java - 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)

I can split this string into its parts, using String.split, but it seems that I can't get the actual string, which matched the delimiter regex.

In other words, this is what I get:

• Text1
• Text2
• Text3
• Text4

This is what I want

• Text1
• DelimiterA
• Text2
• DelimiterC
• Text3
• DelimiterB
• Text4

Is there any JDK way to split the string using a delimiter regex but also keep the delimiters?

Answer 1

You can use Lookahead and Lookbehind. Like this:

System.out.println(Arrays.toString("a;b;c;d".split("(?<=;)")));
System.out.println(Arrays.toString("a;b;c;d".split("(?=;)")));
System.out.println(Arrays.toString("a;b;c;d".split("((?<=;)|(?=;))")));

And you will get:

[a;, b;, c;, d]
[a, ;b, ;c, ;d]
[a, ;, b, ;, c, ;, d]

The last one is what you want.

((?<=;)|(?=;)) equals to select an empty character before ; or after ;.

Hope this helps.

EDIT Fabian Steeg comments on Readability is valid. Readability is always the problem for RegEx. One thing, I do to help easing this is to create a variable whose name represent what the regex does and use Java String format to help that. Like this:

static public final String WITH_DELIMITER = "((?<=%1$s)|(?=%1$s))";
...
public void someMethod() {
...
final String[] aEach = "a;b;c;d".split(String.format(WITH_DELIMITER, ";"));
...
}
...

This helps a little bit. :-D