How to convert the ResultSet to Stream

Java 8 provided the Stream family and easy operation of it. The way of pipeline usage made the code clear and smart.

However, ResultSet is still go with very legacy way to process. Per actual ResultSet usage, it is really helpful if converted as Stream.

	public static <T> Stream<T> queryAsStream(Connection conn, String sql, Consumer<PreparedStatement> initStatement, BiFunction<ResultSet, Long, T> mapper ) throws SQLException {
	PreparedStatement stmt = conn.prepareStatement(sql);
	if(initStatement != null) {
	initStatement.accept(stmt);
	}
	final ResultSet rs = stmt.executeQuery();
	Stream<T> stream = StreamSupport.stream(new Spliterators.AbstractSpliterator<T>(
	Long.MAX_VALUE,Spliterator.ORDERED) {
	private long index = 0;
	@Override
	public boolean tryAdvance(Consumer<? super T> action) {
	try {
	if(!rs.next()) return false;
	action.accept(mapper.apply(rs, index ++));
	} catch (SQLException e) {
	throw new RuntimeException(e.getMessage(), e);
	}
	return true;
	}
	}, false).onClose(()->DbUtil.getJDBCFunc().close(rs, stmt));
	return stream;
	}

view raw SQLExecutorHelper.java hosted with ❤ by GitHub

Here is the simple usage of above:

	// as the stream backed on Result, we must close the resource after usage.
	try(Stream<Integer> stream = SQLExecutorHelper.queryAsStream(connection
	, DbUtil.isOracle() ? GATHER_ORACLE_STATS_QUERY : GATHER_MSSQL_STATS_QUERY
	, StreamUtils.uncheckedConsumer(stmt -> stmt.setString(1, tableName))
	, StreamUtils.uncheckedBiMapper((rs, i) -> rs.getInt("NUM_ROWS")))){
	return stream.findFirst().get();
	}

view raw ImportTestUtil.java hosted with ❤ by GitHub

StreamUtils.uncheckedConsumer is required to convert the the SQLException to runtimeException to make the Lamda clear.

	@FunctionalInterface
	interface WrappedConsumer<T,E extends Throwable> {
	void accept(T t) throws E;
	}
	static <T, E extends Throwable> Consumer<T> uncheckedConsumer(WrappedConsumer<T, E> f) {
	return t -> {
	try {
	f.accept(t);
	} catch (Throwable e) {
	throw new RuntimeException(e);
	}
	};
	}

view raw StreamUtils.java hosted with ❤ by GitHub