Java – return value from asynchronous rest template spring
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Java
I'm using spring to create an asynchronous rest call
@GetMapping(path = "/testingAsync") public String value() throws ExecutionException,InterruptedException,TimeoutException { AsyncRestTemplate restTemplate = new AsyncRestTemplate(); String baseUrl = "https://api.github.com/users/XXX"; HttpHeaders requestHeaders = new HttpHeaders(); requestHeaders.setAccept(Arrays.asList(MediaType.APPLICATION_JSON)); String value = ""; httpentity entity = new httpentity("parameters",requestHeaders); ListenableFuture<ResponseEntity<User>> futureEntity = restTemplate.getForEntity(baseUrl,User.class); futureEntity.addCallback(new ListenableFutureCallback<ResponseEntity<User>>() { @Override public void onSuccess(ResponseEntity<User> result) { System.out.println(result.getBody().getName()); // instead of this how can i return the value to the user ? } @Override public void onFailure(Throwable ex) { } }); return "DONE"; // instead of done i want to return value to the user comming from the rest call }
Is there any way to convert the listenablefuture to the completable future used in Java 8?
Solution
You can basically do two things
>Delete the listenablefuturecallback and return to listenablefuture > create a deferredresult and set its value in the listenablefuturecallback
Return to listenablefuture
@GetMapping(path = "/testingAsync") public ListenableFuture<ResponseEntity<User>> value() throws ExecutionException,requestHeaders); return restTemplate.getForEntity(baseUrl,User.class); }
Spring MVC will add a listenablefuturecallback itself to fill in the deferredresult, and eventually you will get a user
Use deferredresult
If you want more control over what is returned, you can use deferredresult and set the value yourself
@GetMapping(path = "/testingAsync") public DeferredResult<String> value() throws ExecutionException,requestHeaders); final DeferredResult<String> result = new DeferredResult<>(); ListenableFuture<ResponseEntity<User>> futureEntity = restTemplate.getForEntity(baseUrl,User.class); futureEntity.addCallback(new ListenableFutureCallback<ResponseEntity<User>>() { @Override public void onSuccess(ResponseEntity<User> result) { System.out.println(result.getBody().getName()); result.setResult(result.getBody().getName()); } @Override public void onFailure(Throwable ex) { result.setErrorResult(ex.getMessage()); } }); return result; }
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