public static String getThreadIdentifier() {
    Thread currentThread = Thread.currentThread();
    return currentThread.getThreadGroup()
        + "_"
        + currentThread.getName()
        + "_"
        + currentThread.getId();
  }
Copy entire map of string collection.

<p>The copy is unmodifiable map of unmodifiable collections.

@param map string collection map
@return copy of the map or an empty map if the map is null.
core/src/main/java/feign/Util.java