public class JDBCUtils {

    private static DataSource druid;

    private static ThreadLocal<Connection> threadlocal = new ThreadLocal<>();

    static{

        try{

            // 为了保证程序代码的可移植性，需要基于一个基准来读取这个文件

            InputStream input = JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties");

            Properties pro = new Properties();

            pro.load(input);

            druid = DruidDataSourceFactory.createDataSource(pro);

        }catch(Exception e){

            throw new RuntimeException(e);

        }

    }

    public static Connection getConnection(){

        Connection connection = null;

        try{

            //1. 尝试从当前线程检查是否存在已经绑定的 Connection 对象

            connection = threadlocal.get();

            //2. 检查 connection 对象是否为 Null

            if(connection == null){

                //3. 如果为 null, 则从数据资源获取数据连接

                connection = druid.getConnection();

                //4. 获取到数据库连接绑定到当前线程

                threadlocal.set(connection);

            }

        }catch(Exception e){

            throw new RuntimeException(e);

        }

        return connection;

    }

    public static void releaseclose(Connection connection){

       try{

           if(connection != null){

               // 关闭连接，释放资源

               connection.close();

               p("数据库已关闭");

               // 将当前数据库连接从线程上删除

               threadlocal.remove();

           }

       }catch(Exception e){

           throw new RuntimeException(e);

       }

    }

}