hibernate中自定义主键生成器

背景:
Hibernate(目前使用的版本是3.2)中提供了多种生成主键的方式.在下面的文章中有列出来
[hibernate]Hibernate主键生成方式 Key Generator

然而当前的这么多种生成方式未必能满足我们的要求.
比如increment,可以在一个hibernate实例的应用上很方便的时候,但是在集群的时候就不行了.
再如 identity ,sequence ,native 是数据局提供的主键生成方式,往往也不是我们需要,而且在程序跨数据库方面也体现出不足.
还有基于算法的生成方式生成出来的主键基本都是字符串的.

我们现在需要一种生成方式:使用Long作为主键类型,自动增,支持集群.
那么我们需要自定义一个我们的主键生成器才能实现了.

实现代码:

package hibernate;

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.dialect.Dialect;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.id.Configurable;
import org.hibernate.id.IdentifierGenerator;
import org.hibernate.id.PersistentIdentifierGenerator;
import org.hibernate.type.Type;


public class IncrementGenerator implements IdentifierGenerator, Configurable {
    private static final Log log = LogFactory.getLog(IncrementGenerator.class);
    private Long next;
    private String sql;
    public Serializable generate(SessionImplementor session, Object object)
            throws HibernateException {
        if (sql!=null) {
            getNext( session.connection() );
        }
       return next;

    }
    
    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);
        sql = "select max("+column +") from " + ( schema==null ? table : schema + '.' + table );
        log.info(sql);
    }
    
     private void getNext(Connection conn) throws HibernateException {
            try {
                PreparedStatement st = conn.prepareStatement(sql);
                ResultSet rs = st.executeQuery();
                if ( rs.next() ) {
                    next = rs.getLong(1) + 1;
                }
                else {
                    next = 1l;
                }
            }catch(SQLException e)
            {
                throw new HibernateException(e);
            }
            finally {
                try{
                conn.close();
                }catch(SQLException e)
                {
                    throw new HibernateException(e);
                }
            }
        }
}

配置:
在对应的hbm文件里面将id的配置如下:
       

<id name="id" type="long" column="id" >
            <generator class="hibernate.IncrementGenerator" /> 
        </id>

 

 

另一个主键生成方式的例子

package com.mc.framework.hibernate.id;

import java.io.Serializable;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.text.MessageFormat;
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.dialect.Dialect;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.id.Configurable;
import org.hibernate.id.IdentifierGeneratorFactory;
import org.hibernate.id.MultipleHiLoPerTableGenerator;
import org.hibernate.id.PersistentIdentifierGenerator;
import org.hibernate.mapping.Table;
import org.hibernate.type.Type;
import org.hibernate.util.PropertiesHelper;
import org.hibernate.util.StringHelper;

import com.htf.framework.util.ClassUtil;

public class AutoadjustMultipleHiLoGenerator
		extends MultipleHiLoPerTableGenerator 
		implements PersistentIdentifierGenerator,Configurable {

	private static final Log _log = LogFactory.getLog(AutoadjustMultipleHiLoGenerator.class);

	public static final int DEFAULT_START_VALUE = 0;
	private static final String START_VALUE = "start_value";

	public static final int DEFAULT_MAX_LO = 10000;
	protected int startValue;
	protected String _query = null;
	protected String _insert = null;
	protected String _update = null;
	protected String _tableName = null;

	protected int _maxLo;
	protected long _hi = 0;
	protected int _lo;
	protected Class<?> _returnClass;

	private String selectMaxSQL = null;

	public Serializable doWorkInCurrentTransaction(Connection conn, String sql)
			throws SQLException {

		// 这个结果是高位,保存在数据库中的值.
		int result = 0;
		int updateRows = 0;
		int nextInTable; // 表中ID的最大值

		do {
			// SQL.debug(_query);
			PreparedStatement qps = conn.prepareStatement(_query);
			PreparedStatement ips = null;
			try {
				ResultSet rs = qps.executeQuery();
				boolean isInitialized = rs.next();

