Java Regular Expression to Match Exact Word with Special Characters
java, regex, string
Solution
Case 2 seems the opposite as case 3, so I don't think you can combine the `Pattern`s.
For case 2, your `Pattern` could look like:
Pattern pattern = Pattern.compile("(\\s|^)Hello(\\s|$)", Pattern.CASE_INSENSITIVE);
In this case we surround the keyword by whitespace or beginning/end of input.
For case 3, your `Pattern` could look like:
Pattern pattern = Pattern.compile("[\\$#@\\^&]Hello(\\s|$)", Pattern.CASE_INSENSITIVE);
In this case, we precede the keyword with any of the special characters of your choice (note the escaped reserved characters `$` and `^`), then we accept whitespace or the end of input as the character following the keyword.
Problem
I have list of keywords entered by the user and they may contains the special characters like `$, #, @, ^, &,` etc. As per my requirement when ever i receive list of text messages i need to search for all the keywords in every message. We need to match exact keyword. CASE 1: Simple Keyword - Simple Message I used `\b` to match exact keyword and it works fine. ``` public static void main(String[] args) { String patternStr = "(?i)\\bHello\\b"; Pattern pattern = Pattern.compile(patternStr); List<String> strList = new ArrayList<String>(); strList.add("HHello Message"); strList.add("This is Hello Message "); strList.add("Now Hellos again."); for(String str : strList) { Matcher matcher = pattern.matcher(str); System.out.println(">> "+matcher.find()); } } ``` OUTPUT as Expected ``` >> false >> true >> false ``` CASE 2 : Simple Keyword - Message with Special Character Now, if i run above same code for following messages then it didn't work as expected. ``` List<String> strList = new ArrayList<String>(); strList.add("#Hello Message"); strList.add("This is Hello Message "); strList.add("Now Hellos again."); ``` OUTPUT: ``` true true false ``` Expected OUTPUT ``` false true false ``` CASE 3 : Keyword & Message with Special Character If i receive following messages and Keyword is `#Hello`. I wrote following code but it didn't work. ``` public static void main(String[] args) { String patternStr = "(?i)\\b#Hello\\b"; Pattern pattern = Pattern.compile(patternStr); List<String> strList = new ArrayList<String>(); strList.add("HHello Message"); strList.add("This is #Hello Message "); strList.add("Now Hellos again."); for(String str : strList) { Matcher matcher = pattern.matcher(str); System.out.println(">> "+matcher.find()); } } ``` OUTPUT: ``` >> false >> false >> false ``` Expected OUTPUT: ``` >> false >> true >> false ``` How can i escape the special characters and resolve` CASE 2 and CASE 3`. Please help.