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Check String against list of characters and replace it dynamically – Regex

I’m trying to find a solution for this matter. I have list of characters that needs to be replaced with particular character that is mapped with the original character.

Ex : I have character map which hold the characters and it’s replacement value. Character Map :

Map<String, String> characterMap = new HashMap<String, String>();
characterMap.put("&", "x26");
characterMap.put("^", "x5e");

String that needs to be replaced : String hello = "Hello& World^"; I want replace hello string with the values in the map. This map is created from the property file and it is dynamic.

Can I achieve this by a regex ? Can I achieve this without iterating the character map ?

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Answer

You may use this code:

Map<String, String> characterMap = new HashMap<>();
characterMap.put("&", "\x26");
characterMap.put("^", "\x5e");

String hello = "Hello& World^"; 

Pattern.compile("\W").matcher(hello).replaceAll(
   m -> characterMap.getOrDefault(m.group(), m.group())
        .replaceAll("\\", "$0$0"));

Output:

"Hello\x26 World\x5e"

Details:

  • In main regex we match \W which will match any non-word
  • We extract value of each matched non-word character from characterMap or if that key is not found we get same character back.
  • We call .replaceAll("\\", "$0$0") on extracted value to get right escaping (assuming values are just using single escaping). $0 is the complete string we match in regex here which is \\ and by using $0$0 we make it \\\\.

Code Demo


Another optimized way of doing this is to construct regex using keys of your map like this:

Pattern p = Pattern.compile(characterMap.keySet().stream()
   .map(s -> Pattern.quote(s)).collect(Collectors.joining("|")));

// then use it with . getOrDefault
p.matcher(hello).replaceAll(m -> 
   characterMap.get(m.group()).replaceAll("\\", "$0$0"));
// => "Hello\x26 World\x5e"
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