Package com.vaadin.flow.server

Interface StreamVariable

All Superinterfaces:

Serializable

public interface StreamVariable
extends Serializable

StreamVariable is a special kind of variable whose value is streamed to an OutputStream provided by the getOutputStream() method. E.g. in web terminals StreamVariable can be used to send large files from browsers to the server without consuming large amounts of memory.

Note, writing to the OutputStream is not synchronized by the handler (to avoid stalls in other operations when e.g. streaming to a slow network service or file system). If UI is changed as a side effect of writing to the output stream, developer must handle synchronization manually.

Since:

1.0.

Author:

Vaadin Ltd

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	StreamVariable.StreamingEndEvent	Event passed to streamingFinished(StreamingEndEvent) method the contents have been streamed to StreamVariable successfully.
static interface	StreamVariable.StreamingErrorEvent	Event passed to streamingFailed(StreamingErrorEvent) method when the streaming ended before the end of the input.
static interface	StreamVariable.StreamingEvent	Streaming event interface.
static interface	StreamVariable.StreamingProgressEvent	Event passed to onProgress(StreamingProgressEvent) method during the streaming progresses.
static interface	StreamVariable.StreamingStartEvent	Event passed to streamingStarted(StreamingStartEvent) method before the streaming of the content to StreamVariable starts.

Method Summary

Modifier and Type	Method	Description
OutputStream	getOutputStream()	Invoked when a new upload arrives, after streamingStarted(StreamingStartEvent) method has been called.
boolean	isInterrupted()	If this method returns true while the content is being streamed the handler is told to stop receiving the current upload.
boolean	listenProgress()	Whether the onProgress(StreamingProgressEvent) method should be called during the upload.
void	onProgress(StreamVariable.StreamingProgressEvent event)	This method is called if listenProgress() returns true when the streaming starts.
void	streamingFailed(StreamVariable.StreamingErrorEvent event)	This method is called when the streaming has failed.
void	streamingFinished(StreamVariable.StreamingEndEvent event)	This method is called when the streaming has finished.
void	streamingStarted(StreamVariable.StreamingStartEvent event)	This method is called when the streaming starts.

Method Details

getOutputStream

OutputStream getOutputStream()

Invoked when a new upload arrives, after streamingStarted(StreamingStartEvent) method has been called. The implementation will write the streamed variable to the returned output stream.

Returns:

Stream to which the uploaded file should be written.

listenProgress

boolean listenProgress()

Whether the onProgress(StreamingProgressEvent) method should be called during the upload.

onProgress(StreamingProgressEvent) is called in a synchronized block when the content is being received. This is potentially bit slow, so we are calling that method only if requested. The value is requested after the streamingStarted(StreamingStartEvent) event, but not after reading each buffer.

Returns:

true if this StreamVariable wants to by notified during the upload of the progress of streaming.

See Also:

• onProgress(StreamingProgressEvent)

onProgress

void onProgress(StreamVariable.StreamingProgressEvent event)

This method is called if listenProgress() returns true when the streaming starts.

Parameters:

event - streaming progress event

streamingStarted

void streamingStarted(StreamVariable.StreamingStartEvent event)

This method is called when the streaming starts.

Parameters:

event - streaming start event

streamingFinished

void streamingFinished(StreamVariable.StreamingEndEvent event)

This method is called when the streaming has finished.

Parameters:

event - streaming end event

streamingFailed

void streamingFailed(StreamVariable.StreamingErrorEvent event)

This method is called when the streaming has failed.

Parameters:

event - streaming error event

isInterrupted

boolean isInterrupted()

If this method returns true while the content is being streamed the handler is told to stop receiving the current upload.

Note, the usage of this method is not synchronized over the Application instance like other methods. The implementation should only return a boolean field and especially not modify UI or implement a synchronization by itself.

Returns:

true if the streaming should be interrupted as soon as possible.