java学习之联接Mysql

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.mysql.jdbc.PreparedStatement;
import com.mysql.jdbc.Statement;


public class MysqlTest {
	
	static String drivername="com.mysql.jdbc.Driver";
 static String url="jdbc:mysql://localhost:3306/expression";//指向数据源
 static String username="root";
 static String password="";
 static java.sql.Statement stmt=null;
 static ResultSet re=null;
 static Connection conn=null;
 static PreparedStatement pstm=null;
 /*
 * 构造函数进行初始化
 */
 public MysqlTest(){
 	try{
 	Class.forName(drivername);//将驱动加载到运行环境中，加载的时候，驱动会自动向DriverManager完成注册
 	System.out.println("创建驱动成功");
 	}catch(ClassNotFoundException e){
 	e.printStackTrace();
 	}
 }
 /*
 * 获取连接
 */
 public static Connection getConnection(){
 	 conn=null;
 	try{
 	conn=(Connection)DriverManager.getConnection(url, username, password);//有了驱动和连接地址后，需要使用DriverManager来获取连接
 	System.out.println("连接数据库成功！");
 	}catch(SQLException e){
 	e.printStackTrace();
 	}
 	return conn;
 }
 /**
 * 关闭连接
 * @param args
 */
 public static void free(ResultSet rs,Connection conn,java.sql.Statement stmt2){
 	if(rs!=null){
 	try {
	rs.close();
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	System.out.println("关闭ResultSet失败！");
	e.printStackTrace();
	}finally{
	if(conn!=null){
	try {
	conn.close();
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	System.out.println("关闭Connection失败！");
	e.printStackTrace();
	}finally{
	if(stmt2!=null){
	try {
	stmt2.close();
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	 System.out.println("关闭Statement失败！");
	e.printStackTrace();
	}
	}
	}
	}
	}
 	}
 }
 public static void main(String[]args){

 	MysqlTest.getConnection();
 	try {
	stmt=conn.createStatement();
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
	}
	try {
	re=stmt.executeQuery("select * from data");
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
	}
	int i=1;
	try {
	while(re.next()){
	System.out.println(i++);
	}
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
	}
	free(re,conn,stmt);
	System.out.println("OK");
 }
}