Best Practices for Developing Applications

Scanning Over Tables with Byte Array Keys

In the CDAP Java API, Bytes.stopKeyForPrefix() is a very handy tool when performing scans over tables with byte array (byte[]) keys.

The method returns a given prefix, incremented by one, in a form that is suitable for prefix matching. Here is an example, showing stopKeyForPrefix being used to generate, from a provided index key, an incremented stop key:

// Returns first that matches
@Nullable
public <T> T get(Key id, Class<T> classOfT) {
  try {
    Scanner scan = table.scan(id.getKey(), Bytes.stopKeyForPrefix(id.getKey()));
    Row row = scan.next();
    if (row == null || row.isEmpty()) {
      return null;
    }

    byte[] value = row.get(COLUMN);
    if (value == null) {
      return null;
    }

    return deserialize(value, classOfT);
  } catch (Exception e) {
    throw Throwables.propagate(e);
  }
}