java.net.MalformedURLException - unknown protocol: jrt

Question

Getting (java.net.MalformedURLException) unknown protocol: jrt error, with suggestion to rebuild the project, in Intellij.

Stack trace -

    Error:Internal error: (java.net.MalformedURLException) unknown protocol: jrt
java.net.MalformedURLException: unknown protocol: jrt
    at java.net.URL.<init>(URL.java:421)
    at java.net.URL.<init>(URL.java:310)
    at java.net.URL.<init>(URL.java:333)
    at com.intellij.compiler.instrumentation.InstrumentationClassFinder.createJDKPlatformUrl(InstrumentationClassFinder.java:61)
    at org.jetbrains.jps.incremental.instrumentation.ClassProcessingBuilder.createInstrumentationClassFinder(ClassProcessingBuilder.java:125)
    at org.jetbrains.jps.incremental.instrumentation.ClassProcessingBuilder.build(ClassProcessingBuilder.java:93)
    at org.jetbrains.jps.incremental.IncProjectBuilder.runModuleLevelBuilders(IncProjectBuilder.java:1246)
    at org.jetbrains.jps.incremental.IncProjectBuilder.runBuildersForChunk(IncProjectBuilder.java:923)
    at org.jetbrains.jps.incremental.IncProjectBuilder.buildTargetsChunk(IncProjectBuilder.java:995)
    at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunkIfAffected(IncProjectBuilder.java:886)
    at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunks(IncProjectBuilder.java:719)
    at org.jetbrains.jps.incremental.IncProjectBuilder.runBuild(IncProjectBuilder.java:371)
    at org.jetbrains.jps.incremental.IncProjectBuilder.build(IncProjectBuilder.java:178)
    at org.jetbrains.jps.cmdline.BuildRunner.runBuild(BuildRunner.java:138)
    at org.jetbrains.jps.cmdline.BuildSession.runBuild(BuildSession.java:308)
    at org.jetbrains.jps.cmdline.BuildSession.run(BuildSession.java:138)
    at org.jetbrains.jps.cmdline.BuildMain$MyMessageHandler.lambda$channelRead0$0(BuildMain.java:235)
    at org.jetbrains.jps.service.impl.SharedThreadPoolImpl.lambda$executeOnPooledThread$0(SharedThreadPoolImpl.java:42)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Please perform full project rebuild (Build | Rebuild Project)

Building full project via mvn is failing due to other artifact issue.

Specs -

java version "1.8.0_201"
IntelliJ IDEA 2017.3.7 (Ultimate Edition)

Answer 1

The JRT namespace has been introduced with Java 9. You cannot access module data with Java 8 and below.

Answer 2

For future users who are confused why the following line appears in the build log:

javac 9 was used to compile java sources

Even though you've configured the bytecode version, compiler etc to 1.8, I'd suggest trying an alternative SDK, like Amazon Coretto ( Project Structure -> Project Settings -> Project -> Project SDK -> Add SDK... ).

This fixed my problem that landed me at this very obscure question.