GraalVM Native Image compatibility

[Hixon10]

Hello! Thank you for such amazing library.

I wanted to try your library with https://www.graalvm.org/reference-manual/native-image/. However, it does not work out the box. GraalVM is too young project, so it is OK.

So, I understand, that your library does not have any problems, and it is about bugs in GraalVM. However, if you would like to support this platform, you may to fix 2 places:

1. We got NPE in this block of code:

   static {
       InputStream in = null;
       try {
           in = Biweekly.class.getResourceAsStream("biweekly.properties");
           Properties props = new Properties();
           props.load(in);
   }
   ///
   }

The reason is graalvm cannot load Biweekly.class.getResourceAsStream("biweekly.properties").

2. We got ClassNotFoundException because of this code:

   private final transient ResourceBundle messages;
   
   Messages() {
       messages = ResourceBundle.getBundle("biweekly/messages");
   }

So, it is about resources in both cases. When I locally fixed it, biweekly perfectly started, as part of Native image.

[mangstadt]

Hi, thanks for posting!

How did you fix it? Maybe I can add the fix to biweekly.

[Hixon10]

I did a dirty hacks :)

For in = Biweekly.class.getResourceAsStream("biweekly.properties"); I just inlined needed settings.

For Messages I created a class, which contains all biweekly/messages values.

But If you have vision, how these problems may be fixed, I can implement it and create a PR.

[mangstadt]

I am glad that solution worked for you, but I'd rather not move all that stuff into the code. :)

• biweekly.properties: This file is there so that Maven can edit certain information at build time without modifying the code.
• messages.properties: I'd like to keep the messages in this file for organizational reasons.

The fact that GraalVM can't read files from the classpath seems like a major deficiency to me. It is not uncommon for Java code to do that. 😕

[Hixon10]

Yeah, I totally agree with you. I will try to contact with someone connected with GraalVM. Maybe, I did something wrong, or I need to use some flags for native-image tool.

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Upd. https://github.com/oracle/graal/issues/2942