Injecting dependency inside AbstractWebSocketHandler - spring

Question

How to inject a dependency inside a Web Socket handler:
public class WebsocketHandler extends AbstractWebSocketHandler {
#Autowired
GreetingMap greetingMap;
#Override
protected void handleTextMessage(WebSocketSession session, TextMessage message) throws IOException {
// NullPointerException here
String greeting = greetingMap.getSampleGreetings().get("hello") + " " + message.getPayload();
session.sendMessage(new TextMessage(greeting));
}
}
The code above throws NullPointerException
What could be missing here?

Answer 1

Try using dependency injection with constructor instead #Autowired:
private GreetingMap greetingMap;
public WebsocketHandler(GreetingMap greetingMap){
this.greetingMap = greetingMap
}

Answer 2

I think the problem is that SocketHanler is not a spring bean, but is created by "new" operator:
#Configuration
#EnableWebSocket
public class WebSocketsConfiguration implements WebSocketConfigurer {
#Override
public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
registry.addHandler(new SocketHandler(), "/socket")
.setAllowedOrigins("*");
}
}
What you need to do in this case, is to inject your dependency into WebSocketConfiguration and pass it manually to SocketHandler constructor:
#Configuration
#EnableWebSocket
public class WebSocketsConfiguration implements WebSocketConfigurer {
#Autowired
MyDependency myDependency;
#Override
public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
registry.addHandler(new SocketHandler(myDependency), "/socket")
.setAllowedOrigins("*");
}
}
And in the handler, you need to add constructor that receives the dependency
public class SocketHandler extends AbstractWebSocketHandler {
private MyDependency myDependency;
public SocketHandler(MyDependency myDependency) {
this.myDependency = myDependency;
}
#Override
public void handleTextMessage(WebSocketSession session, TextMessage message) {
System.out.println(String.format("Message from client: %s", message));
}
}