I am trying to implement javadrone (AR.Drone Java API) in my project. However, it was occurred state changed error when I compile my java code and try to fly it. I was able to send command to AR.Drone and fly for the first time. After successfully take off for the first time,it won't take off again due to "state changed" error. I have no idea what went wrong in my code. Please help me out. Thanks! There are 3 files that are required in this project. My java file(arDroneFrame.java),NavData.java(from javadrone), and ARDrone.java(from javadrone).The The main java file: arDroneFrame.java. When I press the TakeOff button, it should make AR.Drone fly and land afterwards.
In my arDroneFrame.java,
private void jButtonTakeOffActionPerformed(java.awt.event.ActionEvent evt) {
com.codeminders.ardrone.ARDrone drone;
try{
drone = new com.codeminders.ardrone.ARDrone();
drone.connect();
drone.clearEmergencySignal();
// Wait until drone is ready
drone.waitForReady(CONNECT_TIMEOUT);
// do TRIM operation
drone.trim();
// Take off
System.err.println("Taking off");
drone.takeOff();
// Fly a little :)
Thread.sleep(5000);
//Land
System.err.println("Landing");
drone.land();
// Give it some time to land
Thread.sleep(2000);
// Disconnect from the done
drone.disconnect();
} catch (UnknownHostException ex) {
Logger.getLogger(arDroneFrame.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(arDroneFrame.class.getName()).log(Level.SEVERE, null, ex);
} catch (InterruptedException ex) {
Logger.getLogger(arDroneFrame.class.getName()).log(Level.SEVERE, null, ex);
}
}
In ARDrone.java, I had commented out some java coding.This is because only when I comment out those java code, it can only works. If I uncomment them, my program will be stuck there (no respond at all).
public void waitForReady(long how_long) throws IOException
{
/*long since = System.currentTimeMillis();
synchronized(state_mutex)
{
while(true)
{
if((System.currentTimeMillis() - since) >= how_long)
{
try
{
disconnect();
} catch(IOException e)
{
}
// Timeout, too late
throw new IOException("Timeout connecting to ARDrone");
} else if(state == State.DEMO)
{
return; // OK! We are now connected
} else if(state == State.ERROR || state == State.DISCONNECTED)
{
throw new IOException("Connection Error");
}
long p = Math.min(how_long - (System.currentTimeMillis() - since), how_long);
if(p > 0)
{
try
{
state_mutex.wait(p);
} catch(InterruptedException e)
{
// Ignore
}
}
}
}*/
while(state == State.DEMO)
{
System.out.println("Changed to DEMO !");
return; // OK! We are now connected
}
}
Program Output:
126 [Thread-7] DEBUG ardrone.ARDrone - State changed from TAKING_OFF to ERROR with exception
java.lang.NullPointerException
at com.codeminders.ardrone.NavData$FlyingState.fromControlState(NavData.java:58)
at com.codeminders.ardrone.NavData.getFlyingState(NavData.java:622)
at com.codeminders.ardrone.ARDrone.navDataReceived(ARDrone.java:431)
at com.codeminders.ardrone.NavDataReader.run(NavDataReader.java:92)
at java.lang.Thread.run(Thread.java:745)
Related
My test method looks like this:
private static System.Timers.Timer _myTimer;
static void Main(string[] args)
{
using (_myTimer = new System.Timers.Timer(1000))
{
_myTimer.Elapsed += (o, e) => Console.WriteLine($"timer elapsed");
_myTimer.AutoReset = true;
_myTimer.Enabled = true;
Thread.Sleep(4000); // let the timer fire a couple of times
} // dispose timer?
Thread.Sleep(2000); // timer won't fire here
try
{
Console.WriteLine($"no problem accessing _myTimer: {_myTimer.Interval}"); // this won't throw an ObjectDisposedException on _myTimer
}
catch (Exception ex)
{
Console.WriteLine($"Exception: {ex}");
}
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
try
{
Console.WriteLine($"no problem accessing _myTimer: {_myTimer.Interval}"); // still no ObjectDisposedException
}
catch (Exception ex)
{
Console.WriteLine($"Exception: {ex}");
}
try
{
//_myTimer.Start(); // throws the ObjectDisposedException
_myTimer.Dispose(); // does not throw the ObjectDisposedException
}
catch (Exception ex)
{
Console.WriteLine($"Exception: {ex}");
}
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
try
{
Console.WriteLine($"no problem accessing _myTimer: {_myTimer.Interval}"); // still no ObjectDisposedException
}
catch (Exception ex)
{
Console.WriteLine($"Exception: {ex}");
}
Console.WriteLine("Press any key to continue...");
Console.ReadLine();
}
I would expect to get the ObjectDisposedException after leaving the using block.
Accessing the _myTimer.Interval works all the way to the end of the program. Also, I can call _myTimer.Dispose() anytime. Even waiting for the GarbageCollector does not help to get the ObjectDisposedException.
However, I do get the ObjectDisposedException if I call _myTimer.Start() after leaving the using block.
How can _myTimer be around for the entire lifetime of my program?
Calling Dispose doesn't remove the object or references to it. It will not be GCed as long as there are references to it. Dispose releases unmanaged resources within the object, which is likely but by no means guaranteed to cause at least some of its methods to stop working and start throwing ObjectDisposedException.
