NPE if no registered MessageConverter supporting "application/json" MIME type [SPR-11370]

[spring-projects-issues]

Anton Moiseev opened SPR-11370 and commented

If I do not register any default MessageConverter by returning false from WebSocketMessageBrokerConfigurer's configureMessageConverters() and do not provide any custom MessageConverter that supports "application/json", I get following exception:

java.lang.NullPointerException: null
	at org.springframework.messaging.simp.annotation.support.SendToMethodReturnValueHandler$SessionHeaderPostProcessor.postProcessMessage(SendToMethodReturnValueHandler.java:177)
	at org.springframework.messaging.core.AbstractMessageSendingTemplate.convertAndSend(AbstractMessageSendingTemplate.java:134)
	at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:160)
	at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:151)
	at org.springframework.messaging.simp.annotation.support.SendToMethodReturnValueHandler.handleReturnValue(SendToMethodReturnValueHandler.java:139)
	at org.springframework.messaging.handler.invocation.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:97)
	at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMatch(AbstractMethodMessageHandler.java:457)
	at org.springframework.messaging.simp.annotation.support.SimpAnnotationMethodMessageHandler.handleMatch(SimpAnnotationMethodMessageHandler.java:357)
	at org.springframework.messaging.simp.annotation.support.SimpAnnotationMethodMessageHandler.handleMatch(SimpAnnotationMethodMessageHandler.java:71)
	at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMessageInternal(AbstractMethodMessageHandler.java:409)
	at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMessage(AbstractMethodMessageHandler.java:345)
	at org.springframework.messaging.support.ExecutorSubscribableChannel$1.run(ExecutorSubscribableChannel.java:70)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)

Please, find detailed explanation by the provided Reference URL.

---

Affects: 4.0.1

Reference URL: http://stackoverflow.com/questions/21390763/how-to-specify-content-type-produced-by-a-handler-in-spring-messaging#comment32342807_21414446

[spring-projects-issues]

Rossen Stoyanchev commented

The issue is twofold. One we probably shouldn't assume a default content type if you choose not to register default converters, or at least ensure there is a converter for the default. The second issue is that if there is truly no suitable converter, it should result in a message conversion exception, not NPE.

Can you confirm if not setting the default content type, or changing to something meaningful for your case, fixes the issue? To do that you'll need to switch to the more advanced mode of configuration (remove @EnableWebSocketMessageBroker and extend directly from WebSocketMessageBrokerConfigurationSupport).

[spring-projects-issues]

Anton Moiseev commented

Confirmed. Doing the way you described and overriding getContentTypeResolver() solves the problem:

@Override
protected ContentTypeResolver getContentTypeResolver() {
    return new DefaultContentTypeResolver();
}