How to return just one string from java stream

Question

I understand how to collect to a List, but can't figure how I would return just one parameter of filtered object as a String.

fee = new BigDecimal(fees
            .stream()
            .filter(p -> p.getTodate().isAfter(LocalDateTime.now()))
            .filter(p -> p.getFromdate().isBefore(LocalDateTime.now()))
            .filter(p -> p.getId().equals(id))

    return fee;

I first check that the fee is up to date, as there might be upcoming fees and fees that are no longer valid. Then I match the id with remaining fees. But then there is code missing between last filter and return.

I just want to return String from Stream object (p.getFee) for BigDecimal constructor.

I know there is only one Stream object remaining after filters.

Answer 1

Use findFirst to return the first element of the Stream that passes your filters. It returns an Optional, so you can use orElse() to set a default value in case the Stream is empty.

fee = new BigDecimal(fees
            .stream()
            .filter(p -> p.getTodate().isAfter(LocalDateTime.now()))
            .filter(p -> p.getFromdate().isBefore(LocalDateTime.now()))
            .filter(p -> p.getId().equals(id))
            .map(p -> p.getFee())
            .findFirst()
            .orElse(/*some default value*/));

Answer 2

Maybe it would be a better approach:

fee = fees.stream()
        .filter(p -> p.getTodate().isAfter(LocalDateTime.now()))
        .filter(p -> p.getFromdate().isBefore(LocalDateTime.now()))
        .filter(p -> p.getId().equals(id))
        .map(p -> p.getFee())
        .findFirst()
        .map(BigDecimal::new)
        .orElse(/*some default value*/);