Error when using LogManager (l4j2) with Java 8 (java.lang.reflect.AnnotatedElement cannot be resolved)

问题

I just encountered a strange error when switching the JDK version of a new Project of mine from 7u45 to 8u20. A harmless LogManager declaration at the beginning of my class is being refused with the following error:

The type java.lang.reflect.AnnotatedElement cannot be resolved. It is indirectly referenced from required .class files

This is the code:

public class Class1 {   
    private static Logger log = LogManager.getLogger(Class1.class); 
    ...

Eclipse proposes me to configure the build path, but I have no Idea what to configure because I don't know the underlying problem of that error.

Using the JDK with version 7, everything works fine.

回答1:

When using JDK 8 and an IDE (or any other code processing tool/framework) with its own compiler, like Eclipse, you have to update the tool to a version with Java 8 support, even if you are not using the newer Java 8 features.

The reason is that the compiler must be able to load the newer class files of the JRE in order to compile your software which references these classes.

Sometimes you can get away with an older compiler when it ignores the newer version number of the class files. But some types will confuse older class file parsers as they use new features, notably AnnotatedElement, which now has default methods, and Map.Entry, an interface which now has static methods.

It seems that Eclipse does not make a difference between references for which no class file could be found and class files it failed to read when saying “«classname» cannot be resolved”.

The same applies to all tools and frameworks using ECJ as embedded compiler.

回答2:

If this happens to you in Tomcat running from within Eclipse (question was closed as duplicate and redirects here), go to Preferences → Server → Runtime Environments → Tomcat version → Edit… and make sure the selected JRE matches the Tomcat version. (Maybe you need to install one.)