Develop Reference

method in the class returns null instead of a string retrieved via async call

Utils.java
/**
* Created by faiz on 15/08/17.
*/
package com.example.android.whereabouts;
import android.util.Log;
import java.io.IOException;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public class Utils {
private String apiresponse;
private OkHttpClient okHttpClient;
public Utils(String url){
okHttpClient = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
okHttpClient.newCall(request).enqueue(new Callback() {
#Override
public void onFailure(Call call, IOException e) {
Log.e("exception",e.toString());
}
#Override
public void onResponse(Call call, okhttp3.Response response) throws IOException {
apiresponse = response.body().string();
Log.e("onResponse",apiresponse);
}
});
}
public String getData(){
if(apiresponse != null)
return apiresponse ;
else
return "error";
}
}
When i instantiate this class in my main activity and try to Log return value of getData method, it logs "error" instead of the value of variable apiresponse .
Its obvious that that it takes some time to get response from the server and getData call gets executed before the server returns a response.
So how to make sure getData gets called after onResponse has been executed.

Instead of getting a callback in Utility, You can implement that in your Activity so that call back will come to ur activity and you can update in UI without any issue.
public Utils(String url, Callback callback){
okHttpClient = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
okHttpClient.newCall(request).enqueue(callback);
}
in your actvity, you can call like,
public void getdata() {
new Utils("[url]", new Callback() {
#Override
public void onFailure(Call call, IOException e) {
Log.e("exception",e.toString());
}
#Override
public void onResponse(Call call, okhttp3.Response response) throws IOException {
apiresponse = response.body().string();
Log.e("onResponse",apiresponse);
// here you can show in UI.
}
})
}
or you can create a separate custom interface and you can do same after getting the response from the server.

You can implement a callback mechanism and call the callback method from inside the onResponse(Call call, okhttp3.Response response) method.
Here is an example. You should define this in the Utils class -
public interface Callback {
void getData(String data);
}
private Callback callback;
In the constructor pass in the activity reference when you instantiate the Utils class.
// In the activity
utilsInstance = new Utils(url, this);
// In your Utils class
public Utils(String url, Callback activityCallback) {
callback = activityCallback
}
In your activity, you need to implement this interface -
public class RetrofitActivity implements Utils.Callback {
#Override
public void getData(String data) {
// do stuff
}
}
And in your OnResponse() method, you'll call this method like so -
#Override
public void onResponse(Call call, okhttp3.Response response) throws IOException {
apiresponse = response.body().string();
callback.getData(apiresponse);
Log.e("onResponse",apiresponse);
}

I found two workarounds which I'll share here and I request the people who answered this question to share their thoughts on this.(I appreciate the answers shared on this question..thanks to you all )
Note: Its more of a "clean code question" than "how to get this thing to work question"
Solution 1:
We can wait till the onResponse method gets called in getData() like this
while(true)
if(apiresponse!=null)
return(apiresponse);
to make sure this is not an indefinite while loop we set the variable apiresponse to something in both onResponse and OnFailure methods(either one will surely get executed) to break the loop.
this one seems to work but its pretty naive to me to use infinite loop and break it.
Solution 2:
Writing an AsyncTask and the Executing Utils class in the doInBackground method of that async task.
(I think the second approach makes sense as it falls under standard practices of android so it makes the thing work and also satisfies the best practices).
Another thing: an obvious question to some would be that when you're ready to write the whole async task inside the activity, then why is it an issue to write the Utils.java code directly inside the activity. My response to that is , despite of writing the asynctask in the activity, its better because it saves me from manually handling Handlers to create another thread inside onResponse to update the UI and it also falls under standard practices . So I think this approach makes more sense overall.

Step 1 : In Utils method pass calling activity as below
public Utils(CallingActivity activity , String url)
{
Request request = new Request.Builder().url(url).build();
okHttpClient.newCall(request).enqueue(activity);
}
Step 2 : Implement Callback of OkHttpClient in your calling activity.
Step 3 : Override onFailure() and onResponse() of OkHttpClient and call Utils(this,url) in calling activity.

Spring - Retry request if service returns 409 HTTP Code

I have an Spring + CXF application which consumes a Transmission API: Transmission RPC running in another server.
According to Transmission docs, you need to send a token which is generated on the first request. The server then responds with a 409 http code along with a header containing the token. This token should be sent on all subsequent calls:
2.3.1. CSRF Protection Most Transmission RPC servers require a X-Transmission-Session-Id header to be sent with requests, to prevent
CSRF attacks. When your request has the wrong id -- such as when you
send your first request, or when the server expires the CSRF token --
the Transmission RPC server will return an HTTP 409 error with the
right X-Transmission-Session-Id in its own headers. So, the correct
way to handle a 409 response is to update your
X-Transmission-Session-Id and to resend the previous request.
I was looking for solution either using a CXF filter or interceptor, that basically will handle the 409 response and retry the initial request adding the token header. I'm thinking that clients can persist this token and send it in future calls.
I'm not very familiar with cxf so I was wondering if this can be accomplish and how. Any hint would be helpful.
Thanks!

