I have a simple application with a single JavaFX window. I'm sending in data to an Azure IoTHub inside a for loop. This for loop is in a JavaFX Task, and the for loop has a small delay (Thread.sleep(300)) so progress can be shown on the UI. I have 2 labels I want to update during the data transmission, always showing the latest sent in data. I have the following helper class for this:
public class DataHelper {
private StringProperty date = new SimpleStringProperty();
private StringProperty count = new SimpleStringProperty();
public DataHelper() {
}
public DataHelper(String date, String count) {
this.date.setValue(date);
this.count.setValue(count);
}
//getters and setters
}
And here is my sendErrorsToHub method inside my UI controller class:
private void sendErrorsToHub(List<TruckErrorForCloud> toCloud) {
DataHelper dataHelper = new DataHelper("", "");
Task task = new Task<DataHelper>() {
#Override
public DataHelper call() {
try {
int i = 0;
for (TruckErrorForCloud error : toCloud) {
Thread.sleep(300);
i++;
String strMessage = Utility.toPrettyJson(null, error);
if (strMessage != null) {
Message msg = new Message(strMessage);
msg.setMessageId(java.util.UUID.randomUUID().toString());
client.sendEventAsync(msg, null, null);
}
updateProgress(i, toCloud.size());
DataHelper dh = new DataHelper(error.getErrorTimeStamp().substring(0, error.getErrorTimeStamp().length() - 9),
String.valueOf(error.getCount()));
updateValue(dh);
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void updateValue(DataHelper value) {
super.updateValue(value);
dataHelper.setDate(value.getDate());
dataHelper.setCount(value.getCount());
}
//succeeded method omitted
};
dateValue.textProperty().bind(dataHelper.dateProperty());
countValue.textProperty().bind(dataHelper.countProperty());
progressBar.progressProperty().bind(task.progressProperty());
new Thread(task).start();
}
When I run the application, I constantly get IllegalStateException: Not on FX application threadexceptions, inside the updateValue method. As far as I understand the documentation, the whole point of the updateValue method, that it runs on the Application thread, and it can be used to pass a custom object, which can be used to update the UI.
What am I doing wrong then?
The bottom of the stacktrace with my classes is the following:
at eu.mantis.still_rca_simulator.gui.DataHelper.setDate(DataHelper.java:28)
at eu.mantis.still_rca_simulator.gui.GuiController$1.updateValue(GuiController.java:166)
at eu.mantis.still_rca_simulator.gui.GuiController$1.call(GuiController.java:155)
at eu.mantis.still_rca_simulator.gui.GuiController$1.call(GuiController.java:138)
(138 is the line Task task = new Task(), 155 updateValue(dh);, 166 dataHelper.setDate(value.getDate());)
updateValue does not automatically run on the application thread and it's not necessary to run it on the application thread since it takes care of updating the value property of Task on the application thread.
Your code in the overridden version updateValue executes logic on the background thread that needs to be run on the application thread though:
dataHelper.setDate(value.getDate());
dataHelper.setCount(value.getCount());
The bindings result in the text properties being updated from the background thread since the above code runs on the background thread.
In this case I recommend using a immutable DataHelper class and updating the ui using a listener to the value property:
Remove the updateValue override and the dataHelper local variable, initialize the gui with empty strings, if necessary, declare task as Task<DataHelper> task and do the following to update the gui:
task.valueProperty().addListener((o, oldValue, newValue) -> {
if (newValue != null) {
dateValue.setText(newValue.getDate());
countValue.setText(newValue.getCount());
}
});
You may also use Platform.runLater for those updates, since they don't happen frequently enough to result in issues that could be the result of using Platform.runLater too frequently.
Related
UPDATE:
I have a button on a JavaFx App that should do the login after user input email and password.
