private static ClassLoader getClassLoaderForCodec() {
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    if (cl == null) {
      cl = Compression.class.getClassLoader();
    }
    if (cl == null) {
      cl = ClassLoader.getSystemClassLoader();
    }
    if (cl == null) {
      throw new RuntimeException("A ClassLoader to load the Codec could not be determined");
    }
    return cl;
  }
Returns the classloader to load the Codec class from.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/compress/Compression.java