databaseidgenerator.java

这是一本描述JDBC数据库的书籍

/*
 * DatabaseIDGenerator.java
 *
 * Created on June 10, 2005, 10:58 AM
 *
 * To change this template, choose Tools | Options and locate the template under
 * the Source Creation and Management node. Right-click the template and choose
 * Open. You can then make changes to the template in the Source Editor.
 */

package ch02.oid;

import java.sql.*;
import javax.sql.*;
import common.*;

/**
 *
 * @author kevin
 */
public class DatabaseIDGenerator {
    public final static long ID_PERSON = 2;
    public final static long ID_STUDENT = 21;
    public final static long ID_EMPLOYEE = 22;
    
    public synchronized static long nextPersonID(){
        return nextID(ID_PERSON);
    }
    
    public synchronized static long nextStudentID(){
        return nextID(ID_STUDENT);
    }
    
    public synchronized static long nextEmployeeID(){
        return nextID(ID_EMPLOYEE);
    }
    
    private static long nextID(long tableID){
        Connection conn = null;
        Statement  stmt = null;
        ResultSet  rs = null;
        long result = 0;
        try{
            ConnectionFactory factory = ConnectionFactory.getConnectionFactory();
            conn = factory.getConnection();
            stmt = conn.createStatement();
            String sql = "select nextval from oid_tbl where type=" + tableID;
            rs = stmt.executeQuery(sql);
            if(rs.next()){
                result = rs.getLong("nextval");
            }
            String updateSql = "update oid_tbl set nextval = nextval where type=" + tableID;
            stmt.executeUpdate(updateSql);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            DBUtils.close(rs, stmt, conn);
        }
        return result;
    }
    
}