incrementgenerator.java

介绍了hibernate的入门有一些基本常用的事例

package org.hibernate.id;

import java.io.Serializable;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.MappingException;
import org.hibernate.exception.JDBCExceptionHelper;
import org.hibernate.dialect.Dialect;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.mapping.Table;
import org.hibernate.type.Type;

/**
 * <b>increment</b><br>
 * <br>
 * An <tt>IdentifierGenerator</tt> that returns a <tt>long</tt>, constructed by
 * counting from the maximum primary key value at startup. Not safe for use in a
 * cluster!<br>
 * <br>
 * Mapping parameters supported, but not usually needed: table, column.
 *
 * @author Gavin King
 */
public class IncrementGenerator implements IdentifierGenerator, Configurable {

	private static final Log log = LogFactory.getLog(IncrementGenerator.class);

	private long next;
	private String sql;
	private Class returnClass;

	public synchronized Serializable generate(SessionImplementor session, Object object) 
	throws HibernateException {

		if (sql!=null) {
			getNext( session );
		}
		return IdentifierGeneratorFactory.createNumber(next++, returnClass);
	}

	public void configure(Type type, Properties params, Dialect d)
	throws MappingException {

		String table = params.getProperty("table");
		if (table==null) table = params.getProperty(PersistentIdentifierGenerator.TABLE);
		String column = params.getProperty("column");
		if (column==null) column = params.getProperty(PersistentIdentifierGenerator.PK);
		String schema = params.getProperty(PersistentIdentifierGenerator.SCHEMA);
        String catalog = params.getProperty(PersistentIdentifierGenerator.CATALOG);
		returnClass = type.getReturnedClass();

        sql = "select max(" + column + ") from " + Table.qualify(catalog, schema, table, d.getSchemaSeparator() );
	}

	private void getNext( SessionImplementor session ) {

		Connection conn = session.connection();
		log.debug("fetching initial value: " + sql);
		
		try {

			PreparedStatement st = conn.prepareStatement(sql);
			ResultSet rs = null;
			try {
				rs = st.executeQuery();
				if ( rs.next() ) {
					next = rs.getLong(1) + 1;
					if ( rs.wasNull() ) next = 1;
				}
				else {
					next = 1;
				}
				sql=null;
				log.debug("first free id: " + next);
			}
			finally {
				if (rs!=null) rs.close();
				st.close();
			}
			
		}
		catch (SQLException sqle) {
			throw JDBCExceptionHelper.convert(
			        session.getFactory().getSQLExceptionConverter(),
			        sqle,
			        "could not fetch initial value",
			        sql
			);
		}
	}

}