4.3. Grouping API Configuration

Configuration c = new ConfigurationBuilder().clustering().hash().groups().enabled().build();

<clustering>
  <hash>
     <groups enabled="true" />
  </hash>
</clustering>

class User {
 
   ...
   String office;
   ...
 
   int hashCode() {
      // Defines the hash for the key, normally used to determine location
      ...
   }
 
   // Override the location by specifying a group, all keys in the same
   // group end up with the same owner
   @Group
   String getOffice() {
      return office;
   }
 
}

public class KXGrouper implements Grouper<String> {
 
   // A pattern that can extract from a "kX" (e.g. k1, k2) style key
   // The pattern requires a String key, of length 2, where the first character is
   // "k" and the second character is a digit. We take that digit, and perform
   // modular arithmetic on it to assign it to group "1" or group "2".
   private static Pattern kPattern = Pattern.compile("(^k)(<a>\\d</a>)$");
 
    public String computeGroup(String key, String group) {
        Matcher matcher = kPattern.matcher(key);
        if (matcher.matches()) {
            String g = Integer.parseInt(matcher.group(2)) % 2 + "";
            return g;
        } else
            return null;
    }
 
    public Class<String> getKeyType() {
        return String.class;
    }
 
}

Configuration c = new ConfigurationBuilder().clustering().hash().groups().addGrouper(new KXGrouper()).build();

<clustering>
  <hash>
     <groups enabled="true">
        <grouper class="com.acme.KXGrouper" />
     </groups>
  </hash>
</clustering>