How to Split Strings Preserving Delimiters Using Regular Expressions?

Splitting Strings with Delimiters Preserved

When working with strings that contain multiple delimiters, it becomes essential to split the string into its constituent parts while preserving the delimiter information. The String.split() method provides a straightforward mechanism for splitting strings, but it only extracts the substrings without retaining the delimiters.

To achieve the desired result of splitting a string and keeping the delimiters, one can utilize regular expressions with lookahead and lookbehind assertions. Lookahead (?=) and lookbehind (?<=) are special syntaxes that allow matching without consuming any characters from the input string.

Consider the following example:

<code class="java">String input = "(Text1)(DelimiterA)(Text2)(DelimiterC)(Text3)(DelimiterB)(Text4)";

String[] parts = input.split("((?=;)|(?<=;))");</code>

In this code:

• The regular expression (?=;) matches a position just before a semicolon (;).
• The regular expression (?<=;) matches a position just after a semicolon (;).
• The | operator specifies that the match can occur for either (?=;) or (?<=;).
• The outermost parentheses enclose the entire expression and serve as capturing parentheses.

When used with the split() method, this regular expression will identify each delimiter character (;) and create an empty match for it. Thus, the resulting array parts will contain the following elements:

[Text1, ;, Text2, ;, Text3, ;, Text4]

This approach allows us to retain the original structure of the string while dividing it into its individual components. It is a powerful technique for parsing complex strings in a way that maintains their integrity.

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