How to split a string, but also keep the delimiters?

Question

I have a multiline string which is delimited by a set of different delimiters:

(Text1)(DelimiterA)(Text2)(DelimiterC)(Text3)(DelimiterB)(Text4)

Answer 1

I like the idea of StringTokenizer because it is Enumerable.
But it is also obsolete, and replace by String.split which return a boring String[] (and does not includes the delimiters).

So I implemented a StringTokenizerEx which is an Iterable, and which takes a true regexp to split a string.

A true regexp means it is not a 'Character sequence' repeated to form the delimiter:
'o' will only match 'o', and split 'ooo' into three delimiter, with two empty string inside:

[o], '', [o], '', [o]

But the regexp o+ will return the expected result when splitting "aooob"

[], 'a', [ooo], 'b', []

To use this StringTokenizerEx:

final StringTokenizerEx aStringTokenizerEx = new StringTokenizerEx("boo:and:foo", "o+");
final String firstDelimiter = aStringTokenizerEx.getDelimiter();
for(String aString: aStringTokenizerEx )
{
    // uses the split String detected and memorized in 'aString'
    final nextDelimiter = aStringTokenizerEx.getDelimiter();
}

The code of this class is available at DZone Snippets.

As usual for a code-challenge response (one self-contained class with test cases included), copy-paste it (in a 'src/test' directory) and run it. Its main() method illustrates the different usages.

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Note: (late 2009 edit)

The article Final Thoughts: Java Puzzler: Splitting Hairs does a good work explaning the bizarre behavior in String.split().
Josh Bloch even commented in response to that article:

Yes, this is a pain. FWIW, it was done for a very good reason: compatibility with Perl.
The guy who did it is Mike "madbot" McCloskey, who now works with us at Google. Mike made sure that Java's regular expressions passed virtually every one of the 30K Perl regular expression tests (and ran faster).

The Google common-library Guava contains also a Splitter which is:

• simpler to use
• maintained by Google (and not by you)

So it may worth being checked out. From their initial rough documentation (pdf):

JDK has this:

String[] pieces = "foo.bar".split("\\.");

It's fine to use this if you want exactly what it does: - regular expression - result as an array - its way of handling empty pieces

Mini-puzzler: ",a,,b,".split(",") returns...

(a) "", "a", "", "b", ""
(b) null, "a", null, "b", null
(c) "a", null, "b"
(d) "a", "b"
(e) None of the above

Answer: (e) None of the above.

",a,,b,".split(",")
returns
"", "a", "", "b"

Only trailing empties are skipped! (Who knows the workaround to prevent the skipping? It's a fun one...)

In any case, our Splitter is simply more flexible: The default behavior is simplistic:

Splitter.on(',').split(" foo, ,bar, quux,")
--> [" foo", " ", "bar", " quux", ""]

If you want extra features, ask for them!

Splitter.on(',')
.trimResults()
.omitEmptyStrings()
.split(" foo, ,bar, quux,")
--> ["foo", "bar", "quux"]

Order of config methods doesn't matter -- during splitting, trimming happens before checking for empties.