reusing stream inside a stream java

January 19, 2022

Hi I just wanted to know what is wrong with my code and how can I improve it as it throws an error "stream has already been operated upon or closed" thank you here is my code:

Stream<String> stream = Files.lines(path)

stream.filter(item -> !item.contains("String")).forEach(item -> {
            Pattern pattern = Pattern.compile(REGEX);
            Matcher matcher = pattern.matcher(item);
            if (!stream.filter(items -> items.length() > 12).collect(Collectors.toList()).isEmpty() == true) {
                log.error("Item must not exceed 12 numbers {}", item);
                streamMessage.set("Items must not exceed 12 numbers");
            }
            else if(matcher.matches() == true){
                log.error("Invalid String format {}", item);
                streamMessage.set("Invalid String format");
            }
        });

I wanted to loop inside the file and check per line if the characters there exceeded 12 characters or not

>Solution :

You cannot reuse the Stream. You can create two Streams using Files.lines(path), but given your code, I don’t think it’s necessary.

You can find all the elements that are too long using a single Stream:

List<String> tooLong = 
    stream.filter(item -> !item.contains("String"))
          .filter(items -> items.length() > 12)
          .collect(Collectors.toList());

if (tooLong.size () > 0) {
    log.error("Items must not exceed 12 numbers {}", tooLong.toString ());
    streamMessage.set("Items must not exceed 12 numbers");
}