Flink Streaming - sser-defined data source

[Norman Spangenberg]

Hey,
In the given streaming examples the test data is always (as far as I 
understand) generated in the Flink application.
I have an application that generates test data and sends it to a 
specific port.
My question: can I specify a StreamExecutionEnvironment that listens on 
that port?
In the docs for streaming 
(https://github.com/mbalassi/incubator-flink/blob/streaming-new/docs/streaming_guide.md#basics) 
in the Kafka, Flume, ... section it is possible to listen on a specific 
port. But how can I define a custom data source on a port?

greetz norman