<Button fx:id="loginButton" layoutX="157.0" layoutY="254.0" mnemonicParsing="false" onAction="#login" prefHeight="30.0" prefWidth="172.0" text="Login" />
I have an ExecutorService on a JavaFX app. I created a task to search the DB. It executes the query well and gets the UserInfo object, the problem is, the ExecutorService is not passing the results to the main thread. This is the main code that is having a problem of null returned from the executor service:
public class LoginController {
#FXML
private Button loginButton;
#FXML
private Label afterLoginText;
#FXML
private TextField email;
#FXML
private PasswordField password;
#FXML
private Hyperlink hyperlink;
#FXML
private ProgressBar progressBar;
private Navegador navegador;
public void login(ActionEvent event) {
afterLoginText.setText("Login in, please wait...");
String emailText = email.getText();
String passwordText = password.getText();
DAOGeneric<UserInfo> dao = new DAOGeneric<>();
LoginAtDataBaseTask loginAtDataBaseTask = new LoginAtDataBaseTask(dao, emailText, passwordText);
progressBar.progressProperty().bind(loginAtDataBaseTask.progressProperty());
ExecutorService executorService = Executors.newSingleThreadExecutor();
Future future = executorService.submit(loginAtDataBaseTask);
loginAtDataBaseTask.setOnSucceeded(workerStateEvent -> {
UserInfo userInfo;
try {
userInfo = (UserInfo) future.get();
} catch (InterruptedException e) {
e.printStackTrace();
throw new RuntimeException(e);
} catch (ExecutionException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
if(userInfo == null){
System.out.println("User info is null");
}
else{
try {
changeToMainScreen(event, userInfo);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
//Set premium level if user have one
//Optional - show premium info
}
});
executorService.shutdown();
}
public void changeToMainScreen(ActionEvent event, UserInfo userInfo) throws IOException {
Stage stage = (Stage) ((Node)event.getSource()).getScene().getWindow();
runMainScreen("/mainScreen.fxml",stage, userInfo);
}
And here is the code of the LoginAtDataBaseTask Class:
public class LoginAtDataBaseTask extends Task <UserInfo> {
private static DAOGeneric<UserInfo> dao;
private static String email;
private static String password;
public LoginAtDataBaseTask(DAOGeneric<UserInfo> dao, String email, String password) {
this.dao = dao;
this.email = email;
this.password = password;
}
#Override
protected UserInfo call() {
return doLogin();
}
private UserInfo doLogin(){
final int maxProgress = 100;
List<UserInfo> usersList = dao.findByAnyParameter("email", email, UserInfo.class);
if(usersList.size() == 1){
updateProgress(99,maxProgress);
UserInfo user1 = usersList.get(0);
String passwordDecoded = DecoderMD5.StringToMD5(password);
if(user1.getUserPassword().equals(passwordDecoded)){
// afterLoginText.setText("Login Sucess!");
return user1;
}
else{
// afterLoginText.setText("Wrong Password!");
}
}
else if(usersList.size()>1){
//More than one user with same email on BD
// afterLoginText.setText("Error code 1 - report to administrator");
}
else if(usersList.size()==0){
// afterLoginText.setText("This email is not registered! Please register first!");
}
else{
//Erro at DAO Search
// afterLoginText.setText("Error code 2 - report to administrator");
}
return null;
}
}
I tried casting on many ways and using Future first to receive the submit and then calling get on the future object, but nothing seems to work. I have already readed the java documents of this related classes but i don't really understand why my object keeps null.
UPDATE: I put a setOnSucceeded but the future.get keeps returning null, and the main javafx ui keeps freezing. What am i keeping doing wrong and what can i do to solve it?
Why does get() return null?
This has to do with the fact that Task is, fundamentally, an implementation of Runnable. It is not an implementation of Callable. Therefore, you are calling #submit(Runnable) which returns a Future<?>1, meaning no result is expected. A Runnable cannot return a value. In other words, the call to #get() will always return null in this case.
But you should really be calling #execute(Runnable) when passing a Task to an ExecutorService, anyway. There's no reason to have a Future object representing the status of the Task. This is for at least two reasons:
The call to Future#get() is a blocking call. The whole purpose of Task is to communincate a result specifically back to the JavaFX Application Thread. And you must never block that thread, as doing so will lead to an unresponsive UI.
