DB link pool

package common.db;


import java.sql.Connection;
import java.sql.Statement;

import org.apache.log4j.Logger;


/**
 * @author 
 */
public class ConnManager
{
    static Logger logger = Logger.getLogger(ConnManager.class);

    private static ConnManager instance; // 唯一实例

    private static int clients = 0;

    /**
     * 建构函数私有以防止其它对象创建本类实例
     */
    private ConnManager() {
    
    }

    /**
     * 返回唯一实例.如果是第一次调用此方法,则创建实例
     * 
     * @return ConnManager 唯一实例
     */
    public static synchronized ConnManager getInstance() {

        if(instance == null) {
            instance = new ConnManager();
            clients++;
        }
        return instance;
    }

    /**
     * 
     * @param name
     *            在属性文件中定义的连接池名字
     * @return Connection 可用连接或null
     */
    public Connection getConn(String dbName) {
    	Connection conn=null;
    	try {
    		conn= DBPool.getPool(dbName).getConnection();
		}
    	catch(Exception e) {
    		e.printStackTrace();
		}
        return conn;
    }

    /**
     * free a connection stmt: conn: a database connection
     */
    public void freeConn(Statement stmt, Connection conn,String dbName) {
        try  {
            if(stmt != null) {
                stmt.close();
            }
        }
        catch(Exception e) {
            logger.error("close Statement is failed:\n"
                    + e.getMessage());
            
            e.printStackTrace();
        }

        try {
        	if(conn!=null) {
        		conn.close();
        		logger.error("---Put connection to pool of "+dbName+" ---");
        	}
        }
        catch(Exception e) {
            logger.error(
                    "close database connention is failed:\n" + e.getMessage());
            e.printStackTrace();
        }
    }
}