MalformedUrlException o_O

...
Caused by:
java.net.MalformedURLException
        at java.net.URL.(URL.java:601)
        at java.net.URL.(URL.java:464)
        at java.net.URL.(URL.java:413)
        at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(Unknown Source)
        at org.apache.xerces.impl.XMLVersionDetector.determineDocVersion(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
        at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
        at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
        at org.apache.xalan.templates.StylesheetRootProxy.(Unknown Source)

OR

...
java.net.MalformedURLException
 at java.net.URL.(URL.java:601)
 at java.net.URL.(URL.java:464)
 at java.net.URL.(URL.java:413)
 at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:649)
 at com.sun.org.apache.xerces.internal.impl.XMLVersionDetector.determineDocVersion(XMLVersionDetector.java:186)
 at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:772)
 at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
 at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
 at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
 at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
 at javax.xml.parsers.SAXParser.parse(SAXParser.java:395)

...may just mean that you pushed a null InputSteam into parser.

For example this piece of code would produce such exception trace:

SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
parser.parse(new InputSource((InputStream) null), new DefaultHandler());

It also may be done in less explicit way, for example with an XSLT parser being given XSLT source with null InputSteam inside (which actually was the issue I originally faced).

DSRA0080E Data Store Adapter exception on IBM WebSphere EJB client

More like a hint for myself :)

Exception like this:

...
Caused by: com.ibm.ws.rsadapter.exceptions.DataStoreAdapterException: DSRA0080E: An exception was received by the Data Store Adapter. See original exception message: com/ibm/websphere/rsadapter/DataStoreHelper.doConnectionSetupPerGetConnection(Ljava/sql/Connection;ZLjava/lang/Object;)Z.
  at com.ibm.ws.rsadapter.spi.WSRdbManagedConnectionImpl.getConnection(WSRdbManagedConnectionImpl.java:3503)
  at com.ibm.ws.rsadapter.spi.WSDefaultConnectionManagerImpl.allocateConnection(WSDefaultConnectionManagerImpl.java:91)
  at com.ibm.ws.rsadapter.jdbc.WSJdbcDataSource.getConnection(WSJdbcDataSource.java:646)
  ... 22 more
Caused by: java.lang.AbstractMethodError: com/ibm/websphere/rsadapter/DataStoreHelper.doConnectionSetupPerGetConnection(Ljava/sql/Connection;ZLjava/lang/Object;)Z
  at com.ibm.ws.rsadapter.spi.WSRdbManagedConnectionImpl.getConnection(WSRdbManagedConnectionImpl.java:3482)
  ... 24 more

may be caused by running EJB client application with different (e.g. non-IBM) Java VM.

Meaningful error message from IBM WebSphere

Seeing this on your WebSphere application server startup?