A Task is a FutureTask2, which means it is already a Future. If you really need to wait for a result (not on the FX thread), then you can just call #get() on the Task instance.
1. It really should have been defined to return Future<Void>
2. Note that the standard ExecutorService implementation, ThreadPoolExecutor, wraps all submitted Runnable and Callable objects in a FutureTask, at least by default.
How to get the result of a Task
As noted earlier, the purpose of Task (and the other javafx.concurrent classes) is to offload work to a background thread but communicate a result (as well as messages, progress, etc.) back to the JavaFX Application Thread. That thread specifically, not any other thread. But you must not block the FX thread. That means observing the task for completion, not waiting for it to complete. Then when it does complete, you react by doing what needs doing.
But how to get the value from a completed Task? You query its value property, which will be set to whatever is returned by the #call() method if and when the task succeeds. You can directly observe this property with a listener, if you want. Personally, I prefer using the onSucceeded and onFailed properties. For example:
Task<SomeObject> task = ...;
task.setOnSucceeded(e -> {
SomeObject result = task.getValue();
// do something with 'result'
});
task.setOnFailed(e -> {
task.getException().printStackTrace(); // or log it with a proper logging framework
// notify user of failure
});
executor.execute(task);
Note properties of Task like message, progress, value and so on are guaranteed to only be set by the FX thread. And the onXXX handlers are also guaranteed to be invoked only by the FX thread.
See Concurrency in JavaFX and javafx.concurrent documentation for more information.
I could not find a definitive answer to whether it is safe to spawn threads within session-scoped JSF managed beans. The thread needs to call methods on the stateless EJB instance (that was dependency-injected to the managed bean).
The background is that we have a report that takes a long time to generate. This caused the HTTP request to time-out due to server settings we can't change. So the idea is to start a new thread and let it generate the report and to temporarily store it. In the meantime the JSF page shows a progress bar, polls the managed bean till the generation is complete and then makes a second request to download the stored report. This seems to work, but I would like to be sure what I'm doing is not a hack.
Check out EJB 3.1 #Asynchronous methods. This is exactly what they are for.
Small example that uses OpenEJB 4.0.0-SNAPSHOTs. Here we have a #Singleton bean with one method marked #Asynchronous. Every time that method is invoked by anyone, in this case your JSF managed bean, it will immediately return regardless of how long the method actually takes.
#Singleton
public class JobProcessor {
#Asynchronous
#Lock(READ)
#AccessTimeout(-1)
public Future<String> addJob(String jobName) {
// Pretend this job takes a while
doSomeHeavyLifting();
// Return our result
return new AsyncResult<String>(jobName);
}
private void doSomeHeavyLifting() {
try {
Thread.sleep(SECONDS.toMillis(10));
} catch (InterruptedException e) {
Thread.interrupted();
throw new IllegalStateException(e);
}
}
}
Here's a little testcase that invokes that #Asynchronous method several times in a row.
Each invocation returns a Future object that essentially starts out empty and will later have its value filled in by the container when the related method call actually completes.
import javax.ejb.embeddable.EJBContainer;
import javax.naming.Context;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
public class JobProcessorTest extends TestCase {
public void test() throws Exception {
final Context context = EJBContainer.createEJBContainer().getContext();
final JobProcessor processor = (JobProcessor) context.lookup("java:global/async-methods/JobProcessor");
final long start = System.nanoTime();
// Queue up a bunch of work
final Future<String> red = processor.addJob("red");
final Future<String> orange = processor.addJob("orange");
final Future<String> yellow = processor.addJob("yellow");
final Future<String> green = processor.addJob("green");
final Future<String> blue = processor.addJob("blue");
final Future<String> violet = processor.addJob("violet");
// Wait for the result -- 1 minute worth of work
assertEquals("blue", blue.get());
assertEquals("orange", orange.get());
assertEquals("green", green.get());
assertEquals("red", red.get());
assertEquals("yellow", yellow.get());
assertEquals("violet", violet.get());
// How long did it take?
final long total = TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - start);
// Execution should be around 9 - 21 seconds
assertTrue("" + total, total > 9);
assertTrue("" + total, total < 21);
}
}
Example source code
Under the covers what makes this work is:
The JobProcessor the caller sees is not actually an instance of JobProcessor. Rather it's a subclass or proxy that has all the methods overridden. Methods that are supposed to be asynchronous are handled differently.
