CODEWITHSUNDEEP
javaspringresttemplate
Tom Load
Tom Load

Reputation: 31

When does the AsyncRestTemplate send request?

Today I did some experiments on AsyncRestTemplate. Below is a piece of sample code:

ListenableFuture<ResponseEntity<MyObject[]>> result 
                          = asyncRestTemplate.getForEntity(uri, MyObject[]);
List<MyObject> objects = Arrays.asList(result.get().getBody());

To my surprise, the request was not sent to uri in first line (i.e. after calling getForEntity) but sent after result.get() is called.

Isn't it a synchronous way of doing stuff?

Upvotes: 2

Views: 1213

Answers (2)

Shailendra
Shailendra

Reputation: 9102

The whole idea of doing async request is that either you do not want to wait for the async task to start/complete OR you want the main thread to do some other task before asking for the result from the Future instance. Internally, the AsyncRestTemplate prepares an AsyncRequest and calls executeAsync method.

AsyncClientHttpRequest request = createAsyncRequest(url, method);
            if (requestCallback != null) {
                requestCallback.doWithRequest(request);
            }
            ListenableFuture<ClientHttpResponse> responseFuture = request.executeAsync();

There are two different implementations - HttpComponentsAsyncClientHttpRequest ( which uses high performant async support provided in Apache http component library ) and SimpleBufferingAsyncClientHttpRequest (which uses facilities provided by J2SE classes). In case of HttpComponentsAsyncClientHttpRequest, internally it has a thread factory (which is not spring managed AFAIK) whereas in SimpleBufferingAsyncClientHttpRequest, there is a provision of Spring managed AsyncListenableTaskExecutor. The whole point is that in all cases there is some ExecutorService of some kind to be able to run the tasks asynchronously. Of course as is natural with these thread pools, the actual starting time of task is indeterminate and depends upon lots of factor like load, available CPU etc. and should not be relied upon.

Upvotes: 2

Kayaman
Kayaman

Reputation: 73558

When you call future.get() you're essentially turning an asynchronous operation into a synchronous one by waiting for the result.

It doesn't matter when the actual request is performed, the important thing is that since it's asynchronous, you don't need to worry about it unless/until you need the result.

The advantage is obvious when you need to perform other work before processing the result, or when you're not waiting for a result at all.

Upvotes: 0

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