Eclipse 2021-06: ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module

Question

Upgrading to the last Eclipse version, now I am getting the following error:

Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @5d01b0d8

I tried changing JDK under preferences with no luck.

Answer 1

Thanks, @howlger it was Lombok plug-in when using JDK 16. That tweet gave me the reasons: https://github.com/projectlombok/lombok/issues/2810

A workaround :

• Use Java 15 to start Eclipse or
• add --illegal-access=warn and --add-opens java.base/java.lang=ALL-UNNAMED to your eclipse.ini
• or install a pre-built version (1.18.21)

In my situation I had to change eclipse.ini VM path:

-vm
C:\bin\jdk-15.0.2\bin

Answer 2

An easy way is to change the Java Version used to run Eclipse. There for you have to change the eclipse.ini.

1. Set the vm location at the start of the file to a prior Java 16 JDK e.g. JDK 14
2. Under MacOSX eclipse.ini is typically located in /Applications/Eclipse.app/Contents/Eclipse/
3. The reason is an incompatibility of the lombock plugin

---

This a working example of the eclipse.ini file:

-vm
/Library/Java/JavaVirtualMachines/jdk-14.0.2.jdk/Contents/Home/bin/java
-startup
../Eclipse/plugins/org.eclipse.equinox.launcher_1.6.200.v20210416-2027.jar
--launcher.library
../Eclipse/plugins/org.eclipse.equinox.launcher.cocoa.macosx.x86_64_1.2.200.v20210527-0259
-product
org.eclipse.epp.package.java.product
-showsplash
org.eclipse.epp.package.common
--launcher.defaultAction
openFile
--launcher.defaultAction
openFile
--launcher.appendVmargs
-vmargs
-javaagent:/Applications/Eclipse.app/Contents/Eclipse/lombok.jar
-Dosgi.requiredJavaVersion=11
[email protected]/eclipse-workspace
-Dsun.java.command=Eclipse
-XX:+UseG1GC
-XX:+UseStringDeduplication
--add-modules=ALL-SYSTEM
-Dorg.eclipse.swt.internal.carbon.smallFonts
-Dosgi.dataAreaRequiresExplicitInit=true
-Dorg.eclipse.swt.graphics.Resource.reportNonDisposed=true
-Xms256m
-Xmx2048m
-Xdock:icon=../Resources/Eclipse.icns
-XstartOnFirstThread