hl.java

本系统是一个跨平台的搜索引擎

package com.briup;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.HashMap;
import java.util.Map;


public class HL {
	// 保存当前的high值
	private static int high;
	// 定义low值
	private static int user_id = 1;
	private static int order_id = 1;
	
	//定义一个map来存储缓存里面highlow值的使用情况,
	//("user",oid),("order",oid)
	private static Map<String, Integer> map = 
		new HashMap<String, Integer>(); 
	
	/**为user提供oid*/
	synchronized public static int nextVal_user(Connection conn){
		int id = 0;
		Integer userId = map.get("user");
		if(userId == null){
			high = base(conn,"user");
		}
		id = high + user_id;
		map.put("user", id);  
		high = map.get("user");
		//user_id++;
		return id;
	}
	
	synchronized public static int nextval_Order(Connection conn){
		return 0;
	}
	/**
	 * 读取并即时更新高值
	 * */
	synchronized public static int base(Connection conn,String user){
		String sql = 
			"select nextval from hl_tbl for update";
		Statement stmt  = null;
		ResultSet rs = null;
		try{
			stmt = conn.createStatement();
			rs = stmt.executeQuery(sql);
			while(rs.next()){
				high = rs.getInt(1);
			}
			Integer oid_user = map.get("user");
			String sqlUpdate = "";
			if(oid_user != null)
				sqlUpdate = 
					"update hl_tbl set nextval = "+ oid_user;
			else
			sqlUpdate = "update hl_tbl set nextval = "+(high + 1);
			stmt.executeUpdate(sqlUpdate);
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			DBUtil.close(rs, stmt, null);
		}
		return high;
	}
	
	public static void main(String[] ags){
		Connection conn = 
			JDBCConnectionFactory.getConnection();
		for(int i=0;i<20;i++){
			System.out.print(nextVal_user(conn)+"\t");
		}
		base(conn,"user");
		DBUtil.close(conn);
	}
}