Eclipse Layout Kernel and version 1.2024.6

[arnaudroques]

Starting from version 1.2024.6, the Eclipse Layout Kernel (ELK) is now integrated into the main library.

This theoretically means that the following diagram should work out-of-the-box:

@startuml
!pragma layout elk
class red
@enduml

While this works perfectly when running the JAR directly, an issue arises when using the webserver, resulting in the following stack trace:

java.lang.IllegalArgumentException: java.lang.reflect.InvocationTargetException
	at net.sourceforge.plantuml.elk.proxy.Reflect.call2(Reflect.java:227)
	at net.sourceforge.plantuml.elk.proxy.core.RecursiveGraphLayoutEngine.layout(RecursiveGraphLayoutEngine.java:13)
	at net.sourceforge.plantuml.elk.CucaDiagramFileMakerElk.createFile(CucaDiagramFileMakerElk.java:330)
	at net.atmp.CucaDiagram.exportDiagramInternal(CucaDiagram.java:437)
	at net.sourceforge.plantuml.classdiagram.ClassDiagram.exportDiagramInternal(ClassDiagram.java:84)
	at net.sourceforge.plantuml.UmlDiagram.exportDiagramNow(UmlDiagram.java:138)
	at net.sourceforge.plantuml.AbstractPSystem.exportDiagram(AbstractPSystem.java:207)
	at net.sourceforge.plantuml.servlet.DiagramResponse.sendDiagram(DiagramResponse.java:204)
	at net.sourceforge.plantuml.servlet.UmlDiagramService.doDiagramResponse(UmlDiagramService.java:100)
	at net.sourceforge.plantuml.servlet.UmlDiagramService.doGet(UmlDiagramService.java:62)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:500)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:587)
	at org.eclipse.jetty.servlet.ServletHolder$NotAsync.service(ServletHolder.java:1410)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:764)
	at org.eclipse.jetty.servlet.ServletHandler$ChainEnd.doFilter(ServletHandler.java:1665)
	at org.eclipse.jetty.websocket.servlet.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:170)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:527)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:131)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:598)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:223)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1570)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:221)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1381)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:176)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:484)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1543)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:174)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1303)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:129)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:149)
	at org.eclipse.jetty.server.handler.HandlerList.handle(HandlerList.java:51)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at org.eclipse.jetty.server.Server.handle(Server.java:563)
	at org.eclipse.jetty.server.HttpChannel$RequestDispatchable.dispatch(HttpChannel.java:1598)
	at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:753)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:501)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:287)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:314)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.run(AdaptiveExecutionStrategy.java:199)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:411)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:969)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.doRunJob(QueuedThreadPool.java:1194)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1149)
	at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at net.sourceforge.plantuml.elk.proxy.Reflect.call2(Reflect.java:224)
	... 51 more
Caused by: org.eclipse.elk.core.UnsupportedConfigurationException: Unable to load default layout algorithm org.eclipse.elk.layered for unconfigured node Root Node
	at org.eclipse.elk.core.data.LayoutAlgorithmResolver.resolveAlgorithm(LayoutAlgorithmResolver.java:61)
	at org.eclipse.elk.core.data.LayoutAlgorithmResolver.visit(LayoutAlgorithmResolver.java:28)
	at org.eclipse.elk.core.util.ElkUtil.applyVisitors(ElkUtil.java:1089)
	at org.eclipse.elk.core.RecursiveGraphLayoutEngine.layout(RecursiveGraphLayoutEngine.java:100)
	at org.eclipse.elk.core.RecursiveGraphLayoutEngine.layout(RecursiveGraphLayoutEngine.java:80)
	... 56 more

Any insights on what might be causing this issue?

[StephanPirnbaum]

I don't have a solution (yet), but found the same issue with the plantuml plugin for IntelliJ --> esteinberg/plantuml4idea#359 (comment)

While investigating the issue, I stumbled across this post in the plantuml forum --> https://forum.plantuml.net/18998/elk-dont-work

And I can confirm what they wrote (for the IntelliJ plugin atleast). When doing a sequence diagram with ELK, it works, when doing a simple class diagram, it doesn't.

As I believe this has nothing to do with the plantuml-server nor with the IntelliJ plugin, I'll open an issue in the main repository.

[arnaudroques]

When doing a sequence diagram with ELK, it works, when doing a simple class diagram, it doesn't.

This happens because ELK isn't used for sequence diagrams—we have our own internal layout engine for those.

Caused by: org.eclipse.elk.core.UnsupportedConfigurationException: Unable to load default layout algorithm org.eclipse.elk.layered for unconfigured node Root Node
	at org.eclipse.elk.core.data.LayoutAlgorithmResolver.resolveAlgorithm(LayoutAlgorithmResolver.java:61)
	at org.eclipse.elk.core.data.LayoutAlgorithmResolver.visit(LayoutAlgorithmResolver.java:28)
	at org.eclipse.elk.core.util.ElkUtil.applyVisitors(ElkUtil.java:1089)
	at org.eclipse.elk.core.RecursiveGraphLayoutEngine.layout(RecursiveGraphLayoutEngine.java:100)
	at org.eclipse.elk.core.RecursiveGraphLayoutEngine.layout(RecursiveGraphLayoutEngine.java:80)
	... 56 more

Unfortunately, we're stuck with this error message. I think only some people from the ELK team could explain what's happening, as everything works fine when we use the JAR directly. Maybe you can give them a call :-)

[arnaudroques]

On second thought, we're trying this: 185d5f1
Not sure if it will help, but we'll see! :-)

[StephanPirnbaum]

Imho, adding the dependencies will not work as otherwise, you'd get a ClassNotFoundException. In the stacktrace you see elk core as part of it.

Before PlantUML contained Elk, you did get a ClassNotFoundException in the IntelliJ plugin which was replaced by the InvocationTargetException when I added the Elk dependencies manually to it. I, however, don't know for sure for the server.

But thanks for the info with the sequence diagram. I didn't know that.