import java.io.*;
import java.util.*;

public class stringtest {
    public static void main(String[] args) throws IOException {
        String query = "select a,b,c from xyz, username, password";

        List<String> parts = new ArrayList(Arrays.asList(query.split(",")));

        String username = parts.get(parts.size() - 1);
        parts.remove(parts.size() - 1);

        String password = parts.get(parts.size() - 1);
        parts.remove(parts.size() - 1);

        String finalQuery = String.join("+", parts);

        System.out.format("query: %s \n", finalQuery);
        System.out.format("username: %s \n", username);
        System.out.format("password: %s \n", password);
    }
}