code: public static List<Class<? extends CompressionCodec>> getCodecClasses(Configuration conf) {
      String codecsString = conf.get("io.compression.codecs");
      if (codecsString != null) {
        List<Class<? extends CompressionCodec>> result
          = new ArrayList<Class<? extends CompressionCodec>>();
        StringTokenizer codecSplit = new StringTokenizer(codecsString, ",");
        while (codecSplit.hasMoreElements()) {
          String codecSubstring = codecSplit.nextToken();
          if (codecSubstring.length() != 0) {
            try {
              Class<?> cls = conf.getClassByName(codecSubstring);
              if (!CompressionCodec.class.isAssignableFrom(cls)) {
                throw new IllegalArgumentException("Class " + codecSubstring +
                                                   " is not a CompressionCodec");
              }
              result.add(cls.asSubclass(CompressionCodec.class));
            } catch (ClassNotFoundException ex) {
              throw new IllegalArgumentException("Compression codec " + 
                                                 codecSubstring + " not found.",
                                                 ex);
            }
          }
        }
        return result;
      } else {
        return null;
      }
    }
docs: Get the list of codecs listed in the configuration
  @param conf the configuration to look in
  @return a list of the Configuration classes or null if the attribute
  was not set