获取特定字符串后的所有内容

Question

I have a String coming as "process_client_123_Tree" and "process_abc_pqr_client_123_Tree" . I want to extract everything after "process_client_" and "process_abc_pqr_client_" and store it in a String variable.

Here currentKey variable can contain either of above two strings.

String clientId = // how to use currentKey here so that I can get remaining portion in this variable

What is the right way to do this? Should I just use split here or some regex?

Answer 1

import java.util.regex.*;

class test
{
    public static void main(String args[])
    {
        Pattern pattern=Pattern.compile("^process_(client_|abc_pqr_client_)(.*)$");
        Matcher matcher = pattern.matcher("process_client_123_Tree");
        while(matcher.find())
            System.out.println("String 1 Group 2: "+matcher.group(2));
        matcher = pattern.matcher("process_abc_pqr_client_123_Tree");
        while(matcher.find())
            System.out.println("String 2 Group 2: "+matcher.group(2));

        System.out.println("Another way..");

        System.out.println("String 1 Group 2: "+"process_client_123_Tree".replace("process_client_", ""));
        System.out.println("String 2 Group 2: "+"process_abc_pqr_client_123_Tree".replace("process_abc_pqr_client_", ""));
    }
}

Output:

$ java test
String 1 Group 2: 123_Tree
String 2 Group 2: 123_Tree
Another way..
String 1 Group 2: 123_Tree
String 2 Group 2: 123_Tree

Regex breakup:

^ match start of line
process_(client_|abc_pqr_client_) match "process_" followed by "client_" or abc_pqr_client_" (captured as group 1)
(.*)$ . means any char and * means 0 or more times, so it match the rest chars in string until end ($) and captures it as group 2

Answer 2

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Matchit{

   public static void main(String []args){
      String str = "process_abc_pqr_client_123_Tree";
      Pattern p = Pattern.compile("process_abc_pqr_client_(.*)|process_client_(.*)");
      Matcher m = p.matcher("process_abc_pqr_client_123_Tree");
      if (m.find( )) {
            System.out.println("Found value: " + m.group(1) );
      }
   }
}

Gets you:

123_Tree

The parentheses in the regexp define the match groups. The pipe is a logical or. Dot means any character and star means any number. So, I create a pattern object with that regexp and then use a matcher object to get the part of the string that has been matched.

Answer 3

A regex pattern could be: "process_(?:abc_pqr_)?client_(\\\\w+)" ^{regex101 demo}

• (?:abc_pqr_)? is the optional part
• (?: opens a non capture group )? zero or one times
• \\w+ matches one or more word characters [A-Za-z0-9_]

Demo at RegexPlanet . Matches will be in group(1) / first capturing group .

---

To extend it with limit to the right, match lazily up to the right token

"process_(?:abc_pqr_)?client_(\\w+?)_trace_count"

where \\w+? matches as few as possible word characters to meet condition.