sqlclauseset.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

/*
 * Copyright (C) 1999-2004 <A href="http://www-ist.massey.ac.nz/JBDietrich" target="_top">Jens Dietrich</a>
 *
 * 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
 */
package org.mandarax.sql;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Iterator;
import java.util.List;
import java.util.Vector;

import org.apache.commons.collections.iterators.SingletonIterator;
import org.mandarax.kernel.AbstractPropertiesSupport;
import org.mandarax.kernel.Clause;
import org.mandarax.kernel.ClauseSet;
import org.mandarax.kernel.ClauseSetChangeListener;
import org.mandarax.kernel.ClauseSetException;
import org.mandarax.kernel.Predicate;
import org.mandarax.util.logging.LogCategories;

/**
 * An SQL clause set is basically a wrapper around a ResultSet of an SQL query where each
 * row in the result set is considered as a single clause (fact).
 * @author <A href="http://www-ist.massey.ac.nz/JBDietrich" target="_top">Jens Dietrich</A>
 * @version 3.4 <7 March 05>
 * @since 1.5
 */
public class SQLClauseSet extends AbstractPropertiesSupport implements ClauseSet, LogCategories {

	private String whereClause = "";
	private SQLPredicate predicate = null;
	private String query = null;
	private List cache = null;
	private long cacheTimeout = NO_CACHE;
	private long cacheTimestamp = 0;
	public static final int NO_CACHE = -1;
	private boolean closeConnection = true;

	/**
	 * Constructor.
	 */
	public SQLClauseSet() {
		super();
	}

	/**
	 * Constructor.
	 * @p a predicate
	 */
	public SQLClauseSet(SQLPredicate p) {
		this(p, NO_CACHE);
	}

	/**
	 * Constructor.
	 * @param p a predicate
	 * @param where a where clause
	 */
	public SQLClauseSet(SQLPredicate p, String where) {
		this(p, where, NO_CACHE);
	}

	/**
	 * Constructor.
	 * @param p a predicate
	 * @param timeout  the timeout after which the cache expires, if NO_CACHE , no caching is done
	 */
	public SQLClauseSet(SQLPredicate p, long timeout) {
		this(p, "", timeout);
	}

	/**
	 * Constructor.
	 * @param p a predicate
	 * @param where a where clause
	 * @param timeout  the timeout after which the cache expires, if NO_CACHE , no caching is done
	 */
	public SQLClauseSet(SQLPredicate p, String where, long timeout) {
		super();
		predicate = p;
		whereClause = where;
		cacheTimeout = timeout;
	}

	/**
	 * Add a clause set listener.
	 * @param l the listener
	 */
	public void addClauseSetChangeListener(ClauseSetChangeListener l) {
	}

	/**
	 * Iterate over all clauses.
	 * @return a clause iterator
	 * @throws ClauseSetException
	 */
	public org.mandarax.util.ClauseIterator clauses() throws ClauseSetException {
		try {
			if (useCache()) {
				return new CachedClauseIterator(cache);
			}
			else {
				String query = getQuery();
				Connection con = predicate.getDataSource().getConnection();
				LOG_SQL.debug("Execute SQL: " + query);
				Statement stmt = con.createStatement();
				ResultSet rs = stmt.executeQuery(query);

				// next line bugfix 1.9
				if (cacheTimeout != NO_CACHE) {
					cache = new Vector();
					cacheTimestamp = System.currentTimeMillis();
				}
				return new SQLClauseIterator(predicate, rs, cache,closeConnection,con);
			}
		}
		catch (Exception x) {
			LOG_SQL.error("Exception executing SQL", x);
			throw new ClauseSetException("Exception building clause from SQL",x);
		}

	}

	/**
	 * Get an iterator for clauses. The clause passed represents a query
	 * which can be used to restrict the clause set. E.g., if the clause
	 * iterator is built from database objects, and some of the variables
	 * in the query clause are already replaced by constants, these constants
	 * might be used to form a <code>WHERE</code> clause restricting the set of database objects
	 * used to establish the clauses. The additional parameter provides a general
	 * purpose interface to pass additional information, e.g. to sort the clause
	 * set.
	 * @return a clause iterator
	 * @param query the query clause
	 * @param additionalParameter an optional additional parameter
	 * @throws ClauseSetException
	 */
	public org.mandarax.util.ClauseIterator clauses(Clause query, Object additionalParameter) throws ClauseSetException {
		return clauses();
	}

