Can't use "this" in stomp client subscribe - React - reactjs

Question

I have my Spring-Boot service setup so I can send messages through websocket to my browser and it works.
//#MessageMapping
#RequestMapping(value = "/notify")
#SubscribeMapping("/notification")
#SendTo("/topic/notification")
public String sendNotification() throws Exception {
sendMessage();
return "Request to update Tanks has been sent!";
}
public void sendMessage() {
this.messagingTemplate.convertAndSend("/topic/notification", "IT WORKS");
}
Here's the console log from chrome:
<<< MESSAGE
destination:/topic/notification
content-type:text/plain;charset=UTF-8
subscription:sub-1519225601109-13
message-id:f2qodiqn-8
content-length:8
IT WORKS
I want to be able to receive a message from the service and update the state in react, so, that it refetches from the backend. This is what my client looks like:
var socket = new SockJS("http://localhost:6667/refresh");
var stompClient = Stomp.over(socket);
stompClient.connect({}, function(frame) {
console.log('connected: ' + frame);
stompClient.subscribe('/topic/notification', function(notification){
console.log(notification.body);
//this.showNotification(JSON.parse(notification.body).content);
//this.showNotification(notification.body);
})
}, function(err) {
console.log('err', err);
});
And the fetch in componentDidMount()
fetch(`http://localhost:6666/front/objects`)
.then(result=>result.json())
.then(fuelTanks=>this.setState({fuelTanks}))
.catch(function(err) {
console.log('Could not fetch: ' + err.message);
}
)
I can't use this.showNotification(notification.body), hence I can't set the state to be able to refetch my objects. I tried making methods outside the class but then I can't use anything from the main class.
Is there a way to make react run componentDidMount again, or better, just access the fetch method in my class when I get a message from spring through the websocket?
Like this:
componentDidMount(){
var socket = new SockJS("http://192.168.1.139:8610/refresh");
var stompClient = Stomp.over(socket);
stompClient.connect({}, function(frame) {
console.log('connected: ' + frame);
stompClient.subscribe('/topic/notification', function(notification){
refetchTanks(); // call fetch tanks -> can't use "this"
})
}, function(err) {
console.log('err', err);
});
Thanks!

Answer 1

I know, it is a bit old question, but since it pops every time when you search for stomp issue, i thought of answering it. The way to access this in callbacks is to bind callbacks with this first, then the whole of object can be accessed in the callback.
Example:
connectCallBack(){
this.setState({loading:false})
}
errorCallback=()=>{
}
componentDidMount() {
axios.post('http://localhost:8080/subscribe', null, { params: {
deviceId
}})
.then(response => response.status)
.catch(err => console.warn(err));
const socket = new SockJS('http://localhost:8080/test');
const stompClient = Stomp.over(socket);
//stompClient.connect();
stompClient.connect( {}, this.connectCallBack, this.errorCallback);
If see above code both callbacks can access this.

Answer 2

I tried everything to be able to use my class methods and the state in stompClient's .subscribe method. I was able to connect and reconnect if the service died, nevertheless it wasn't working.
I decided to use react-stomp, which worked. I could use a class method in onMessage=.... This is what my code looks like:
<SockJsClient
url = 'http://localhost:8610/refresh/'
topics={['/topic/notification']}
onConnect={console.log("Connection established!")}
onDisconnect={console.log("Disconnected!")}
onMessage={() => this.update()} <------ this method performs a new GET
request
debug= {true}
/>
I also had to send the message in a specific way on the server side, since I was getting a JSON error when sending a string.
this.messagingTemplate.send("/topic/notification", "{"text":"text"}");
<<< MESSAGE
destination:/topic/notification
content-type:text/plain;charset=UTF-8
subscription:sub-0
message-id:aaylfxl4-1
content-length:49
{
"text": "text"
}
It currently works, but I am curious if there are other, better solutions to this issue.
EDIT: a much better solution here! Use the code from the first post and create a variable before connect to be able to access this like this var self = this;, then just access is as self.update() after subscribe!