hlidgenerator.java

这是一本描述JDBC数据库的书籍

/*
 * HLIDGenerator.java
 *
 * Created on June 10, 2005, 11:25 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.*;
import java.util.*;

/**
 *
 * @author kevin
 */
public class HLIDGenerator {
    private static Map idMap = new HashMap();
    
    private static long personID = 1;
    private static long studentID = 1;
    private static long employeeID = 1;
    
    public static synchronized String nextPersonID(){
        String id = (String)idMap.get("PERSON");
        if(id == null){
            id = nextID();
            idMap.put("PERSON", id);
        }
        id += personID;
        personID ++;
        return id;
    }
    
    public static synchronized String nextStudentID(){
        String id = (String)idMap.get("STUDENT");
        if(id == null){
            id = nextID();
            idMap.put("STUDENT", id);
        }
        id += studentID;
        studentID ++;
        return id;
        
    }
    
    public static synchronized String nextEmployeeID(){
        String id = (String)idMap.get("EMPLOYEE");
        if(id == null){
            id = nextID();
            idMap.put("EMPLOYEE", id);
        }
        id += employeeID;
        employeeID ++;
        return id;
        
    }
   
    private static synchronized String nextID(){
        Connection conn = null;
        Statement  stmt = null;
        ResultSet  rs = null;
        String     result = null;
        try{
            ConnectionFactory factory = ConnectionFactory.getConnectionFactory();
            conn = factory.getConnection();
            stmt = conn.createStatement();
            String sql = "select nextval from oid_hl_tbl";
            rs = stmt.executeQuery(sql);
            long id = 0;
            if(rs.next()){
                id = rs.getLong("nextval");
            }
            result = String.valueOf(id);
            String updateSql = "update oid_hl_tbl set nextval = nextval + 1";
            stmt.executeUpdate(updateSql);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            DBUtils.close(rs, stmt, conn);
        }
        return result;
    }
}