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Building a 22 Megabytes Microservice with Java, Javalin and GraalVM

Johannes Brüderl on September 27, 2018

Oracle's GraalVM allows for ahead-of-time (AOT) compilation of JVM applications. This means, instead of running a JVM process to execute your appli...
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Sven Kanoldt •

I really dislike that there may always be runtime errors that GraalVM can't predict at compile time (correct me if i'm wrong).

I wonder how it is possible after compilation to encounter runtime errors? As I see it the compiler does the static type checks, so at runtime there shouldn't be any surprises. Do I overlook something?

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Johannes Brüderl • • Edited

I quote from GraalVM docs:

SubstrateVM tries to resolve these elements through a static analysis that
detects calls to the reflection API. Where the analysis fails the program
elements reflectively accessed at run time must be specified 
during native image generation in a configuration file [...]

So yeah it's best-effort only, but no guarantee to detect your stuff. Reflection is a hacky side-step to manipulate or create objects etc, so no guarantees. Javac can't give you guarantees about runtime behavior of reflection, so GraalVM can't do it as well.

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Johannes Brüderl •

Well obviously it's horrible but it's most likely not going to ruin your business. I prefer the small Go binary tho.

 
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Johannes Brüderl •

I totally agree with you. The purpose of this post is that even for the people locked into Java development, there might be an option to improve this situation.