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---
title: Using Polling
order: 17
layout: page
---
[[using-polling]]
Using Polling
-------------
To set up polling for your UI, you only need to set a poll interval
using `UI.setPollInterval(timeout)`. By doing this the browser will poll
the server each "timeout" ms and retrieve any possibly pending changes.
You can test this in practice by creating a small application which
initially creates a small "please wait" UI and then loads the actual UI
in a background thread.
[source,java]
....
public class PollingUI extends UI {
@WebServlet(value = "/*")
@VaadinServletConfiguration(productionMode = false, ui = Polling7UI.class)
public static class Servlet extends VaadinServlet {
}
@Override
protected void init(VaadinRequest request) {
setContent(new Label("Loading data, please wait..."));
setPollInterval(1000);
new Thread(new Loader()).start();
}
class Loader implements Runnable {
@Override
public void run() {
// Simulate a heavy database operation
try {
Thread.sleep(4500);
} catch (InterruptedException e) {
}
// Wrap UI updates in access to properly deal with locking
access(new Runnable() {
@Override
public void run() {
setContent(new Label("This is the real content"));
// Stop polling once the update is done
setPollInterval(-1);
}
});
}
}
}
....
For more information regarding locking the session, see [Using server
initiated events]
[[polling-for-multiple-components]]
Polling for multiple components
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If you have the situation that several components need polling at some
point you should use some kind of Manager to handle the polling, for it
can only be set UI-wise (which makes perfectly sense)
A simple `UIPollingManager` which always uses the lowest registered
`intervalTime` could look like this:
[source,java]
....
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import com.vaadin.ui.UI;
public class UIPollingManager
{
private Map<UI, Map<Object, Integer>> pollRequests;
public UIPollingManager()
{
pollRequests = new WeakHashMap<>(); // Let's use weak references in case someone forgets to unregister properly
}
/**
* Registers a poll request for the given UI. Sets the pollInterval of this UI to the lowest registered interval.
* @param ui
* @param requestor
* @param pollIntervalInMillis poll interval in milliseconds
*/
public void registerPollRequest(UI ui, Object requestor, int pollIntervalInMillis)
{
Map<Object, Integer> uiRequests = pollRequests.get(ui);
if (uiRequests == null)
{
uiRequests = new HashMap<>();
pollRequests.put(ui, uiRequests);
}
uiRequests.put(requestor, pollIntervalInMillis);
setPollInterval(ui);
}
/**
* Removes a poll request for the given UI (if existent). Sets the pollInterval of this UI to the lowest registered interval
* remaining or -1 if no more requests exist for the UI
* @param ui
* @param requestor
*/
public void unregisterPollRequest(UI ui, Object requestor)
{
Map<Object, Integer> uiRequests = pollRequests.get(ui);
if (uiRequests != null)
{
uiRequests.remove(requestor);
// Remove the UI from our map if no requests exist anymore
if (uiRequests.size() <= 0) pollRequests.remove(ui);
}
setPollInterval(ui);
}
/**
* Removes all poll requests of the given UI and sets the pollInterval to -1
* @param ui
*/
public void unregisterAllPollRequests(UI ui)
{
pollRequests.remove(ui);
ui.setPollInterval(-1);
}
/**
* Sets the pollInterval of the given UI to the lowest registered interval time of this UI
* @param ui
*/
private void setPollInterval(UI ui)
{
Map<Object, Integer> uiRequests = pollRequests.get(ui);
if (uiRequests != null)
{
ui.setPollInterval(getLowestNumber(uiRequests.values()));
}
}
/**
* Returns the lowest number of a given Integer-Collection. Returns -1 if no valid Integer is included in the collection.
* @param intervalArray
* @return
*/
private Integer getLowestNumber(Collection<Integer> intervalArray)
{
Integer lowestNum = null;
for (Integer i : intervalArray)
{
if (i != null && ( lowestNum == null || i < lowestNum )) lowestNum = i;
}
if (lowestNum == null) return -1;
else
return lowestNum;
}
}
....
The changed example could then look like this:
[source,java]
....
public class Polling7UI extends UI {
private UIPollingManager pollingManager; // Instantiate this via Spring or get it via Singleton or whatever
@WebServlet(value = "/*")
@VaadinServletConfiguration(productionMode = false, ui = Polling7UI.class)
public static class Servlet extends VaadinServlet {
}
@Override
protected void init(VaadinRequest request) {
setContent(new Label("Loading data, please wait..."));
Loader loader = new Loader();
pollingManager.registerPollRequest(this, loader, 1000);
new Thread(loader).start();
}
class Loader implements Runnable {
private UI ui;
private UIPollingManager pollingManager;
public Loader( UI ui, UIPollingManager pollingManager )
{
this.ui = ui;
this.pollingManager = pollingManager;
}
@Override
public void run() {
// Simulate a heavy database operation
try {
Thread.sleep(4500);
} catch (InterruptedException e) {
}
final Loader loader = this;
// Wrap UI updates in access to properly deal with locking
access(new Runnable() {
@Override
public void run() {
setContent(new Label("This is the real content"));
// Stop polling once the update is done
pollingManager.unregisterPollRequest(ui, loader);
}
});
}
}
}
....
|