Calls to an asynchronous method simply result in a Runnable being created that wraps the method and parameters you gave. This runnable is given to an Executor which is simply a work queue attached to a thread pool.
After adding the work to the queue, the proxied version of the method returns an implementation of Future that is linked to the Runnable which is now waiting on the queue.
When the Runnable finally executes the method on the real JobProcessor instance, it will take the return value and set it into the Future making it available to the caller.
Important to note that the AsyncResult object the JobProcessor returns is not the same Future object the caller is holding. It would have been neat if the real JobProcessor could just return String and the caller's version of JobProcessor could return Future<String>, but we didn't see any way to do that without adding more complexity. So the AsyncResult is a simple wrapper object. The container will pull the String out, throw the AsyncResult away, then put the String in the real Future that the caller is holding.
To get progress along the way, simply pass a thread-safe object like AtomicInteger to the #Asynchronous method and have the bean code periodically update it with the percent complete.
Introduction
Spawning threads from within a session scoped managed bean is not necessarily a hack as long as it does the job you want. But spawning threads at its own needs to be done with extreme care. The code should not be written that way that a single user can for example spawn an unlimited amount of threads per session and/or that the threads continue running even after the session get destroyed. It would blow up your application sooner or later.
The code needs to be written that way that you can ensure that an user can for example never spawn more than one background thread per session and that the thread is guaranteed to get interrupted whenever the session get destroyed. For multiple tasks within a session you need to queue the tasks.
Also, all those threads should preferably be served by a common thread pool so that you can put a limit on the total amount of spawned threads at application level.
Managing threads is thus a very delicate task. That's why you'd better use the built-in facilities rather than homegrowing your own with new Thread() and friends. The average Java EE application server offers a container managed thread pool which you can utilize via among others EJB's #Asynchronous and #Schedule. To be container independent (read: Tomcat-friendly), you can also use the Java 1.5's Util Concurrent ExecutorService and ScheduledExecutorService for this.
Below examples assume Java EE 6+ with EJB.
Fire and forget a task on form submit
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
#EJB
private SomeService someService;
public void submit() {
someService.asyncTask();
// ... (this code will immediately continue without waiting)
}
}
#Stateless
public class SomeService {
#Asynchronous
public void asyncTask() {
// ...
}
}
Asynchronously fetch the model on page load
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
private Future<List<Entity>> asyncEntities;
#EJB
private EntityService entityService;
#PostConstruct
public void init() {
asyncEntities = entityService.asyncList();
// ... (this code will immediately continue without waiting)
}
public List<Entity> getEntities() {
try {
return asyncEntities.get();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new FacesException(e);
} catch (ExecutionException e) {
throw new FacesException(e);
}
}
}
#Stateless
public class EntityService {
#PersistenceContext
private EntityManager entityManager;
#Asynchronous
public Future<List<Entity>> asyncList() {
List<Entity> entities = entityManager
.createQuery("SELECT e FROM Entity e", Entity.class)
.getResultList();
return new AsyncResult<>(entities);
}
}
In case you're using JSF utility library OmniFaces, this could be done even faster if you annotate the managed bean with #Eager.