I have looked at the examples for subscribing to a NodeId and im wondering how I could stop/delete a subscription afterward.
Eclipse Milo v0.3.8 Client.
Here's what I've tried.
protected boolean unsubscribe(TransactionDefinition transactionDefinition) {
// Finds the mathing TransactionDefinition from the map where all subscriptions
// are stored, together with the clientHandle.
// private Map<UInteger, TransactionDefinition> subscriptions = new HashMap<>();
try {
UInteger subscriptionClientHandle = null;
for (Map.Entry<UInteger, TransactionDefinition> entry : subscriptions.entrySet()) {
if (entry.getValue().equals(transactionDefinition))
subscriptionClientHandle = entry.getKey();
}
if (subscriptionClientHandle == null) return false;
try {
client.getSubscriptionManager().deleteSubscription(subscriptionClientHandle).get();
return true;
} catch (Exception e) {
log.error("Subscription not found: {}", e.getMessage(), e.getCause());
e.printStackTrace();
}
} catch (ClassCastException e) {
log.error("TransactionDefinition trigger not found. {}", e.getMessage(), e.getCause());
e.printStackTrace();
}
return false;
}
UaSubscription has a deleteMonitoredItems method on it.
UaSubscriptionManager has a deleteSubscription method on it.
You could also call either of these services "manually" by invoking the "raw" service methods on the UaClient instance.
I used ListeningExecutorService of guava in my project, got confused about the exception handling.
I used a thread pool, submit a task to it, and set a timeout to the listenableFuture, and add a callback to it.
final ListeningExecutorService threadPool = MoreExecutors.listeningDecorator(Executors.newCachedThreadPool());
Futures.addCallback(listenableFuture, new FutureCallback<**>() {
#Override
public void onSuccess(#Nullable ** data) {
xxxxxxx;
}
public void onFailure(Throwable t) {
xxxxxxxxxx;
if (t instanceof CancellationException) {
throw new QueryException("yyyy");
} else {
throw new QueryException("zzzzz");
}
}
});
I can't catch the exception inside the callback. So I use another ListenableFuture to get the exception
ListenableFuture allFutures = Futures.allAsList(allFuturesList);
try {
allFutures.get();
} catch (CancellationException ce) {
throw new QueryException("");
} catch (InterruptedException t) {
throw new QueryException("");
} catch (ExecutionException e) {
Throwable t = e.getCause();
if (t instanceof QueryException)
throw (QueryException) t;
else
throw new QueryException();
} catch (QueryException qe) {
throw qe;
} catch (Exception e) {
throw new QueryException();
} finally {
}
But I when the callback throw a QueryException, the allFutures can't catch it, allFutures can only catch a CancellationException without the detail error message.
How can I get my detail error message?
Futures.allAsList doesn't do what you expect it to do
From the Javadoc: (emphasis is from me)
Canceling this future will attempt to cancel all the component futures, and if any of the provided futures fails or is canceled, this one is, too.
What you should probably do is create your own aggregating future. You can base your code on Guava's own internal mechanism. See the source code for more info.
Anyways, do not throw exceptions in your FutureCallback::onFailure method.
I have a snippet to download a file from jersey 2.22,
StreamingOutput stream = (OutputStream os) -> {
try {
os.write( get a byte array here);
} catch (Exception e) {
LOGGER.error("Failed to fetch file, id:" + fileName, e);
throw new Exception());
}
};
the above code is working, but i'm wondering if the output stream I'm writing in needs to close.
I searched jersey's source code, in OutboundMessageContext
public void close() {
if(this.hasEntity()) {
try {
OutputStream e = this.getEntityStream();
e.flush();
e.close();
} catch (IOException var10) {
Logger.getLogger(OutboundMessageContext.class.getName()).log(Level.FINE, var10.getMessage(), var10);
} finally {
if(!this.committingOutputStream.isClosed()) {
try {
this.committingOutputStream.close();
} catch (IOException var9) {
Logger.getLogger(OutboundMessageContext.class.getName()).log(Level.FINE, var9.getMessage(), var9);
}
}
}
}
}
this method is to close entity stream. I'm not sure if this is the right close method working with StreamingOutput, can anyone help?
When /api/upload REST endpoint is accessed I have a UploadController that uses a service UploadService to upload a file to an ftp server with org.apache.commons.net.ftp.FTPClient. I would like to be able to send information back to the user if the ftp client was unable to connect or timed out, or successfully sent the file. I have some IOException handling, but I don't know how to turn that around and send it back to the front-end. Any help appreciated, thanks!
public void upload(InputStream inputStream) {
String filename = "file.txt"
client = new FTPClient();
try {
client.connect("ftpsite");
client.login("username", "password");
client.storeFile(filename, inputStream);
} catch (IOException ioe) {
ioe.printStackTrace();
} finally {
try {
if (inputStream!= null) {
inputStream.close();
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
return null;
}
You should throw a new Exception in your catch statement.
For example, you could create a RequestTimeoutException class:
#ResponseStatus(HttpStatus.REQUEST_TIMEOUT)
public class RequestTimeoutException extends RuntimeException { }
and then throw it when need be:
catch (IOException ioe) {
//do some logging while you're at it
throw new RequestTimeoutException();
}