@Override
  public void start(@SuppressWarnings("rawtypes") CoprocessorEnvironment env) throws IOException {
    RegionCoprocessorEnvironment renv = (RegionCoprocessorEnvironment) env;
    FAMILY_TO_ADD = Bytes.toBytes(renv.getConfiguration().get(FAMILY_TO_ADD_KEY));
    QUALIFIER_TO_ADD = Bytes.toBytes(renv.getConfiguration().get(QUALIFIER_TO_ADD_KEY));
  }
A RegionObserver which modifies incoming Scan requests to include additional columns than what
the user actually requested.
hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example/ScanModifyingObserver.java