网络通话结束时Java同步返回

Question

I have a method intercept which expects a Response object in return.

@Override
public Response intercept(Interceptor.Chain chain) throws IOException {
    Request original = chain.request();
    mRequestBuilder = original.newBuilder();

    mAgent.getToken(new OnTokenResponse() {
        @Override
        public void onSuccess(final String token) {
            mRequestBuilder.removeHeader(AUTHORIZATION);
            mRequestBuilder.header(AUTHORIZATION, "Bearer " + token);
        }

        @Override
        public void onFailure(final String error) {

        }
    });

    Request request = mRequestBuilder.build();
    return chain.proceed(request);
}

mAgent.getToken() makes a network call and returns a string in onSuccess if succeeded. Which in turn, I add as header to mRequestBuilder . Now since, the network call will take some time to finish, I want to execute Request request = mRequestBuilder.build() only after the network call is completed (either success or failure).

How can I synchronize this operation?

Answer 1

I want to execute Request request = mRequestBuilder.build() only after the network call is completed (either success or failure).

How can I synchronize this operation?

You either wait (block) until the network call completed, or you do request = mRequestBuilder.build();... in the callback itself.

Waiting/blocking is not a good idea if you do it on the main/GUI thread.

Running code inside the callback is probably not a good idea too, because the callback probably runs in some networking thread, and you definitely should not call chain.proceed() on that thread.

So the only clean way to do it is to run the network request at some appropriate point/time to obtain the result first, and only after that result is available allow the code to be called that depends on it.

I deliberately don't include an example of how to block waiting for a signal from an asynchronous callback here because you really shouldn't use this kind of blocking if it might happen to run on the GUI thread.