public Set<SystemDescriptor> getSystemDescriptors() {
    return Collections.unmodifiableSet(new HashSet<>(systemDescriptors.values()));
  }
Get all the {@link SystemDescriptor}s in this application

@return an immutable set of {@link SystemDescriptor}s
samza-core/src/main/java/org/apache/samza/application/descriptors/ApplicationDescriptorImpl.java