Splitting A String In Java?

This looks like JSON, so the "right" answer would probably be to use a JSON parser. If this is not an option, you can remove the enclosing {}, split the string according to ", ", and then split each string according to the = sign, taking the first item:

String input = "{tchristofferson=10, mchristofferson=50}";
List<String> users =
    Arrays.stream(input.substring(1, input.length() - 1).split(", "))
          .map(s -> s.split("=")[0])
          .collect(Collectors.toList());

Here is the wrong (job security) way:

String[] usernames = str.substring(1)
                        .split("=\\d+[,}]\\s*");

Why is this the wrong way? We are throwing out the stuff we don't want. The first character (whatever it is), and hoping that "=#, " and "=#}" is the only stuff we don't want. If the string began with "{ tchristofferson=10", then the first username would get a leading space.

The better way is to match the stuff you do want. And now that I'm not trying to create the answer on an iPhone screen, here it is:

    String input = "{tchristofferson=10, mchristofferson=50}";

    Pattern USERNAME_VALUE = Pattern.compile("(\\w+)=(\\d+)");
    Matcher matcher = USERNAME_VALUE.matcher(input);

    ArrayList<String> list = new ArrayList<>();
    while(matcher.find()) {
        list.add(matcher.group(1));
    }
    String[] usernames = list.toArray(new String[0]);

This assumes each character of your usernames match the \w pattern (i.e., [a-zA-Z0-9_] and other alphanumeric Unicode code points). Modify if your username requirements are more/less restrictive.

(\w+) is used to capture the username as matcher.group(1), which is added to the list which is eventually turned into your String[].

(\d+) is also being used to capture the number associated with this user as matcher.group(2). This capture group is not (presently) being used, so you could remove the parenthesis for a small efficiency gain, i.e., "(\\w+)=\\d+". I included it in case you wanted to do something with those values as well.

If username includes numbers and special characters like = then:

String str = "tchristofferson=10,mchristofferson=50";    
Pattern ptn = Pattern.compile(",");
String[] usernames = ptn.split(str); 

You can try splitting whenever there is not (^) a word (A-Za-z):

String[] tokens = test.split("[^A-Za-z]");

And if don't mind using a List, try it like @Mureinik suggested with:

    List<String> tokens2 = Arrays.stream(test.split("[^A-Za-z]"))
            .distinct()
            .filter(w -> !w.isEmpty())
            .collect(Collectors.toList());

Edit1:

If the list contains numbers try:

String[] tokens = test.split("[^A-Za-z\w]");

I highly recommend this site if you wish to experiment with regex:

http://regexr.com/