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From Niki Dokovski <nick...@gmail.com>
Subject Re: Tomcat 8 WebSocket Encoders / Decoders Questions
Date Wed, 16 Oct 2013 21:46:45 GMT
On Wed, Oct 16, 2013 at 6:36 PM, Daniel Mikusa <dmikusa@gopivotal.com>wrote:

> I have a simple WebSocket endpoint defined, it is just echoing the data
> sent by the client.  Here's the code.
>
> @ServerEndpoint(value="/websocket",
>             decoders={ListStringDecoder.class},
>             encoders={ListStringEncoder.class})
> public static class Server {
>         @OnMessage
>         public List<String> rx(List<String> in) {
>             return in;
>         }
> }
>
> As you can see by the endpoint annotation, I'm defining an encoder and
> decoder.  Here's the code for that.
>
>     public static class ListStringEncoder implements
> Encoder.Text<List<String>> {
>
>         @Override
>         public void init(EndpointConfig endpointConfig) {
>         }
>
>         @Override
>         public void destroy() {
>         }
>
>         @Override
>         public String encode(List<String> list) throws EncodeException {
>             return list.toString();
>         }
>     }
>
>     public static class ListStringDecoder implements
> Decoder.Text<List<String>> {
>
>         @Override
>         public void init(EndpointConfig endpointConfig) {
>         }
>
>         @Override
>         public void destroy() {
>         }
>
>         @Override
>         public List<String> decode(String data) throws DecodeException {
>                 List<String> tmp = new ArrayList<String>();
>                 for (String str : data.substring(1, data.length() -
> 1).split(",")) {
>                         tmp.add(str);
>                 }
>                 return tmp;
>         }
>
>         @Override
>         public boolean willDecode(String s) {
>             return s.startsWith("[") && s.endsWith("]");
>         }
>     }
>
> Now when I run this, I get the following exception as Tomcat starts up.
>
> 16-Oct-2013 11:29:40.311 SEVERE [localhost-startStop-1]
> org.apache.catalina.core.StandardContext.listenerStart Exception sending
> context initialized event to listener instance of class
> org.apache.tomcat.websocket.pojo.TesterUtil$ServerConfigListener
>  java.lang.NullPointerException
>         at
> org.apache.tomcat.websocket.Util$DecoderMatch.<init>(Util.java:428)
>         at
> org.apache.tomcat.websocket.pojo.PojoMethodMapping$MessageHandlerInfo.<init>(PojoMethodMapping.java:396)
>         at
> org.apache.tomcat.websocket.pojo.PojoMethodMapping.<init>(PojoMethodMapping.java:114)
>         at
> org.apache.tomcat.websocket.server.WsServerContainer.addEndpoint(WsServerContainer.java:194)
>         at
> org.apache.tomcat.websocket.pojo.TesterUtil$ServerConfigListener.contextInitialized(TesterUtil.java:45)
>         at
> org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4830)
>         at
> org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5276)
>         at
> org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
>         at
> org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1390)
>         at
> org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1)
>         at
> java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
>         at java.util.concurrent.FutureTask.run(FutureTask.java:166)
>         at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
>         at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
>         at java.lang.Thread.run(Thread.java:724)
>
> If I change my encoder & decoder to use "List" rather than "List<String>"
> everything works fine.
>
> Any thoughts on what's going on here?
>

Hi Dan,
IMHO current implementation of o.a.t.w.Util#getGenericType/getTypeParameter
can be improved. More detailed inspection of the typed parameter will help.
Your sample runs perfectly well on WebSocket RI implementation, hence I
think this is a bug in Tomcat.

cheers
Niki


>
> Thanks
>
> Dan
>
>
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