				// 没有初始化,则代表ID表中,没有该表主键的记录
				if (!isInitialized) {
					nextInTable = this.getNext(conn);
					_log.debug("表中记录最大值为的下一个值 : " + nextInTable);
					int curVal = nextInTable - 1;// 当前值
					if (curVal == 0) {
						return 0;
					}

					int tmp = curVal / (_maxLo + 1);
					result = tmp + 1;

					ips = conn.prepareStatement(_insert);
					ips.setInt(1, result);
					ips.execute();
				} else {
					result = rs.getInt(1);
				}
				rs.close();
			} catch (SQLException sqle) {
				_log.error("could not read or init a hi value", sqle);
				throw sqle;
			} finally {
				if (ips != null) {
					ips.close();
				}
				qps.close();
			}

			// sql = update;
			PreparedStatement ups = conn.prepareStatement(_update);
			try {
				ups.setInt(1, result + 1);// 新值
				ups.setInt(2, result);// 旧值
				updateRows = ups.executeUpdate();
			} catch (SQLException sqle) {
				_log.error("could not update hi value in: " + _tableName, sqle);
				throw sqle;
			} finally {
				ups.close();
			}
		} while (updateRows == 0);
		return new Integer(result);
	}

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

		// 低位会不断在内存中加一,如果当低位大于 "最大的低位" 时,
		//则从数据库中将高位加一,低位归零,再一次循环
		if (_lo > _maxLo) {
			// 高位
			int hival = ((Integer) doWorkInNewTransaction(session)).intValue();
			_lo = (hival == 0) ? 1 : 0;
			_hi = hival * (_maxLo + 1);
			String msg = "高低位生成的ID的信息 : new hiValue=[{0}],maxLo=[{1}],lo=[{2}],hi=[{3}]";
			_log.debug(MessageFormat.format(msg, hival, _maxLo, _lo, _hi));
		}

		Number genedId = IdentifierGeneratorFactory.createNumber(_hi + _lo,
				_returnClass);
		_lo++;

		_log.debug("根据高低位生成的ID为: " + genedId);
		return genedId;
	}

	@Override
	public void configure(Type type, Properties params, Dialect dialect)
			throws MappingException {
		startValue = PropertiesHelper.getInt(START_VALUE, params,
				DEFAULT_START_VALUE);

		super.configure(type, params, dialect);
		_query = ClassUtil.getFieldValue(this, "query", String.class);
		_insert = ClassUtil.getFieldValue(this, "insert", String.class);
		_update = ClassUtil.getFieldValue(this, "update", String.class);
		_tableName = ClassUtil.getFieldValue(this, "tableName", String.class);

		// _maxLo = ClassUtil.getFieldValue(this, "maxLo", Integer.class);
		_maxLo = PropertiesHelper.getInt(MAX_LO, params, DEFAULT_MAX_LO);
		_lo = ClassUtil.getFieldValue(this, "lo", Integer.class);
		_returnClass = ClassUtil
				.getFieldValue(this, "returnClass", Class.class);
		configureForIncrement(type, params, dialect);
	}

	private void configureForIncrement(Type type, Properties params,
			Dialect dialect) {
		String tableList = params.getProperty("tables");

		if (tableList == null)
			tableList = params.getProperty(PersistentIdentifierGenerator.TABLES);

		String[] tables = StringHelper.split(", ", tableList);
		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);

		StringBuffer buf = new StringBuffer();
		for (int i = 0; i < tables.length; i++) {
			if (tables.length > 1) {
				buf.append("select ").append(column).append(" from ");
			}
			buf.append(Table.qualify(catalog, schema, tables[i]));
			if (i < tables.length - 1)
				buf.append(" union ");
		}
		if (tables.length > 1) {
			buf.insert(0, "( ").append(" ) ids_");
			column = "ids_." + column;
		}

		selectMaxSQL = "select max(" + column + ") from " + buf.toString();

	}

	private int getNext(Connection conn) {
		long next;
		PreparedStatement st = null;
		ResultSet rs = null;
		try {
			st = conn.prepareStatement(selectMaxSQL);
			rs = st.executeQuery();
			try {
				if (rs.next()) {
					next = rs.getLong(1) + 1;
					if (rs.wasNull())
						next = 1;
				} else {
					next = 1;
				}
				selectMaxSQL = null;
			} finally {
				if (rs != null) {
					rs.close();
				}
				if (st != null) {
					st.close();
				}
			}
		} catch (SQLException sqle) {
			throw new RuntimeException(sqle);
		}
		return new Long(next).intValue();
	}

}