Adapted from https://github.com/maciejzaleski/JMeter-WebSocketSampler
JMeter - WebSocket Stomp Sampler
Compiled binary can be downloaded from the Releases.
You will need following libraries in the JMeter\lib\ext folder:
jetty-http-9.1.1.v20140108.jar
jetty-io-9.1.1.v20140108.jar
jetty-util-9.1.1.v20140108.jar
websocket-api-9.1.1.v20140108.jar
websocket-client-9.1.1.v20140108.jar
websocket-common-9.1.1.v20140108.jar