Coap java-based protocol, and there are many examples, approachable.

californium-master
..................\.gitattributes
..................\.gitignore
..................\README.md
..................\about.html
..................\californium-core
..................\................\pom.xml
..................\................\src
..................\................\...\main
..................\................\...\....\java
..................\................\...\....\....\org
..................\................\...\....\....\...\eclipse
..................\................\...\....\....\...\.......\californium
..................\................\...\....\....\...\.......\...........\core
..................\................\...\....\....\...\.......\...........\....\CaliforniumFormatter.java
..................\................\...\....\....\...\.......\...........\....\CaliforniumLogger.java
..................\................\...\....\....\...\.......\...........\....\CoapClient.java
..................\................\...\....\....\...\.......\...........\....\CoapHandler.java
..................\................\...\....\....\...\.......\...........\....\CoapObserveRelation.java
..................\................\...\....\....\...\.......\...........\....\CoapResource.java
..................\................\...\....\....\...\.......\...........\....\CoapResponse.java
..................\................\...\....\....\...\.......\...........\....\CoapServer.java
..................\................\...\....\....\...\.......\...........\....\Utils.java
..................\................\...\....\....\...\.......\...........\....\WebLink.java
..................\................\...\....\....\...\.......\...........\....\coap
..................\................\...\....\....\...\.......\...........\....\....\BlockOption.java
..................\................\...\....\....\...\.......\...........\....\....\CoAP.java
..................\................\...\....\....\...\.......\...........\....\....\EmptyMessage.java
..................\................\...\....\....\...\.......\...........\....\....\LinkFormat.java
..................\................\...\....\....\...\.......\...........\....\....\MediaTypeRegistry.java
..................\................\...\....\....\...\.......\...........\....\....\Message.java
..................\................\...\....\....\...\.......\...........\....\....\MessageObserver.java
..................\................\...\....\....\...\.......\...........\....\....\MessageObserverAdapter.java
..................\................\...\....\....\...\.......\...........\....\....\Option.java
..................\................\...\....\....\...\.......\...........\....\....\OptionNumberRegistry.java
..................\................\...\....\....\...\.......\...........\....\....\OptionSet.java
..................\................\...\....\....\...\.......\...........\....\....\Request.java
..................\................\...\....\....\...\.......\...........\....\....\Response.java
..................\................\...\....\....\...\.......\...........\....\network
..................\................\...\....\....\...\.......\...........\....\.......\CoapEndpoint.java
..................\................\...\....\....\...\.......\...........\....\.......\Endpoint.java
..................\................\...\....\....\...\.......\...........\....\.......\EndpointManager.java
..................\................\...\....\....\...\.......\...........\....\.......\EndpointObserver.java
..................\................\...\....\....\...\.......\...........\....\.......\Exchange.java
..................\................\...\....\....\...\.......\...........\....\.......\ExchangeObserver.java
..................\................\...\....\....\...\.......\...........\....\.......\Matcher.java
..................\................\...\....\....\...\.......\...........\....\.......\Outbox.java
..................\................\...\....\....\...\.......\...........\....\.......\RemoteEndpoint.java
..................\................\...\....\....\...\.......\...

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