00000000 ContainerHelp E   WSVR0501E: Error creating component com.ibm.ws.cluster.runtime.ProcessRuntimeImpl
java.lang.NoClassDefFoundError: com.ibm.websphere.cluster.topography.DescriptionManagerFactory (initialization failure)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:140)
        at com.ibm.ws.cluster.runtime.ProcessRuntimeImpl.initialize(ProcessRuntimeImpl.java:366)
        at com.ibm.ws.runtime.component.ContainerHelper.initWsComponent(ContainerHelper.java:1166)
        at com.ibm.ws.runtime.component.ContainerHelper.initializeComponent(ContainerHelper.java:1073)
        at com.ibm.ws.runtime.component.ContainerHelper.initializeComponents(ContainerHelper.java:874)
        at com.ibm.ws.runtime.component.ContainerImpl.initializeComponents(ContainerImpl.java:780)
        at com.ibm.ws.runtime.component.ContainerImpl.initializeComponents(ContainerImpl.java:754)
        at com.ibm.ws.runtime.component.ServerImpl.initialize(ServerImpl.java:350)
        at com.ibm.ws.runtime.WsServerImpl.bootServerContainer(WsServerImpl.java:280)
        at com.ibm.ws.runtime.WsServerImpl.start(WsServerImpl.java:214)
        at com.ibm.ws.runtime.WsServerImpl.main(WsServerImpl.java:666)
        at com.ibm.ws.runtime.WsServer.main(WsServer.java:59)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:45)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
        at java.lang.reflect.Method.invoke(Method.java:599)
        at com.ibm.wsspi.bootstrap.WSLauncher.launchMain(WSLauncher.java:213)
        at com.ibm.wsspi.bootstrap.WSLauncher.main(WSLauncher.java:93)
        at com.ibm.wsspi.bootstrap.WSLauncher.run(WSLauncher.java:74)
        at org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:78)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:92)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:68)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:400)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:177)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:45)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
        at java.lang.reflect.Method.invoke(Method.java:599)
        at org.eclipse.core.launcher.Main.invokeFramework(Main.java:340)
        at org.eclipse.core.launcher.Main.basicRun(Main.java:282)
        at org.eclipse.core.launcher.Main.run(Main.java:981)
        at com.ibm.wsspi.bootstrap.WSPreLauncher.launchEclipse(WSPreLauncher.java:330)
        at com.ibm.wsspi.bootstrap.WSPreLauncher.main(WSPreLauncher.java:108)
Caused by: java.lang.IllegalStateException: java.lang.NullPointerException
        at com.ibm.ws.util.ImplFactory.loadImplFromClass(ImplFactory.java:354)
        at com.ibm.ws.util.ImplFactory.loadImplFromKey(ImplFactory.java:328)
        at com.ibm.ws.util.ImplFactory.loadImplFromKey(ImplFactory.java:332)
        at com.ibm.ws.wlm.Factory$4.run(Factory.java:141)
        at java.security.AccessController.doPrivileged(AccessController.java:251)
        at com.ibm.ws.wlm.Factory.loadImpl(Factory.java:139)
        at com.ibm.websphere.cluster.topography.DescriptionManagerFactory.(DescriptionManagerFactory.java:50)
        at java.lang.J9VMInternals.initializeImpl(Native Method)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:200)
        at com.ibm.ws.cluster.service.ClusterManagementImpl.(ClusterManagementImpl.java:119)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:45)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:39)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:515)
        at com.ibm.wsspi.cluster.ClusterManagementFactory.(ClusterManagementFactory.java:62)
        at java.lang.J9VMInternals.initializeImpl(Native Method)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:200)
        at com.ibm.ws.cluster.runtime.WLMDiagnosticModule.ffdcDumpDefaultClusterManagement(WLMDiagnosticModule.java:422)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:45)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
        at java.lang.reflect.Method.invoke(Method.java:599)
        at com.ibm.ws.ffdc.DiagnosticModule.getDataForDirective(DiagnosticModule.java:305)
        at com.ibm.ws.ffdc.DiagnosticModule.getDataForDirectives(DiagnosticModule.java:279)
        at com.ibm.ws.ffdc.DiagnosticModule.dumpComponentData(DiagnosticModule.java:144)
        at com.ibm.ws.ffdc.impl.DMAdapter.processDM(DMAdapter.java:123)
        at com.ibm.ws.ffdc.impl.DMAdapter.formatTo(DMAdapter.java:114)
        at com.ibm.ffdc.util.provider.IncidentLogger.writeIncidentTo(IncidentLogger.java:63)
        at com.ibm.ws.ffdc.impl.FfdcProvider.logIncident(FfdcProvider.java:135)
        at com.ibm.ws.ffdc.impl.FfdcProvider.logIncident(FfdcProvider.java:92)
        at com.ibm.ffdc.util.provider.FfdcProvider.log(FfdcProvider.java:232)
        at com.ibm.ws.ffdc.impl.FfdcProvider.log(FfdcProvider.java:100)
        at com.ibm.ffdc.util.provider.IncidentEntry.log(IncidentEntry.java:96)
        at com.ibm.ffdc.util.provider.Ffdc.log(Ffdc.java:90)
        at com.ibm.ws.ffdc.FFDCFilter.processException(FFDCFilter.java:114)
        at com.ibm.ws.cluster.ProcessProperties.(ProcessProperties.java:281)
        at com.ibm.ws.cluster.ProcessProperties.(ProcessProperties.java:234)
        at java.lang.J9VMInternals.initializeImpl(Native Method)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:200)
        at com.ibm.ws.cluster.runtime.ProcessRuntimeImpl.initialize(ProcessRuntimeImpl.java:307)
        ... 31 more
Caused by: java.lang.NullPointerException
        at com.ibm.ws.cluster.WLMCustomPropertyUtility.getBBCallbacksEnableWLMThreads(WLMCustomPropertyUtility.java:384)
        at com.ibm.ws.cluster.propagation.bulletinboard.BBDescriptionManager.(BBDescriptionManager.java:165)
        at java.lang.J9VMInternals.newInstanceImpl(Native Method)
        at java.lang.Class.newInstance(Class.java:1325)
        at com.ibm.ws.util.ImplFactory.loadImplFromClass(ImplFactory.java:349)
        ... 70 more

This should probably mean that your PC's hostname couldn't be resolved.