class.forName(name);
		} catch (ClassNotFoundException x) {
			throw new ZKBException(x.getMessage());
		}
	}
	/**
	 * Print the DTD associated with this adapter on a string buffer.
	 * @param out the buffer to print on. 
	 */
	public abstract void printDTD(StringBuffer out) ;
	/**
	 * Export the properties of an object implementing PropertiesSupport. 
	 * @param parent the parent element
	 * @param ps the object implementing PropertiesSupport
	 */
	protected void exportProperties(Element parent,PropertiesSupport ps) {
		Element e = new Element(PROPERTIES);
		boolean hasProperties = false;
		for (Enumeration en = ps.propertyNames();en.hasMoreElements();) {
			String key = en.nextElement().toString();
			String value = ps.getProperty(key);
			if (value!=null) {
				Element eP = new Element(PROPERTY);
				eP.setAttribute(KEY,key);
				eP.setAttribute(VALUE,value);
				e.addContent(eP);
				hasProperties = true;
				
			}
			else LOG_ZKB.warn("Cannot export property value null for key " + key);
		}
		parent.addContent(e);
	}
	/**
	 * Import the properties of an object implementing PropertiesSupport. 
	 * @param parent the parent element
	 * @param ps the object implementing PropertiesSupport
	 */
	protected void importProperties(Element parent,PropertiesSupport ps) {
		Element e = parent.getChild(PROPERTIES);
		if (e==null) {
			if (LOG_ZKB.isDebugEnabled()) LOG_ZKB.debug("No properties tag found, cannot import properties for object " + ps);
		}
		else {
			List ePs = e.getChildren(PROPERTY);
			for (int i=0;i<ePs.size();i++) {
				Element eP = (Element)ePs.get(i);
				String key = eP.getAttributeValue(KEY); 
				String value = eP.getAttributeValue(VALUE);
				if (key!=null && value!=null) ps.setProperty(key,value);
			}
		}
	}
	/**
	 * Get the type of clause set, e.g. GenericDriver.FACT or GenericDriver.RULE.
	 * @param cs a clause set
	 * @return a string
	 */
	protected String getClauseSetType(ClauseSet cs) {
	      if (cs instanceof Rule) return RULE;
	      else if (cs instanceof Fact) return FACT;
	      else if (cs instanceof SQLClauseSet) return SQL_CLAUSE_SET;
	      else return CUSTOM_CLAUSE_SET;
	} 
	 

}