CheckedGenerics.java

public interface CheckedFunction<I, O, T extends Throwable> {
		O apply(I input) throws T;
	}

	private static <I, O, R, T extends Throwable> CheckedFunction<I, R, T> combine(CheckedFunction<I, O, T> left, CheckedFunction<O, R, T> right) {
		return input -> right.apply(left.apply(input));
	}

	public static final class DBRow {
		final String query;

		public DBRow(String query) {
			this.query = query;
		}

		public DBResult save() {
			return DBResult.SUCCESS;
		}
	}

	public enum DBResult {
		ERROR,
		SUCCESS
	}

	public static final class DBException extends Exception {
		private static final long serialVersionUID = 3046735561004119190L;
	}

	public static DBRow fetchRow(String input) throws DBException {
		if (input == null) {
			throw new DBException();
		}
		return new DBRow(input);
	}

	public static String fetchRow0(String input) {
		return input;
	}

	public static void main(String[] args) {
		CheckedFunction<String, DBResult, DBException> fetchThenSave = combine(AbstractRepoModule::fetchRow, DBRow::save);
		try {
			fetchThenSave.apply("");
		} catch (DBException e) {
			e.printStackTrace();
		}
		CheckedFunction<String, byte[], RuntimeException> combine = combine(AbstractRepoModule::fetchRow0, String::getBytes);

	}