JDBCUtils工具类

package com.dbcp;

import java.io.IOException;
import java.sql.*;
import java.util.*;

public class JDBCUtils {
    private static Properties properties;
    private static String url;
    private static String driverClass;
    private static String username;
    private static String password;
    private static Connection connection = null;
    private static PreparedStatement pstmt ;
    static {
        properties = new Properties();
        try {
            // properties.load(new FileInputStream(new File("db.properties")));
            properties.load(JDBCUtils.class.getResourceAsStream("db.properties"));
            url = properties.getProperty("url");
            driverClass = properties.getProperty("driverClass");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //得到连接
    public static Connection getConnection(){
        try {
            Class.forName(driverClass);
            connection = DriverManager.getConnection(url,username,password);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }
    //关闭所有连接
    public static void closeAll(Connection conn, Statement statement, ResultSet resultSet){

        try {
            if (resultSet!=null){
                resultSet.close();
            }
            if (conn!=null){
                conn.close();
            }
            if (statement!=null){
                statement.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    //增加，删除，修改
    public static boolean updateByPreparedStatement(String sql, List