public EventHandler prepare() throws Exception {
    return this;
  }
Event handlers should do all the necessary checks in this method (rather than in the
constructor, or in process()) so that the caller, which is mostly executed in the ipc context
can fail fast. Process is executed async from the client ipc, so this method gives a quick
chance to do some basic checks. Should be called after constructing the EventHandler, and
before process().
@return the instance of this class
@throws Exception when something goes wrong
hbase-server/src/main/java/org/apache/hadoop/hbase/executor/EventHandler.java