Here spring-retry can be utilized which is now an independent project and no longer part of spring-batch.
As explained here retry callback will help make another call updated with the token header.
Pseudo code / logic in this case would look something like below
RetryTemplate template = new RetryTemplate();
Foo foo = template.execute(new RetryCallback<Foo>() {
public Foo doWithRetry(RetryContext context) {
/*
* 1. Check if RetryContext contains the token via hasAttribute. If available set the header else proceed
* 2. Call the transmission API
* 3.a. If API responds with 409, read the token
* 3.a.1. Store the token in RetryContext via setAttribute method
* 3.a.2. Throw a custom exception so that retry kicks in
* 3.b. If API response is non 409 handle according to business logic
* 4. Return result
*/
}
});
Make sure to configure the RetryTemplate with reasonable retry & backoff policies so as to avoid any resource contention / surprises.
Let know in comments in case of any queries / roadblock.
N.B.: RetryContext's implementation RetryContextSupport has the hasAttribute & setAttribute method inherited from Spring core AttributeAccessor

Assuming you are using Apache CXF JAX RS Client it is easy to do by just creating a custom Runtime Exception and ResponseExceptionMapper for it. So the idea is to manually convert 409 outcomes to some exception and then handle them correctly (in your case retry the service call).
See following code snipped for fully working example.
#SpringBootApplication
#EnableJaxRsProxyClient
public class SpringBootClientApplication {
// This can e stored somewhere in db or elsewhere
private static String lastToken = "";
public static void main(String[] args) {
SpringApplication.run(SpringBootClientApplication.class, args);
}
#Bean
CommandLineRunner initWebClientRunner(final TransmissionService service) {
return new CommandLineRunner() {
#Override
public void run(String... runArgs) throws Exception {
try {
System.out.println(service.sayHello(1, lastToken));
// catch the TokenExpiredException get the new token and retry
} catch (TokenExpiredException ex) {
lastToken = ex.getNewToken();
System.out.println(service.sayHello(1, lastToken));
}
}
};
}
public static class TokenExpiredException extends RuntimeException {
private String newToken;
public TokenExpiredException(String token) {
newToken = token;
}
public String getNewToken() {
return newToken;
}
}
/**
* This is where the magic is done !!!!
*/
#Provider
public static class TokenExpiredExceptionMapper implements ResponseExceptionMapper<TokenExpiredException> {
#Override
public TokenExpiredException fromResponse(Response r) {
if (r.getStatus() == 409) {
return new TokenExpiredException(r.getHeaderString("X-Transmission-Session-Id"));
}
return null;
}
}
#Path("/post")
public interface TransmissionService {
#GET
#Path("/{a}")
#Produces(MediaType.APPLICATION_JSON_VALUE)
String sayHello(#PathParam("a") Integer a, #HeaderParam("X-Transmission-Session-Id") String sessionId)
throws TokenExpiredException;
}
}

How to send response before actions in spring mvc

Say that my spring controller function receives a large amount of data.
I want to return 200 OK, given that the data is structured right, and after that I want to perform the processing, which might take a while.
To my understanding the only way to send response is by return command. But I don't want to end the function on response send.
Are there other ways to send response to client at the middle of the function?
Creating a new thread run is obvious but other languages (JS) let you handle it more elegantly.
#RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method = RequestMethod.POST)
public ResponseEntity<String> doSomething(#RequestBody List<Message> messages) {
HttpStatus code = (messages!=null && !messages.isEmpty()) ? HttpStatus.OK
: HttpStatus.NOT_FOUND;
return new ResponseEntity<String>(res, code);
// how do I add code here??
}

You can of course do processing after sending the response. The more general way would be to use the afterCompletion method of a HandlerInterceptor. By construction, it will be executed after the response have been sent to client, but it forces you to split you logic in 2 components the before part in controller, and the after part in the interceptor.
The alternative way is to forget Spring MVC machinery and manually commit the response in the controller:
#RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method = RequestMethod.POST)
public void doSomething(#RequestBody List<Message> messages, HttpServletResponse response) {
int code = (messages!=null && !messages.isEmpty()) ? HttpServletResponse.SC_OK
: HttpServletResponse.SC_NOT_FOUND;
if (code != HttpServletResponse.SC_OK) {
response.sendError(code, res);
return;
}
java.io.PrintWriter wr = response.getWriter();
response.setStatus(code);
wr.print(res);
wr.flush();
wr.close();
// Now it it time to do the long processing
...
}
Note the void return code to notify Spring that the response have been committed in the controller.
As a side advantage, the processing still occurs in the same thread, so you have full access to session scoped attributes or any other thread local variables used by Spring MVC or Spring Security...