Schedule background jobs on application start
#Singleton
public class BackgroundJobManager {
#Schedule(hour="0", minute="0", second="0", persistent=false)
public void someDailyJob() {
// ... (runs every start of day)
}
#Schedule(hour="*/1", minute="0", second="0", persistent=false)
public void someHourlyJob() {
// ... (runs every hour of day)
}
#Schedule(hour="*", minute="*/15", second="0", persistent=false)
public void someQuarterlyJob() {
// ... (runs every 15th minute of hour)
}
#Schedule(hour="*", minute="*", second="*/30", persistent=false)
public void someHalfminutelyJob() {
// ... (runs every 30th second of minute)
}
}
Continuously update application wide model in background
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
#EJB
private SomeTop100Manager someTop100Manager;
public List<Some> getSomeTop100() {
return someTop100Manager.list();
}
}
#Singleton
#ConcurrencyManagement(BEAN)
public class SomeTop100Manager {
#PersistenceContext
private EntityManager entityManager;
private List<Some> top100;
#PostConstruct
#Schedule(hour="*", minute="*/1", second="0", persistent=false)
public void load() {
top100 = entityManager
.createNamedQuery("Some.top100", Some.class)
.getResultList();
}
public List<Some> list() {
return top100;
}
}
See also:
Spawning threads in a JSF managed bean for scheduled tasks using a timer
I tried this and works great from my JSF managed bean
ExecutorService executor = Executors.newFixedThreadPool(1);
#EJB
private IMaterialSvc materialSvc;
private void updateMaterial(Material material, String status, Location position) {
executor.execute(new Runnable() {
public void run() {
synchronized (position) {
// TODO update material in audit? do we need materials in audit?
int index = position.getMaterials().indexOf(material);
Material m = materialSvc.getById(material.getId());
m.setStatus(status);
m = materialSvc.update(m);
if (index != -1) {
position.getMaterials().set(index, m);
}
}
}
});
}
#PreDestroy
public void destory() {
executor.shutdown();
}
I am having two problems when trying to use "updateMessage" in a JavaFX task.
Issue #1
seems to be a known behavior, but I am not yet sure how exactly I can workaround it.This one is not (yet) critical to me.
The problem is that not all the updates I am performing in a background Task are displayed in the UI (at least the UI does not hang/freezes anymore, which was my initial issue).
My Code of the UI part:
TextArea console = new TextArea();
Button button01 = new Button("Start");
button01.setOnAction(new EventHandler() {
#Override
public void handle(Event event) {
if (ms.getState() == State.READY) {
ms.messageProperty().addListener(new ChangeListener<String>() {
#Override
public void changed(ObservableValue<? extends String> observable,
String oldValue, String newValue) {
console.appendText(newValue+"\n");
}
});
ms.start();
}
}
});
My Service:
public class MyService extends Service<Object> {
#Override
protected Task createTask() {
//here we use "MyTask" first to show problem #1
MyTask ct = new MyTask();
//here we use "MyTask2" first to show problem #2
// MyTask2 ct = new MyTask2();
try {
ct.call();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("MyService end");
return ct;
}
}
My Task (#1)
public class MyTask extends Task<Object> {
#Override
public EventHandler<WorkerStateEvent> call() {
System.out.println("call() is called");
if (Thread.currentThread().getName().equals("JavaFX Application Thread")){//yes, this might not be right, but if I do not do this, my stuff is executed twice because "call()" is called twice, but the textarea area is just updated in the second run (the non javafx application thread).
return null;
} else{
//actually here I want to do some 'heavy' stuff in the background
//and many things of this heavy stuff should be displayed / logged within the UI
//but very likely (hopefully) new messages (updateMessage) will not be send as fast as in the following loop
for (int i=0;i<10000000;i++){
updateMessage("This is update number'"+i+"' from the background thread");
}
Platform.runLater(new Runnable() {
#Override
public void run() {
try{
//here is the chance to get back to the view
}finally{
}
}
});
return null;
}
}
This basically works, but not every single loop is displayed in the UI.
How do I (correctly) make sure every loop is displayed?
Screenshot: Messages are displayed but not for every loop
Issue #2
Currently blocks my attempt to bring my little text-based game into a JavaFX application.
The main problem is that I am able to call "updateMessage" from the Task directly (see above), but not from a another (sub-)class which I would need to bring all message updates from my game (each message describes the progress of the game) to the UI.
The Task I use (Task #2):
public class MyTask2 extends Task<Object> {
#Override
public EventHandler<WorkerStateEvent> call() {
// ...
UITools myTools = new UITools();
myTools.logToUITest("Just one simple message");
// ...
