Javaweb数据库通用查询BaseDao

连接数据库工具类：DBUtil.java

package util;

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

/*
 * @param null:
 * jdbc连接工具类
 * @return null
 * @author liu
 * @description TODO
 * @date 2024/5/25 17:05
 */
public class DBUtil {
   
   
    private static Connection con;
    private static final String driver;
    private static String url;
    private static String username;
    private static String password;
    static{
   
   
        // 读取数据库连接配置文件  反射机制加载类下资源
        InputStream is = DBUtil.class.getClassLoader().getResourceAsStream("db.properties");
        Properties properties = new Properties();
        try {
   
   
            // 加载输入流文件内容
            properties.load(is);
            driver = properties.getProperty("driver");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password =  properties.getProperty("password");
            Class.forName(driver);
        } catch (IOException | ClassNotFoundException e) {
   
   
            throw new RuntimeException(e);
        }
    }
    // 连接方法