public Set<SystemStream> getSerdeStreams(String systemName) {
    Config subConf = subset(String.format("systems.%s.streams.", systemName), true);
    Set<SystemStream> legacySystemStreams = subConf.keySet().stream()
      .filter(k -> k.endsWith(MSG_SERDE) || k.endsWith(KEY_SERDE))
      .map(k -> {
        String streamName = k.substring(0, k.length() - 16 /* .samza.XXX.serde length */);
        return new SystemStream(systemName, streamName);
      })
      .collect(Collectors.toSet());

    Set<SystemStream> systemStreams = subset(STREAMS_PREFIX).keySet().stream()
      .filter(k -> k.endsWith(MSG_SERDE) || k.endsWith(KEY_SERDE))
      .map(k -> k.substring(0, k.length() - 16 /* .samza.XXX.serde length */))
      .filter(streamId -> systemName.equals(getSystem(streamId)))
      .map(streamId -> streamIdToSystemStream(streamId)).collect(Collectors.toSet());

    return Sets.union(legacySystemStreams, systemStreams).immutableCopy();
  }
Returns a list of all SystemStreams that have a serde defined from the config file.
samza-core/src/main/java/org/apache/samza/config/StreamConfig.java