	/**
	 * Get a key for indexing. The knowledge base is supposed to
	 * contain only clauses having the same key object. This method
	 * returns this key object. Note that this behavior is not enforced!
	 * @see org.mandarax.kernel.Fact#getKey
	 * @see org.mandarax.kernel.Rule#getKey
	 * @see org.mandarax.kernel.KnowledgeBase
	 * @return the key object
	 */
	public Object getKey() {
		return predicate;
	}

	/**
	 * Get the predicate.
	 * @return a predicate
	 */
	public Predicate getPredicate() {
		return predicate;
	}

	/**
	 * Get the query build from the SELECT statement from the predicate
	 * plus the additional WHERE clause set here.
	 * @return a query
	 */
	public String getQuery() {
		if (query == null) {
			String q = predicate.getQuery().trim();
			String w = getWhereClause();
			if (w != null) {
				w = w.trim();

				if (w.length() > 0) {
					if (w.toLowerCase().indexOf("where") == 0) {
						q = q + " " + w;
					}
					else {
						q = q + " where " + w;
					}
				}
			}
			query = q;		
		}
		return query;
	}

	/**
	 * Get the where clause
	 * @return the where clause
	 */
	public String getWhereClause() {
		return whereClause;
	}

	/**
	 * Remove a clause set listener.
	 * @param l the listener
	 */
	public void removeClauseSetChangeListener(ClauseSetChangeListener l) {
	}
	/**
	 * Set a predicate.
	 * @param p a predicate
	 */
	public void setPredicate(Predicate p) {
		if (p instanceof SQLPredicate) setSQLPredicate((SQLPredicate)p);
		else throw new IllegalArgumentException("SQLClauseSets expect SQLPredicates");
	}
	/**
	 * Set an SQL predicate.
	 * @param p a predicate
	 */
	public void setSQLPredicate(SQLPredicate p) {
		predicate = p;
	}

	/**
	 * Set a WHERE clause.
	 * @param p a predicate
	 */
	public void setWhereClause(String c) {
		whereClause = c;
		query = null;
	}

	/**
	 * Indicates whether the cache can be used.
	 * @return a boolean
	 */
	private boolean useCache() {
		if (cache == null) {
			return false;
		}
		else {
			if (cacheTimeout == NO_CACHE) {
				cache = null;
				return false;
			}
			else {
				// check whether cache is expired
				if ((System.currentTimeMillis() - cacheTimestamp) > (cacheTimeout * 1000)) {
					cache = null;
					return false;
				}
				else {
					return true;
				}
			}
		}
	}
	
	/**
	 * Sets whether to close the connection at the end.
	 * @param closeConnection a boolean
	 */
	public void setCloseConnection(boolean closeConnection) {
		this.closeConnection = closeConnection;
	}

	/**
	 * Set the cache time out. The cache expires after this time.
	 * @param a timeout in milli seconds, use NO_CACHE in order to switch caching off
	 */
	public void setCacheTimeout(long timeout) {
		cacheTimeout = timeout;
	}

	/**
	 * Get the cache time out. The cache expires after this time.
	 * @return a timeout in milli seconds, NO_CACHE indicates that there is no caching
	 */
	public long getCacheTimeout() {
		return cacheTimeout;
	}

	/**
	 * Compare objects.
	 * @param obj another object
	 * @return a boolean
	 */
	public boolean equals(Object obj) {
		if ((obj != null) && (obj instanceof SQLClauseSet)) {
			SQLClauseSet c = (SQLClauseSet) obj;
			boolean result = true;

			// compare query, name and data source
			// bugfix in 1.8 - thanks to [e-mail]
			result = (predicate == null) ? (c.predicate == null) : predicate.equals(c.predicate);
			result = result && ((whereClause == null) ? (c.whereClause == null) : whereClause.equals(c.whereClause));
			result = result && ((cacheTimeout == c.cacheTimeout));
			result = result && (closeConnection==c.closeConnection);

			return result;
		}
		else {
			return false;
		}
	}

	/**
	 * Get the hashcode of the object.
	 * @return the hash code of the object
	 */
	public int hashCode() {
		return ((predicate == null) ? 0 : predicate.hashCode())
			^ ((whereClause == null) ? 0 : whereClause.hashCode());
	}
	/**
	 * Indicates whether to close the connection at the end.
	 * @return a boolean
	 */
	public boolean isCloseConnection() {
		return closeConnection;
	}
	/**
	 * Get an iterator iterating over the predicates contained in this clause set.
	 * @return an iterator
	 */
	public Iterator predicates() {
		return new SingletonIterator(predicate);
	}

}