[https://github.com/apache/wicket/issues/1492] make partial page upda…

wicket-core/src/main/java/org/apache/wicket/ajax/AjaxRequestHandler.java

@@ -80,13 +80,13 @@ public class AjaxRequestHandler extends AbstractPartialPageRequestHandler implem
 	/**
 	 * Collector of page updates.
 	 */
-	private final PartialPageUpdate update;
+	private PartialPageUpdate update;
 
 	/** a set of listeners */
-	private Set<AjaxRequestTarget.IListener> listeners = null;
+	protected Set<AjaxRequestTarget.IListener> listeners = null;
 
 	/** */
-	private final Set<ITargetRespondListener> respondListeners = new HashSet<>();
+	protected final Set<ITargetRespondListener> respondListeners = new HashSet<>();
 
 	/** see https://issues.apache.org/jira/browse/WICKET-3564 */
 	protected transient boolean respondersFrozen;
@@ -103,8 +103,17 @@ public class AjaxRequestHandler extends AbstractPartialPageRequestHandler implem
 	public AjaxRequestHandler(final Page page)
 	{
 		super(page);
+	}
 
-		update = new XmlPartialPageUpdate(page)
+	/**
+	 * Factory method for {@link PartialPageUpdate}'s
+	 *
+	 * @param page The {@link Page}
+	 * @return an instance of {@link PartialPageUpdate}
+	 */
+	protected PartialPageUpdate newPartialPageUpdate(final Page page)
+	{
+		return new XmlPartialPageUpdate(page)
 		{
 			/**
 			 * Freezes the {@link AjaxRequestHandler#listeners} before firing the event and
@@ -130,7 +139,7 @@ protected void onBeforeRespond(final Response response)
 			/**
 			 * Freezes the {@link AjaxRequestHandler#listeners}, and does not un-freeze them as the
 			 * events will have been fired by now.
-			 * 
+			 *
 			 * @param response
 			 *            the response to write to
 			 */
@@ -143,7 +152,7 @@ protected void onAfterRespond(final Response response)
 				if (listeners != null)
 				{
 					final Map<String, Component> components = Collections
-						.unmodifiableMap(markupIdToComponent);
+							.unmodifiableMap(markupIdToComponent);
 
 					for (AjaxRequestTarget.IListener listener : listeners)
 					{
@@ -174,13 +183,16 @@ public void addListener(AjaxRequestTarget.IListener listener) throws IllegalStat
 	@Override
 	public PartialPageUpdate getUpdate()
 	{
+		if (update == null) {
+			update = newPartialPageUpdate(getPage());
+		}
 		return update;
 	}
 
 	@Override
 	public final Collection<? extends Component> getComponents()
 	{
-		return update.getComponents();
+		return getUpdate().getComponents();
 	}
 
 	/**
@@ -194,7 +206,7 @@ public void detach(final IRequestCycle requestCycle)
 			logData = new PageLogData(getPage());
 		}
 
-		update.detach(requestCycle);
+		getUpdate().detach(requestCycle);
 	}
 
 	/**
@@ -206,7 +218,7 @@ public boolean equals(final Object obj)
 		if (obj instanceof AjaxRequestHandler)
 		{
 			AjaxRequestHandler that = (AjaxRequestHandler)obj;
-			return update.equals(that.update);
+			return getUpdate().equals(that.update);
 		}
 		return false;
 	}
@@ -218,7 +230,7 @@ public boolean equals(final Object obj)
 	public int hashCode()
 	{
 		int result = "AjaxRequestHandler".hashCode();
-		result += update.hashCode() * 17;
+		result += getUpdate().hashCode() * 17;
 		return result;
 	}
 
@@ -265,7 +277,7 @@ public final void respond(final IRequestCycle requestCycle)
 		final String encoding = app.getRequestCycleSettings().getResponseRequestEncoding();
 
 		// Set content type based on markup type for page
-		update.setContentType(response, encoding);
+		getUpdate().setContentType(response, encoding);
 
 		// Make sure it is not cached by a client
 		response.disableCaching();
@@ -276,7 +288,7 @@ public final void respond(final IRequestCycle requestCycle)
 		// WICKET-7074 we need to write to a temporary buffer, otherwise, if an exception is produced,
 		// and a redirect is done we will end up with a malformed XML
 		final StringResponse bodyResponse = new StringResponse();
-		update.writeTo(bodyResponse, encoding);
+		getUpdate().writeTo(bodyResponse, encoding);
 		if (filters == null || filters.isEmpty())
 		{
 			response.write(bodyResponse.getBuffer());
@@ -290,7 +302,7 @@ public final void respond(final IRequestCycle requestCycle)
 
 	private boolean shouldRedirectToPage(IRequestCycle requestCycle)
 	{
-		if (update.containsPage())
+		if (getUpdate().containsPage())
 		{
 			return true;
 		}
@@ -333,7 +345,7 @@ private CharSequence invokeResponseFilters(final StringResponse contentResponse,
 	@Override
 	public String toString()
 	{
-		return "[AjaxRequestHandler@" + hashCode() + " responseObject [" + update + "]";
+		return "[AjaxRequestHandler@" + hashCode() + " responseObject [" + getUpdate() + "]";
 	}
 
 	/**

wicket-core/src/main/java/org/apache/wicket/page/PartialPageUpdate.java

@@ -75,7 +75,7 @@ public abstract class PartialPageUpdate
 	 * Length of the script block that combined scripts are wrapped in. This includes the script tag,
 	 * CDATA and if CSP is enabled also the nonce.
 	 */
-	private static final int SCRIPT_BLOCK_LENGTH = 100;
+	protected static final int SCRIPT_BLOCK_LENGTH = 100;
 
 	/**
 	 * A list of scripts (JavaScript) which should be executed on the client side before the