handle
Handles a single metadata key/value mapping. This method is called directly for singleton non repeatable) keys, but may also be called for repeated keys by the default implementation of handleRepeated. It is up to the implementation to override that method if this behaviour is unwanted.
Parameters
key
the metadata key (not necessarily a "singleton" key).
value
associated metadata value.
context
an arbitrary context object supplied to the process method.
<T>
the key/value type.