JdbcKeyAuthority.java

package org.hivedb.management;

import javax.sql.DataSource;

import org.hivedb.HiveRuntimeException;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.support.incrementer.DataFieldMaxValueIncrementer;

/**
 * Persistent numeric sequence generator. JdbcKeyAuthority is a thin wrapper
 * around DataFieldMaxValueIncrementer. JdbcKeyAuthority also takes
 * responsibility for issuing CREATE statements to initialize the sequence.
 * 
 * @author Justin McCarthy (jmccarthy@cafepress.com)
 */

public class JdbcKeyAuthority implements KeyAuthority {

	DataFieldMaxValueIncrementer incrementer = null;

	private Class returnType = null;
	private Class keySpace = null;

	// Only used to issue CREATE TABLE
	private DataSource dataSource = null;

	/**
	 * @param keySpace
	 *            A class that distinguishes this counter (the class name will
	 *            be mapped to a database table)
	 * @param returnType
	 *            Type of the numeric keys this KeyAuthority generates (Integer
	 *            or Float)
	 */
	public JdbcKeyAuthority(Class keySpace, Class returnType) {
		this.keySpace = keySpace;
		this.returnType = returnType;
	}

	protected void setIncrementer(DataFieldMaxValueIncrementer incrementer) {
		this.incrementer = incrementer;
	}

	public void setDataSource(DataSource dataSource) {
		this.dataSource = dataSource;
	}

	protected DataSource getDataSource() {
		return this.dataSource;
	}

	public Object nextAvailableKey() {
		Object result = null;
		try {
			result = nextKey();
		} catch (Exception ex) {
			createSchema();
			result = nextKey();
		}
		return result;
	}

	@SuppressWarnings("unchecked")
	private Object nextKey() {
		if (Integer.class.equals(returnType))
			return new Integer(incrementer.nextIntValue());
		if (Long.class.equals(returnType))
			return new Long(incrementer.nextLongValue());
		throw new HiveRuntimeException("Unable to generate key for type "
				+ returnType.toString());
	}

	protected void createSchema() {
		JdbcTemplate template = new JdbcTemplate(dataSource);
		template.execute("CREATE TABLE " + getKeyspaceTableName() + " (" + COLUMN_NAME
				+ " int);");
		template.execute("INSERT INTO  " + getKeyspaceTableName() + " VALUES (1)");
	}

	public static String COLUMN_NAME = "current_max_id";
	
	protected String getKeyspaceTableName() {
		return tableNameForClass(keySpace);
	}

	public static String tableNameForClass(Class aClass) {
		return "key_authority_"
				+ aClass.getName().toLowerCase().replace('.', '_').replace('$',
						'_');
	}
}