You can use #Async
#RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method =
RequestMethod.POST)
public ResponseEntity<String> doSomething(#RequestBody List<Message>
messages) {
do();
HttpStatus code = (messages!=null && !messages.isEmpty()) ? HttpStatus.OK
: HttpStatus.NOT_FOUND;
return new ResponseEntity<String>(res, code);
}
#Async
void do(){
//your code
}
this work in java 8

I guess you mau use the async mechanism of spring
Async methods have been introduced in servlet 3.0 and Spring offers some support to them
Basically... you make a request; the request is handled by the server and then, in background, a new thread manages the requesta data
Here a useful link (at least i hope :) ) http://spring.io/blog/2012/05/10/spring-mvc-3-2-preview-making-a-controller-method-asynchronous/

You should use the HandlerInterceptor. But the code get a little bit more complex than expected. So, here's a code suggestion to make it simpler by putting the whole solution in a single class:
#RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method = RequestMethod.POST)
public ResponseEntity<String> doSomething(#RequestBody List<Message> messages) {
HttpStatus code = (messages!=null && !messages.isEmpty()) ? HttpStatus.OK
: HttpStatus.NOT_FOUND;
result.set(res); // Save the object to be used after response
return new ResponseEntity<String>(res, code);
}
private static final ThreadLocal<String> result = new ThreadLocal<String>();
#Bean
public HandlerInterceptor interceptor() {
return new HandlerInterceptor() {
#Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
// Get the saved object and clean for the next request
String res = result.get();
result.set(null);
// TODO Your code to be executed after response.
}
};
}

how to commit or flush the rest response in the middle of process

I'm new to both java and jersey. Now I want to use the jersey to realize a REST services with extra processing after sending the response (specifically, sleep a fix amount of seconds and then fire a different REST request in the same servlet context, so it's unlike a REST proxy). I had googled for a while but all seems take it for granted that implicitly flushing the response at the end of method. Here are the current codes with JAXB enabled I'm struggling to work on.
#Path("/chat")
public class LoadSimulator {
#Context private UriInfo uriInfo;
#Path("/outbound/{senderAddress}/requests")
#POST
#Consumes({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML})
#Produces({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML})
public Response createOutboundSMSMessage(OutboundSMSMessageRequest inSmsReq, #PathParam("senderAddress") String senderAddress) throws JAXBException {
String requestId = UUID.randomUUID().toString();
URI uri = uriInfo.getAbsolutePathBuilder().path(requestId).build();
ObjectFactory factory = new ObjectFactory();
ResourceReference resourceReference = new ResourceReference();
resourceReference.setResourceURL(uri.toString());
JAXBElement<ResourceReference> inSmsResponse = factory.createResourceReference(resourceReference);
return Response.created(uri).entity(inSmsResponse).build();
//// want to flush or commit the response explicitly like:
// out.flush();
// out.close();
//// Then sleep for a few second and fire a new REST request
// sleep(5);
// ....
// ClientConfig config = new DefaultClientConfig();
// String response = r.path("translate").queryParams(params).get(String.class);
}
}

If you could do what you're trying to do, you would exhaust the resources on your server because every request would take X seconds and you have a finite amount of threads available before the box cries uncle.
Without commenting on why you'd want to do this; If you used the #Singleton annotation for your LoadSimulator you could set up a thread that listens on a (concurrent) queue in #PostConstruct public void init() - that gets called when your servlet starts up.
#Singleton
#Path("/chat")
public class LoadSimulator {
private Thread restCaller;
private ConcurrentLinkedQueue<MyInfo> queue = new ConcurrentLinkedQueue<MyInfo>();
...
#PostConstruct public void init()
{
restCaller = new Thread(new MyRunnable(queue));
restCaller.start();
}
...
Then in your REST call, you'd put whatever information is needed to make the second REST call on that queue, and have the aforementioned thread pulling it off and making queries.

GET request using GWT to retrieve XML data?

Oh hello there, fellow SO members,
I have a web service that returns XML data using a simple get request that goes like this :
http://my-service:8082/qc/getData?paramX=0169&paramY=2
the service returns raw xml in the page according to the parameters' values.
I am trying to retrieve this data from a GET request in GWT using RequestBuilder, Request, etc.
However, the response gives me empty text, a Status code of ZERO (which doesn't mean anything and isn't supposed to happen), and so on.
Here's the simplified code that doesn't work.
public class SimpleXML implements EntryPoint {
public void onModuleLoad() {
this.doGet("http://my-service:8082/qc/getData", "0169", "2");
}
public void doGet(String serviceURL, String paramX, String paramY) {
final String getUrl = serviceURL + "?paramX=" + paramX + "&idTarification=" + paramY;
RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, getUrl);
try {
Request response = builder.sendRequest(null, new RequestCallback() {
#Override
public void onResponseReceived(Request request, Response response) {
response.getStatusCode(); // Gives me 0 (zero) :(
}
#Override
public void onError(Request request, Throwable exception) {
// ... doesn't matter for this example
}
});
} catch (RequestException e) {
// ... doesn't matter for this example
}
}
}
I don't get why this wouldn't work, since this is REALLY simple, I've seen tutorials and they all show me this way of doing things..
Thanks in advance

The reason is, that browsers do not allow cross-site requests with AJAX (see Same Origin Policy).
This means, that you can only call a service on the same server, same port (using the same protocol) as your HTML page. If you want to perform cross-site requests, you can use JSONP, as explained in http://code.google.com/webtoolkit/doc/latest/tutorial/Xsite.html.