Keycloak admin REST APIs - Check username

CheckUsername.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class CheckUsername {

    public static void main(String args[]) throws IOException {
       new CheckUsername().checkUsername("user1");
    }

    public Boolean checkUsername(String username) throws IOException {

        String port = "8081";
        String realm = "api";
        String server = "localhost";
        String content_type = "application/json";
        String method_type = "GET";
        String encode_type = "UTF-8";
        String bearerToken = new GetToken().getBearerToken();

        URL url = new URL("http://" + server + ":" + port + "/auth/admin/realms/" + realm + "/users?username=" + username);

        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        conn.setRequestMethod(method_type);
        conn.setRequestProperty("Content-Type", content_type);
        conn.setRequestProperty("Authorization", "Bearer " + bearerToken.trim());
        conn.setDoOutput(true);

        BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), encode_type));
        String line;
        StringBuilder result = new StringBuilder();

        while ((line = in.readLine()) != null) {
            result.append(line);
        }
        String response = result.toString();

        if(response.contentEquals("[]")){
            return false;
        }else {
            return true;
        }
    }
}