Hi Anna,
There is no difference between the creation of layers that are on the
map at startup versus those that are off the map. The only thing
that differentiates between the two is their visibility setting. The
layers are all created via the ComponentFactory class via calls from
the LayerHandler (which itself was created by the ComponentFactory
via a call from the PropertyHandler).
- Don
On May 10, 2005, at 9:06 PM, Anna Forrest wrote:
> Hi,
>
> I have a query regarding class loaders and threading in openmap -
> in particular if there is any difference when loading a layer at
> startup as opposed to switching on a layer manually via the Layers
> menu or Edit Layers panel.
>
> I'm developing an XML plug in layer that loads images onto a map.
> The project is deployed/run via Ant 1.6.2.
> Since my XML layer uses JAXB to unmarshal XML files, I set the
> context classloader to be the current class loader before openmap
> starts.
>
> i.e. Before the OpenMapFrame gets created I do:
> Thread.currentThread().setContextClassLoader(this.getClass
> ().getClassLoader()); in my client. Note that this.getClass
> ().getClassLoader() is an instanceof
> net.jini.loader.pref.PreferredClassLoader and contains the jars
> required (i.e. jaxb and xml parser factories etc)
>
> A cut down version of the XML/JAXB code is:
> // Create a jaxbcontext capable of handling unmarshalling.
> JAXBContext jc = JAXBContext.newInstance
> ("com.classforge.jswat.client.layers.tiled.binding", this.getClass
> ().getClassLoader());
>
> // Create an unmarshaller
> Unmarshaller u = jc.createUnmarshaller();
>
> URL fileUrl = new URL(fileName);
>
> // Unmarshall an instance document into a tree of java content
> // objects composed of classes from the specified package
> Object obj = u.unmarshal(fileUrl);
>
> Now for the problem.
> If I include this XML layer in the openmap.startUpLayers list I get
> a ClassCastException when u.unmarshal(fileUrl) is performed, and
> the image loading never occurs. However, if I run the client
> without the XML layer in the startUpLayers list I select it
> manually via the Layers menu and the image loading works.
>
> The ClassCastException reported is:
> [java] java.lang.ClassCastException
> [java] at javax.xml.parsers.SAXParserFactory.newInstance
> (Unknown Source)
> [java] at
> javax.xml.bind.helpers.AbstractUnmarshallerImpl.getXMLReader
> (AbstractUnmarshallerImpl.java:74)
> [java] at
> javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal
> (AbstractUnmarshallerImpl.java:131)
> [java] at
> javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal
> (AbstractUnmarshallerImpl.java:136)
> [java] at
> javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal
> (AbstractUnmarshallerImpl.java:145)
> [java] at
> com.classforge.jswat.client.layers.tiled.XMLTiledImagePlugIn.listTiles
> (XMLTiledImagePlugIn.java:433)
> [java] at
> com.classforge.jswat.client.layers.tiled.XMLTiledImagePlugIn.loadTiles
> (XMLTiledImagePlugIn.java:168)
> [java] at
> com.classforge.jswat.client.layers.tiled.XMLTiledImagePlugIn.getRectan
> gle(XMLTiledImagePlugIn.java:104)
> [java] at com.bbn.openmap.plugin.PlugInLayer.prepare
> (PlugInLayer.java:324)
> [java] at
> com.bbn.openmap.layer.policy.StandardRenderPolicy.prepare
> (StandardRenderPolicy.java:67)
> [java] at com.bbn.openmap.layer.OMGraphicHandlerLayer
> $LayerWorker.construct(OMGraphicHandlerLayer.java:648)
> [java] at com.bbn.openmap.util.SwingWorker$2.run
> (SwingWorker.java:117)
> [java] at java.lang.Thread.run(Unknown Source)
>
>
> Note I have narrowed this problem down to the following:
> If layer is on at startup => then when the JAXB code above is
> executed the context class loader is not the same as current (and
> would have to include a hack in the JAXB code above to
> setContextClassLoader on current thread if not same as current).
> Note I have included a hack to reset the context class loader in
> the JAXB code above, and verified that this works, but it is not a
> very good solution.
>
> If layer is not on at startup, can select manually, and context
> class loader is same as current and JAXB code above executes ok.
>
> Can anyone tell me if openmap treats startup layers differently wrt
> threading/classloading - I thought setting the context class loader
> before calling any openmap code would ensure that any threads
> created by openmap would also use this context classloader?
>
> Thanks for any insight. Anna.
>
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Received on Fri May 13 2005 - 08:56:54 EDT