How to fix "Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass?

Question

I've started a project using java 16 and I'm getting errors in the project all over the place:

An error has occurred. See error log for more details.
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 @6dfcffb5

It looks like the code I have from different version of java is not working in this particular version. Any idea what I need to change maybe in the pojo class. I have only 1 pojo in the application cause it is micro service.

Thanks.

Answer 1

You are using old versions of Spring / Spring Boot that are incompatible with, and do not support Java 16.

According to the Spring Compatibility Matrix , you will need to use Spring 5.3.x or later for Java 16 compatibility.

For Spring-Boot, you need 2.7.1 or later for Java 17 compatibility... according to this Spring And Spring Boot Versions page.

Also note that Java 16 is end-of-life as well. You probably should be using one of the LTS versions of Java; ie Java 8, 11 or 17.

^{(Winding back to an earlier Java LTS would "fix" the Spring compatibility issue, but IMO rolling Spring and Java forward is better. You don't want to be developing a new project on top of base that is already outdated.)}

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The actual problem you are seeing is due to something (probably a Spring Boot custom classloader) accessing an "internal" API. This is blocked (in Java 14 and later) unless you do some tweaking to the way that the JVM is launched. This Q&A gives some background:

• How to solve InaccessibleObjectException ("Unable to make {member} accessible: module {A} does not 'opens {package}' to {B}") on Java 9?

However, the best solution is to use "supported" versions of Java for your selected versions of Spring and Spring Boot.

Answer 2

You can just define the JRE system library by precising the path following the next steps: Project Folder -> Properties -> Java build path -> double clicks on JRE system library and choose your installed JRE, it works for me. And sorry for my bad English