Platform.runLater(new Runnable() {
#Override
public void run() {
try{
//here is the chance to get back to the view
}finally{
}
}
});
return null;
}
and the (sub-)class that I want to use to do the updateMessage (actually in my little game there would be even more classes that are called during the game and almost all of them trigger an update/message).
public class UITools {
public void logToUITest(String message){
updateMessage(message);
//how to allow 'updateMessage' from the Task to be executed from here?
}
This already results in "The method updateMessage(String) is undefined...".
How could I make it possible to call the updateMessage outside of the Task itself?
updateMessage() can only be called from within the call() method of a Task. It's a constraint imposed by the design of the Task class.
The missed message updates are due to the fact that there are too many updates and not all of them are forwarded to the event queue. Try to reduce the number of updates or sleep for a little while to separate them out in time
I've created a custom activity which contains as a Body another Activity.
[Browsable(false)]
public Activity Body { get; set; }
protected override void Execute(NativeActivityContext context)
{
ActivityInstance res = context.ScheduleActivity(Body, new CompletionCallback(OnExecuteComplete), OnFaulted);
}
private void OnFaulted(NativeActivityFaultContext faultContext, Exception propagatedException, ActivityInstance propagatedFrom)
{
throw new Exception(propagatedException.Message);
}
When an exception is thrown during the execution of the Body, ma handler for the OnFaulted is hit.
My execution starts with a call to static method Run of the WorkflowApplication class. My WorkflowApplication instance has a handler associated for the OnUnhandledException event.
instance.OnUnhandledException +=
delegate(WorkflowApplicationUnhandledExceptionEventArgs args)
{
Console.WriteLine(args.ExceptionSource);
waitEvent.Set();
return UnhandledExceptionAction.Cancel;
};
But regardless of what happens when the Activity hosted in the Body is executed, i never reach the handler defined above. I thought that if i throw an exception from the OnFaulted, i will be able to redirect the flow to the OnUnhandledException but i was wrong. Any ideas ?
I need this in order to centralize my errors, check them and display messages accordingly. Also i need a way to stop the execution and so on and i don't want to define handlers all over the application. Is there any way to accomplish this ?
As Will suggested, i will post what i did to handle my scenario.
Basically, in my custom activity i have hosted an Assign :
[Browsable(false)]
public Activity Body { get; set; }
Activity System.Activities.Presentation.IActivityTemplateFactory.Create(System.Windows.DependencyObject target)
{
return new Assignment()
{
Body = new Assign() { DisplayName = "" }
};
}
I've added this code to my Execute method :
ActivityInstance res = context.ScheduleActivity(Body, new CompletionCallback(OnExecuteComplete), OnFaulted);
I was trying to run this Assignment by giving an array a negative value as index and and an exception was thrown. This, somehow ended my execution but no handler for the events of my WorkflowApplication instance were hit.
Here is the method given as a callback when executing the body ( in our case the Assign activity ) :
private void OnFaulted(NativeActivityFaultContext faultContext, Exception propagatedException, ActivityInstance propagatedFrom)
{
faultContext.HandleFault();
CommunicationExtension ce = faultContext.GetExtension<CommunicationExtension>();
ITextExpression toTextExpression = (propagatedFrom.Activity as Assign).To.Expression as ITextExpression;
string valueTextExpression = string.Empty;
if ((propagatedFrom.Activity as Assign).Value != null)
{
if ((propagatedFrom.Activity as Assign).Value.Expression != null)
valueTextExpression = (propagatedFrom.Activity as Assign).Value.Expression.ToString();
}
if (ce != null)
{
ce.AddData(string.Format("{0} found on Assignment definition [{1} = {2}]", propagatedException.Message, toTextExpression.ExpressionText, valueTextExpression));
}
}
The trick was to call :
faultContext.HandleFault();
and use CommunicationExtension to allow me to to display the erros in the GUI.
