In Java how do I split a String by null char without using regex

Question

I have code of the form

 String[] splitValues = s.split("\\u0000");

that is called alot, when I did profiling I saw that each call was a regex (Pattern) to be compiled and run this was causing a significant performance impact.

I can easily compile the pattern just once but then running split still takes up significant cpu

I then looked at code for String,split() and it does optimizations if just passed a single char or backslash char but it not working for me because I specify null as \ , but I cant see how else I can do it,

public String[] split(String regex, int limit) {
        /* fastpath if the regex is a
         (1)one-char String and this character is not one of the
            RegEx's meta characters ".$|()[{^?*+\\", or
         (2)two-char String and the first char is the backslash and
            the second is not the ascii digit or ascii letter.
         */
        char ch = 0;
        if (((regex.length() == 1 &&
             ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
             (regex.length() == 2 &&
              regex.charAt(0) == '\\' &&
              (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
              ((ch-'a')|('z'-ch)) < 0 &&
              ((ch-'A')|('Z'-ch)) < 0)) &&
            (ch < Character.MIN_HIGH_SURROGATE ||
             ch > Character.MAX_LOW_SURROGATE))
        {

How can I split by null separator without need to use regular expression ?

Answer 1

The "simple" way would be to precompile the regex:

static final Pattern NULL_SEPARATOR = Pattern.compile("\\u0000");

Then just do the same as on the last line :

String[] parts = NULL_SEPARATOR.split(this, limit);

---

Or, you could add things to a List instead of building an array:

List<String> parts = new ArrayList<>();
for (int i = 0; i < input.length();) {
  int start = i;
  i = input.indexOf('\0', start);
  if (i < 0) i = input.length();

  parts.add(input.substring(start, i));

  if (i < input.length()) {
    ++i;
  }
}

Of course, this gives you a List<String> , rather than a String[] ; this may or may not work for you. This has the convenience of growing the collection for you, but you can do that yourself with a String[] too.

Depending on [profiling], you might want to consider pre-sizing the list, for example by iterating the characters looking for \\0 s as a first pass.

Answer 2

Replacing

String[] splitValues = s.split("\\u0000");

with

String[] splitValues = s.split("\0");

continues to work, but importantly allows String.split() to use its fastpath and so the split works without requiring the use of regular expressions.

What I am finding slightly confusing is why I had a \\\\ originally because doesn't that mean the \\ is treated as a literal backslash and therefore the u0000 would not be treated as unicode char ?

Answer 3

There is an Open Source java library MgntUtils that has a Utility that converts Strings to unicode sequence and vise versa:

result = "Hello World";
result = StringUnicodeEncoderDecoder.encodeStringToUnicodeSequence(result);
System.out.println(result);
result = StringUnicodeEncoderDecoder.decodeUnicodeSequenceToString(result);
System.out.println(result);

The output of this code is:

\u0048\u0065\u006c\u006c\u006f\u0020\u0057\u006f\u0072\u006c\u0064
Hello World

So what I suggest is that you can write a simple code like this

public static final String DELIMITER = StringUnicodeEncoderDecoder.decodeUnicodeSequenceToString("\\u0000");
...
String[] splitValues = s.split(DELIMITER);

This will allow you to run split() method without regex as DELIMITER will hold the null symbol as a String .
The library can be found at Maven Central or at Github It comes as maven artifact and with sources and javadoc

Here is javadoc for the class StringUnicodeEncoderDecoder