写一段JDBC连接的程序，并实现数据查询。

package svn;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;public class Main {public static void main(String[] args) throws Exception {// 1、加载驱动Class.forName("com.mysql.jdbc.Driver");// 2、创建数据库连接对象Connection conn = null;conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db?useUnicode=true&characterEncoding=UTF-8","root", "123456");// 3、创建数据库命令执行对象PreparedStatement psPreparedStatement = conn.prepareStatement("select * from t_user");// Statement stmtStatement=conn.createStatement();// 4、执行数据库命令ResultSet rSet = psPreparedStatement.executeQuery();//ResultSet rs=stmtStatement.executeQuery("select * from t_user");//5、处理执行结果while(rSet.next()){int id=rSet.getInt("id");String usernameString=rSet.getString("username");String passwordString=rSet.getString("password");}if(rSet!=null)rSet.close();if(psPreparedStatement!=null)psPreparedStatement.close();if(conn!=null)conn.close();}}