In a legacy project I've inherited I've got a piece of code that
no longer works since the project was upgraded from Wicket 1.4 to
Wicket 6.
It's about rendering a component (a Wicket panel) into a string
in order to return it wrapped into a webservice reply.
The webservice is based on Wicket, too. The webservice is based
on a Javascript handshake - the client calls the service using a
token connecting the user to his current session he has on the
application, the service replies are rendered into an iframe and
deliver their data through postMessage.
Thus, when rendering a reply, I am basically rendering a Wicket
page within the context of my session.
Now one of my API's calls requires me to render a Wicket panel
into a String, which is then wrapped into JSON as part of the
respective call's reply.
The legacy code used to do this roughly like this (changes for
using the Wicket 6 API were applied, but this nevertheless never
worked):
- create a mock RequestCycle by creating a MockHttpSession, a
MockHttpServletRequest and a MockHttpServletResponse, glue
this all together to obtain a ServletWebRequest and a
BufferedWebResponse and finaly use use Application.createRequestCycle()
to create the RequestCycle object
- the component wrapped into a ComponentRenderingRequestHandler
- then this code is executed:
| try {
| requestCycle.scheduleRequestHandlerAfterCurrent(requestHandler);
| try {
| if ( !requestCycle.processRequestAndDetach() ) {
| requestCycle.scheduleRequestHandlerAfterCurrent(new
ErrorCodeRequestHandler((HttpServletResponse.SC_NOT_FOUND));
| }
| } finally {
| requestCycle.getResponse().close();
| }
| return requestCycle.getResponse().toString();
| } finally {
| requestCycle.detach();
| }
I must admit I could not have written this myself :)
Now when running this code, I run into two different
exceptions:
org.apache.wicket.WicketRuntimeException: Exception in rendering component:
[Profile [Component id = profile]]
at
org.apache.wicket.Component.internalRenderComponent(Component.java:2576)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1493)
~[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.internalRender(Component.java:2379)
[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.render(Component.java:2307)
[wicket-core-6.9.1.jar:6.9.1]
[...]
Caused by: java.lang.NullPointerException: null
at
org.apache.wicket.markup.html.internal.Enclosure.isVisible(Enclosure.java:143)
~[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.determineVisibility(Component.java:4363)
[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.internalBeforeRender(Component.java:916)
[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.beforeRender(Component.java:991)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.Component.internalPrepareForRender(Component.java:2214)
[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.render(Component.java:2303)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1390)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.MarkupContainer.renderAll(MarkupContainer.java:1554)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1529)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1484)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.markup.html.panel.DefaultMarkupSourcingStrategy.onComponentTagBody(DefaultMarkupSourcingStrategy.java:71)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.Component.internalRenderComponent(Component.java:2549)
[wicket-core-6.9.1.jar:6.9.1]
The enclosure's child component is null, as we see here:
| @Override
| public boolean isVisible()
| {
| return childComponent.determineVisibility() &&
super.isVisible();
| }
Below that exception I find the markup of a stack trace page in my logs.
Below that markup I get another stack trace:
java.lang.NullPointerException: null
at
org.apache.wicket.Component.internalPrepareForRender(Component.java:2224)
~[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Page.internalPrepareForRender(Page.java:241)
~[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Component.render(Component.java:2303)
~[wicket-core-6.9.1.jar:6.9.1]
at org.apache.wicket.Page.renderPage(Page.java:1010)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.handler.render.WebPageRenderer.renderPage(WebPageRenderer.java:121)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:271)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:165)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:861)
~[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
~[wicket-request-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:261)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:218)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:289)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:259)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:201)
[wicket-core-6.9.1.jar:6.9.1]
at
org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:282)
[wicket-core-6.9.1.jar:6.9.1]
Here the RequestCycle is null:
| if (setRenderingFlag)
| {
| // only process feedback panel when we are about to be
rendered.
| // setRenderingFlag is false in case prepareForRender is
called only to build component
| // hierarchy (i.e. in
BookmarkableListenerInterfaceRequestTarget).
| // prepareForRender(true) is always called before the actual
rendering is done so
| // that's where feedback panels gather the messages
|
| List<Component> feedbacks =
getRequestCycle().getMetaData(FEEDBACK_LIST);
To me it seems like I've got two different problems here:
- the component cannot be rendered because I'm doing something
fundamentally wrong, thus I'm not getting the expected output
- after the mock-RequestCycle's done with its work, there's no
RequestCycle set anymore, thus I cannot render the reply
I understand that my problem may be rather specific. And since
this is webservice that is already in use, I cannot just rewrite
it completely. Thus I would greatly appreciate any hint how i could
accomplish what the old code used to do before the Wicket upgrade?
Cheers,
M'bert
--
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