@Override
  public void preScannerOpen(ObserverContext<? extends RegionCoprocessorEnvironment> c, Scan scan)
    throws IOException {
    // Add another family:qualifier
    scan.addColumn(FAMILY_TO_ADD, QUALIFIER_TO_ADD);
  }
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