The code for this class is trivial :
public class CommunicationExtension
{
public List<string> Messages { get; set; }
public CommunicationExtension()
{
Messages = new List<string>();
}
public void AddData(string message)
{
if (string.IsNullOrEmpty(message))
return;
Messages.Add(message);
}
}
Use this to add the extension:
CommunicationExtension ce = new CommunicationExtension();
instance.Extensions.Add(ce);
where instance is my WorkflowApplication instance.
I understood that for each instance of the workflow application we have one instance of its extension class. So i can send messages like this from all my custom activities in order to display their status.
I hope this scenario can help other people too.
I'm making a small game in LibGDX. I'm saving the player's username locally as well as on a server. The problem is that the application is not waiting for the result of the call so the online database's ID is not saved locally. Here's the overall flow of the code:
//Create a new user object
User user = new User(name);
//Store the user in the online database
NetworkService networkService = new NetworkService();
String id = networkService.saveUser(user);
//Set the newly generated dbase ID on the local object
user.setId(id);
//Store the user locally
game.getUserService().persist(user);
in this code, the id variable is not getting set because the saveUser function is returning immediately. How can I make the application wait for the result of the network request so I can work with results from the server communication?
This is the code for saveUser:
public String saveUser(User user) {
Map<String, String> parameters = new HashMap<String, String>();
parameters.put("action", "save_user");
parameters.put("json", user.toJSON());
HttpRequest httpGet = new HttpRequest(HttpMethods.POST);
httpGet.setUrl("http://localhost:8080/provisioner");
httpGet.setContent(HttpParametersUtils.convertHttpParameters(parameters));
WerewolfsResponseListener responseListener = new WerewolfsResponseListener();
Gdx.net.sendHttpRequest (httpGet, responseListener);
return responseListener.getLastResponse();
}
This is the WerewolfsResponseListener class:
class WerewolfsResponseListener implements HttpResponseListener {
private String lastResponse = "";
public void handleHttpResponse(HttpResponse httpResponse) {
System.out.println(httpResponse.getResultAsString());
this.lastResponse = httpResponse.getResultAsString();
}
public void failed(Throwable t) {
System.out.println("Saving user failed: "+t.getMessage());
this.lastResponse = null;
}
public String getLastResponse() {
return lastResponse;
}
}
The asynchrony you are seeing is from Gdx.net.sendHttpRequest. The methods on the second parameter (your WerewolfsResponseListener) will be invoked whenever the request comes back. The success/failure methods will not be invoked "inline".
There are two basic approaches for dealing with callbacks structured like this: "polling" or "events".
With polling, your main game loop could "check" the responseListener to see if its succeeded or failed. (You would need to modify your current listener a bit to disambiguate the success case and the empty string.) Once you see a valid response, you can then do the user.setId() and such.
With "events" then you can just put the user.setId() call inside the responseListener callback, so it will be executed whenever the network responds. This is a bit more of a natural fit to the Libgdx net API. (It does mean your response listener will need a reference to the user object.)
It is not possible to "wait" inline for the network call to return. The Libgdx network API (correctly) assumes you do not want to block indefinitely in your render thread, so its not structured for that (the listener will be queued up as a Runnable, so the earliest it can run is on the next render call).
I would not recommend this to any human being, but if you need to test something in a quick and dirty fashion and absolutely must block, this will work. There's no timeout, so again, be prepared for absolute filth:
long wait = 10;
while(!listener.isDone())
{
Gdx.app.log("Net", "Waiting for response");
try
{
Thread.sleep(wait *= 2);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
public static class BlockingResponseListener implements HttpResponseListener
{
private String data;
private boolean done = false;
private boolean succeeded = false;
#Override
public void handleHttpResponse(HttpResponse httpResponse)
{
Gdx.app.log("Net", "response code was "+httpResponse.getStatus().getStatusCode());
data = httpResponse.getResultAsString();
succeeded = true;
done = true;
}
#Override
public void failed(Throwable t)
{
done = true;
succeeded = false;
Gdx.app.log("Net", "Failed due to exception ["+t.getMessage()+"]");
}
public boolean succeeded()
{
return succeeded;
}
public boolean isDone()
{
return done;
}
public String getData()
{
return data;
}
}