Java中的MySQLUtils_java mysqlutil

package com.youngman.Server;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
public class MySQLUtils {
 
	public static Statement stmt = null;
	public static Connection conn = null;
 
	public static void connetDatabse() throws SQLException,
			ClassNotFoundException {
 
		Class.forName("com.mysql.jdbc.Driver");
		String url = "jdbc:mysql://localhost:3306/paoding";
		String user = "root";
		String password = "";
		if (conn != null) {
			conn.close();
			conn = null;
		}
		conn = DriverManager.getConnection(url, user, password);
		System.out.println("Connection is Successful");
		if (stmt != null) {
			stmt.close();
			stmt = null;
		}
		stmt = (Statement) conn.createStatement();
 
	}
 
	public static void closeConnet() throws SQLException {
		stmt.close();
		conn.close();
	}
 
	public static boolean isconnect() {
 
		if (stmt == null || conn == null) {
			System.out.println("MySQL Connet Fail");
			return false;
		} else {
			return true;
		}
	}
 
	public static void QueryAllData() throws SQLException {
		isconnect();
 
		String sql = "select * from userdata";
		ResultSet rs = stmt.executeQuery(sql);
		while (rs.next()) {
 
			System.out.println(rs.getInt(1) + "\t" + rs.getString("user_name")
					+ "\t" + rs.getString("password") + "\t"
					+ rs.getString("phone"));
 
		}
 
		rs.close();
 
	}
 
	public static boolean QuerySingle(String user_name) throws SQLException {
 
		String sql = "select * from userdata where user_name='" + user_name
				+ "'";
 
		return QueryUser(sql);
	}
 
	public static boolean QuerySingle(String user_name, String password)
			throws SQLException {
 
		String sql = "select * from userdata where user_name='" + user_name
				+ "' And password='" + password + "'";
		return QueryUser(sql);
	}
 
	public static boolean QueryUser(String sql) throws SQLException {
 
		isconnect();
 
		ResultSet rs = stmt.executeQuery(sql);
 
		if (rs.next()) {
			System.out.println("This user already exists");
 
			System.out.println(rs.getInt(1) + "\t" + rs.getString("user_name")
					+ "\t" + rs.getString("password") + "\t"
					+ rs.getString("phone"));
			rs.close();
			return true;
		}
		return false;
 
	}
 
}