Pattern matching using java streams

Question

I have implemented the logic to extract some value from a string using regex like this.

for(int i = 0; i < fragmentedHeader.length - 1; i++) {
    if(fragmentedHeader[i + 1].contains("ads_management")) {
        Pattern pattern = Pattern.compile("[0-9]{15}");
        Matcher matcher = pattern.matcher(fragmentedHeader[i]);
        while (matcher.find()) {
            catalogIds.add(matcher.group());
        }
    }
}

Its working as expected. I now have to implement this logic using java streams to make it more readable.I just wanted to make it more readable and easy to the eye. I have implement using this but its not working any suggestions.

Pattern pattern = Pattern.compile("[0-9]{15}");
catalogIds = IntStream.range(0, fragmentedHeader.length - 1)
    .filter(index -> fragmentedHeader[index+1].contains("ads_management") && pattern.matcher(fragmentedHeader[index]).find())
    .mapToObj(index -> fragmentedHeader[index])
    .collect(Collectors.toList());

catalogIds = catalogIds.stream()
    .map(header -> pattern.matcher(header).group())
    .collect(Collectors.toList());

The error I am getting is no match found. But is there any way to supply matcher to the next stream

.filter(index -> fragmentedHeader[index+1].contains("ads_management") && pattern.matcher(fragmentedHeader[index]).find())
.mapToObj(index-> pattern.matcher(fragmentedHeader[index]).group())

Answer 1

You can use the method Matcher.results() to get a stream of match results for each subsequence of the input sequence that matches the pattern. That will also enables you to do the task in one go instead of the intermadiate steps you are doing right now like storing sub-results in a list.

List<String> catalogIds =
IntStream.range(0, fragmentedHeader.length - 1)
        .filter(index -> fragmentedHeader[index+1].contains("ads_management"))
        .mapToObj(index -> fragmentedHeader[index])
        .flatMap(str -> Pattern.compile("[0-9]{15}").matcher(str).results())
        .map(MatchResult::group)
        .collect(Collectors.toList());