Convert Comma Separated Values to List

Question

Assume I have a set of numbers like 1,2,3,4,5,6,7 input as a single String. I would like to convert those numbers to a List of Long objects ie List<Long>.

Can anyone recommend the easiest method?

Answer 1

You mean something like this?

String numbers = "1,2,3,4,5,6,7";

List<Long> list = new ArrayList<Long>();
for (String s : numbers.split(","))
    list.add(Long.parseLong(s));

System.out.println(list);

Since Java 8 you can rewrite it as

List<Long> list = Stream.of(numbers.split(","))
        .map(Long::parseLong)
        .collect(Collectors.toList());

---

Little shorter versions if you want to get List<String>

List<String> fixedSizeList = Arrays.asList(numbers.split(","));
List<String> resizableList = new ArrayList<>(fixedSizeList);

or one-liner

List<String> list = new ArrayList<>(Arrays.asList(numbers.split(",")));

---

Bonus info:

If your data may be in form like String data = "1, 2 , 3,4"; where comma is surrounded by some whitespaces, the split(",") will produce as result array like ["1", " 2 ", " 3", "4"].

As you see second and third element in that array contains those extra spaces: " 2 ", " 3" which would cause Long.parseLong to throw NumberFormatException (since space is not proper numerical value).

Solution here is either:

• using String#trim on those individual elements before parsing like Long.parseLong(s.trim())
• consuming those extra whitespace along , while splitting. To do that we can use split("\\s*,\\s*") where
  • \s (written as "\\s" in string literals) represents whitespace
  • * is quantifier representing zero or more so "\\s*" represents zero or more whitespaces (in other words makes it optional)

Answer 2

Simple and handy solution using java-8 (for the sake of completion of the thread):

String str = "1,2,3,4,5,6,7";
List<Long> list = Arrays.stream(str.split(",")).map(Long::parseLong).collect(Collectors.toList());

System.out.println(list);

[1, 2, 3, 4, 5, 6, 7]

Even better, using Pattern.splitAsStream():

Pattern.compile(",").splitAsStream(str).map(Long::parseLong).collect(Collectors‌​.toList());

Answer 3

String input = "1,2,3,4,5,6,7";
String[] numbers = input.split("\\,");
List<Integer> result = new ArrayList<Integer>();
for(String number : numbers) {
    try {
        result.add(Integer.parseInt(number.trim()));
    } catch(Exception e) {
        // log about conversion error
    }
}

Answer 4

You can use String.split() and Long.valueOf():

String numbers = "1,2,3,4,5,6,7";
List<Long> list = new ArrayList<Long>();
for (String s : numbers.split(","))
    list.add(Long.valueOf(s));

System.out.println(list);

Answer 5

If you're not on java8 and don't want to use loops, then you can use Guava

List<Long> longValues = Lists.transform(Arrays.asList(numbersArray.split(",")), new Function<String, Long>() {
                @Override
                public Long apply(String input) {
                    return Long.parseLong(input.trim());
                }
            });

As others have mentioned for Java8 you can use Streams.

List<Long> numbers = Arrays.asList(numbersArray.split(","))
                      .stream()
                      .map(String::trim)
                      .map(Long::parseLong)
                      .collect(Collectors.toList());

Answer 6

I've used the following recently:

import static com.google.common.collect.ImmutableList.toImmutableList;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableList;
...

    final ImmutableList<Long> result = Splitter.on(",")
        .trimResults()
        .omitEmptyStrings()
        .splitToStream(value)
        .map(Long::valueOf)
        .collect(toImmutableList());

This uses Splitter from Guava (to handle empty strings and whitespaces) and does not use the surprising String.split().

Answer 7

I would use the excellent google's Guava library to do it. String.split can cause many troubles.

String numbers="1,2,3,4,5,6,7";
Iterable<String> splitIterator = Splitter.on(',').split(numbers);
List<String> list= Lists.newArrayList(splitIterator );