JDBCUtil工具类回顾

package util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

import exception.DataAccessException;

public class JdbcUtil {
	private static Properties config;
	private static ThreadLocal<Connection> threadLocal;
	static{
		try {
			threadLocal=new ThreadLocal<Connection>();
			config=new Properties();
			config.load(JdbcUtil.class
								.getClassLoader()
								.getResourceAsStream("jdbc.properties"));
			Class.forName(config.getProperty("driver"));
		} catch (Exception e) {
			e.printStackTrace();
			throw new ExceptionInInitializerError("JdbcUtil初始化错误");
		} 
	}
	
	//保证一个事务一个连接，一个事务一个业务，一个事务一次操作，一个线程一个事务
	//每个线程获得一个连接
	public static Connection getConnection(){
		
		
		Connection con=threadLocal.get();
		
		if(con==null){
		
			try {
				con=DriverManager.getConnection(config.getProperty("url"),
												config.getProperty("username"),
												config.getProperty("password"));	
				threadLocal.set(con);
			} catch (Exception e) {
				e.printStackTrace();
				throw new DataAccessException("数据访问失败",e);
			}
		}
		return con;
	}
	
	public static void close(Connection con,PreparedStatement ps,ResultSet rs){
		if(rs!=null){
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		if(ps!=null){
			try {
				ps.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		if(con!=null){
			try {
				con.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	
	//关闭跟本线程相关的连接
	public static void close(){
		Connection con=threadLocal.get();
		if(con!=null){
			try {
				con.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			threadLocal.remove();
		}
	}
	
}