jimmyboix jimmyboix - 8 days ago 4
Java Question

Vaadin Table using threads only working one way

I have a class called HomeView that is used to extend a Vaadin Designer HTML class. This class has a Vaadin table that takes input from an uploaded file. So far the file uploads fine and I can split the file up into lines for testing. I was trying to use Vaadin threads to lock the session and go to the UploadFile class in which I will split up the file and add to a row in the table. I would then unlock the session, exit back to the background thread and the UI should update the table with new rows. This is not happening with the code below.

public void uploadSucceeded(Upload.SucceededEvent succeededEvent) {
//upload notification for upload
new Notification("File Uploaded Successfully",
Notification.Type.HUMANIZED_MESSAGE)
.show(Page.getCurrent());
//create new class for parsing logic
uf = new UploadFile();

new Thread(new Runnable() {
@Override
public void run() {
try {
getSession().lock();
uf.parseFile();
getSession().unlock();
} catch (IOException e) {
new Notification("Could not parse file type",
e.getMessage(),
Notification.Type.ERROR_MESSAGE)
.show(Page.getCurrent());
}
catch (UnsupportedOperationException e) {
e.printStackTrace();
} catch (ReadOnlyException e) {
e.printStackTrace();
}
}
}).start();
//outputFile.delete();
}
});


UploadFile class

public class UploadFile extends HomeView {

/**
*
*/
private static final long serialVersionUID = 839096232794540854L;

public void parseFile() throws IOException {

//container.removeAllItems();
BufferedReader reader = null;

reader = new BufferedReader(new InputStreamReader(new FileInputStream(outputFile.getAbsolutePath()), StandardCharsets.UTF_8));
String line;
while ((line = reader.readLine()) != null)
{
System.out.println("before add:" + uploadTable.size());
container = uploadTable.getContainerDataSource();
container.addItem("row3");
Item item2 = container.getItem("row3");
Property property2 = item2.getItemProperty("name");
property2.setValue("hello");
uploadTable.setContainerDataSource(container);
System.out.println("after add:" + uploadTable.size());

}
reader.close();
}
}


If I take the code above and just put it in place of the method call, then the table updates fine. The table is updating the row count in the background, it's just not refreshing the view. What am I missing to make the UI refresh?

@Override
public void uploadSucceeded(Upload.SucceededEvent succeededEvent) {
//upload notification for upload
new Notification("File Uploaded Successfully",
Notification.Type.HUMANIZED_MESSAGE)
.show(Page.getCurrent());
//create new class for parsing logic
uf = new UploadFile();

new Thread(new Runnable() {
@Override
public void run() {
try {
getSession().lock();

BufferedReader reader = null;

reader = new BufferedReader(new InputStreamReader(new FileInputStream(outputFile.getAbsolutePath()), StandardCharsets.UTF_8));
String line;
while ((line = reader.readLine()) != null)
{
System.out.println("before add:" + uploadTable.size());
container = uploadTable.getContainerDataSource();
container.addItem("row3");
Item item2 = container.getItem("row3");
Property property2 = item2.getItemProperty("name");
property2.setValue("hello");
uploadTable.setContainerDataSource(container);
System.out.println("after add:" + uploadTable.size());

}
reader.close();


getSession().unlock();
} catch (IOException e) {
new Notification("Could not parse file type",
e.getMessage(),
Notification.Type.ERROR_MESSAGE)
.show(Page.getCurrent());
}
catch (UnsupportedOperationException e) {
e.printStackTrace();
} catch (ReadOnlyException e) {
e.printStackTrace();
}
}
}).start();
//outputFile.delete();
}
});

Answer

UI.getCurrent() helper uses a ThreadLocal variable to get the active UI and it only works in a code executed in UI thread (e.g. a init method or button click listener). Get the UI reference before constructing the Thread and use the access method around your code that modifies UI. Do not use getSession().lock() or similar, you'll most likely do something wrong with that. Here is a simple usage example that should help you to resolve your use case as well.

            // Get the reference to UI to be modified
        final UI ui = getUI();

        new Thread() {
            @Override
            public void run() {
                // Do stuff that don't affect UI state here, e.g. potentially
                // slow calculation or rest call
                final double d = 1*1;

                ui.access(new Runnable() {
                    @Override
                    public void run() {
                        // This code here is safe to modify ui
                        Notification.show("The result of calculation is " + d);
                    }
                });
            }
       }.start();

In addition to properly synchronised UI access you need to have properly working push connection or polling to get changes to the client. If you want to use "real push" you need to add the annotation and add vaadin-push module to your app. Simpler method (and most often just as good) is just to enable polling:

ui.setPollInterval(1000); // 1000ms polling interval for client
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