String url = "jdbc:mariadb://localhost:3306/user_msa";
String user = "user";
String pwd = "user123";

try(Connection conn = DriverManager.getConnection(url, user, pwd)) {
	Statement stmt = null;
	ResultSet rs = null;

	stmt = conn.createStatement ();
	rs = stmt.executeQuery ( "select count(*) from post" );
	rs.next ();

	int cnt = rs.getInt ( "count(*)" );
	System.out.println ( cnt );

} catch (SQLException throwables) {
	throwables.printStackTrace ( );
}

public class Service{
	private final JdbcTemplate jdbcTemplate;

	public Service(DataSource datasource){
		this.jdbcTemplate = new JdbcTemplate(datasource);
	}

	public void calcCount(){

		...
		logic
		...
	}

}

public <T> T execute(ConnectionCallback<T> action) throws DataAccessException {
		Assert.notNull(action, "Callback object must not be null");

		Connection con = DataSourceUtils.getConnection(obtainDataSource());
		try {
			// Create close-suppressing Connection proxy, also preparing returned Statements.
			Connection conToUse = createConnectionProxy(con);
			return action.doInConnection(conToUse);
		}
		catch (SQLException ex) {
			// Release Connection early, to avoid potential connection pool deadlock
			// in the case when the exception translator hasn't been initialized yet.
			String sql = getSql(action);
			DataSourceUtils.releaseConnection(con, getDataSource());
			con = null;
			throw translateException("ConnectionCallback", sql, ex);
		}
		finally {
			DataSourceUtils.releaseConnection(con, getDataSource());
		}
	}

public static Connection doGetConnection(DataSource dataSource) throws SQLException {
		Assert.notNull(dataSource, "No DataSource specified");

		ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
			conHolder.requested();
			if (!conHolder.hasConnection()) {
				logger.debug("Fetching resumed JDBC Connection from DataSource");
				conHolder.setConnection(fetchConnection(dataSource));
			}
			return conHolder.getConnection();
		}
		// Else we either got no holder or an empty thread-bound holder here.

		logger.debug("Fetching JDBC Connection from DataSource");
		Connection con = fetchConnection(dataSource);

		if (TransactionSynchronizationManager.isSynchronizationActive()) {
			try {
				// Use same Connection for further JDBC actions within the transaction.
				// Thread-bound object will get removed by synchronization at transaction completion.
				ConnectionHolder holderToUse = conHolder;
				if (holderToUse == null) {
					holderToUse = new ConnectionHolder(con);
				}
				else {
					holderToUse.setConnection(con);
				}
				holderToUse.requested();
				TransactionSynchronizationManager.registerSynchronization(
						new ConnectionSynchronization(holderToUse, dataSource));
				holderToUse.setSynchronizedWithTransaction(true);
				if (holderToUse != conHolder) {
					TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
				}
			}
			catch (RuntimeException ex) {
				// Unexpected exception from external delegation call -> close Connection and rethrow.
				releaseConnection(con, dataSource);
				throw ex;
			}
		}

		return con;
	}

	private static Connection fetchConnection(DataSource dataSource) throws SQLException {
			Connection con = dataSource.getConnection();
			if (con == null) {
				throw new IllegalStateException("DataSource returned null from getConnection(): " + dataSource);
			}
			return con;
	}

public class Service{
	private DataSource datasource;

	public Service(DataSource datasource){
		this.datasource = datasource;
	}

	public void quering(){
		TransactionSynchronizationManager.initSynchromization();
		Connection conn = DataSourceUtils.getConnection(this.datasource);
		conn.setAutoCommit(false);

		try{

		} catch (Exception e) {
				conn.rollback();
		} finally{
			DataSourceUtils.releaseConnection(conn, this.datasource);
			TransactionSynchronizationManager.unbindResource(this.datasource);
			TransactionSynchronizationManager.clearSynchronization();
		}

	}

}

[1]
public interface Service{
[2]
	void method1();
}

[3]
public class ServiceImpl implements Service{
[4]
	public void method1(){

	}

}

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {

	/**
	 * Alias for {@link #transactionManager}.
	 * @see #transactionManager
	 */
	@AliasFor("transactionManager")
	String value() default "";

	@AliasFor("value")
	String transactionManager() default "";

	String[] label() default {};

	Propagation propagation() default Propagation.REQUIRED;

	Isolation isolation() default Isolation.DEFAULT;

	int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;

	String timeoutString() default "";

	boolean readOnly() default false;

	Class<? extends Throwable>[] rollbackFor() default {};

	String[] rollbackForClassName() default {};

	Class<? extends Throwable>[] noRollbackFor() default {};

	String[] noRollbackForClassName() default {};

}

public enum Propagation {
	REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),
	SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),
	MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),
	REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),
	NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),
	NEVER(TransactionDefinition.PROPAGATION_NEVER),
	NESTED(TransactionDefinition.PROPAGATION_NESTED);

	private final int value;

	Propagation(int value) {
		this.value = value;
	}

	public int value() {
		return this.value;
	}

}

public enum Isolation {

	DEFAULT(TransactionDefinition.ISOLATION_DEFAULT),
	READ_UNCOMMITTED(TransactionDefinition.ISOLATION_READ_UNCOMMITTED),
	READ_COMMITTED(TransactionDefinition.ISOLATION_READ_COMMITTED),
	REPEATABLE_READ(TransactionDefinition.ISOLATION_REPEATABLE_READ),
	SERIALIZABLE(TransactionDefinition.ISOLATION_SERIALIZABLE);

	private final int value;

	Isolation(int value) {
		this.value = value;
	}

	public int value() {
		return this.value;
	}

}