This is both a blessing and a curse. Some answers and docs are decades old and although still work, are not “fashionable java” (think streams, for instance).
Has that gotten better recently? It's been years since I've toyed with it.
A lot of cruft is still there; Date, File, InputStream/OutputStream, sun.misc.Unsafe, and the entire legacy reflection API are the bunch that stick out to me. Newer releases are actively mentioning their legacy status in documentation, and there are certainly JEPs to remove them or make them opt-in/opt-out.
If you look at OpenJDK internals, or even the foreign function/memory APIs as described in the article, it looks almost nothing like the Java I learned on and wrote for several years. Most of the Panama API is piggybacking on additions to the language made post-JDK9 or so, such as MethodHandle, VarHandle and @PolymorphicSignature methods. So I'd say the language and runtime is evolving nicely, even under the thumb of Oracle.
I think I missed the announcement of those being "legacy" APIs? They show up all over the place including in libraries, what is the replacement?
Did I miss something somewhere ? java.lang.reflect is still the standard way of doing Reflection.
In terms of complexity, it really depends on what you want to do. Using a powerful framework like Spring can entail some config (albeit much less than it used to). Also you would typically use a build tool like maven or gradle to manage dependencies, build artifacts, etc.. Especially maven can be a little arcane. But another major upside of the aforementioned maturity is that there are reams of docs and stackoverflow answers which will almost certainly contain solutions for any problems you might encounter.