<b>hibernate中自定义主键生成器</b>[Java编程]

Hibernate(目前利用的版本是3.2)中供应了多种生成主键的方法.

但是当前的这么多种生成方法未必能满意我们的要求.

比方increment,可以在一个hibernate实例的利用上很便利的时刻,但是在集群的时刻就不行了.

再如 identity ,sequence ,native 是数据局供应的主键生成方法,常常也不是我们需求,并且在程序跨数据库方面也表现出不足.

还有基于算法的生成方法生成出来的主键基本都是字符串的.

我们目前需求一种生成方法:利用Long作为主键范例,自动增,支持集群.

那么我们需求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的配置以下:

<id name="id" type="long" column="id" >

<generator class="hibernate.IncrementGenerator" />

</id>