mysqlidgenerator.java

根据Scott W. Ambler在1998年写的关于ORM Persistence Layer的详细设计论文的设计思路,Artem Rudoy 开发了一个开源的ORM实现 -- PL(Persist

package pl.test;

import java.sql.Connection;

/**
 * ID generator for the MySql database.
 *
 * @author:
 */
public class MysqlIdGenerator
    extends AbstractHighLowIdGenerator {
    /**
     * MysqlIdGenerator constructor.
     */
    public MysqlIdGenerator() {
        super();
    }

    /**
     * Return new high value.
     *
     * @return new high value
     */
    protected long getNextHighValue(pl.map.ClassMap classMap) throws pl.
        PlException {
        Connection conn = null;
        long highValue = 1;
        java.sql.Statement st = null;
        try {
            conn = classMap.getRelationalDatabase().getConnection();
            st = conn.createStatement();
            st.execute("LOCK TABLES pl_id WRITE");
            java.sql.PreparedStatement pst = conn.prepareStatement( "SELECT last_high_value FROM pl_id");
            java.sql.ResultSet rs = pst.executeQuery();
            if (rs.next()) {
                highValue = rs.getLong(1);
                highValue++;
                java.sql.PreparedStatement tPst = conn.prepareStatement(  "UPDATE pl_id " + "SET last_high_value=?");
                tPst.setLong(1, highValue);
                tPst.executeUpdate();
                tPst.close();
            }
            else {
                java.sql.PreparedStatement tPst = conn.prepareStatement( "INSERT INTO pl_id " +  "(last_high_value) " +
                    "VALUES (?)");
                tPst.setLong(1, highValue);
                tPst.executeUpdate();
                tPst.close();
            }
            pst.close();
            st.execute("UNLOCK TABLES");
            st.close();
            rs.close();
            classMap.getRelationalDatabase().freeConnection(conn);
        }
        catch (Throwable e) {
            if (st != null) {
                try {
                    st.execute("UNLOCK TABLES");
                }
                catch (Throwable ex) {}
            }
            throw new pl.PlException(e);
        }
        highValue <<= 16;
        highValue &= 0xffffffffffff0000L;
        return highValue;
    }
}