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Diffstat (limited to 'documentation/articles/UsingPolling.asciidoc')
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diff --git a/documentation/articles/UsingPolling.asciidoc b/documentation/articles/UsingPolling.asciidoc new file mode 100644 index 0000000000..1bd9119268 --- /dev/null +++ b/documentation/articles/UsingPolling.asciidoc @@ -0,0 +1,222 @@ +[[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); + } + }); + } + } +} +.... |