Run snakeyaml without java.desktop module

[JaroslavTulach]

I am experimenting with jlink trying to create a small (headless) JDK while still using snakeyaml. I created a small sample program in Demo.java file:

import java.util.Map;
import org.yaml.snakeyaml.Yaml;

public class Demo {

    public static void main(String[] args) {
        Yaml yaml = new Yaml();
        String document = "hello: 25";
        Map map = (Map) yaml.load(document);
        Object h = map.get("hello");
        System.out.println("h: " + h);
    }
}

I compile it and run successfully with JDK21:

$ jdk21/bin/javac -d . -cp snakeyaml-1.28.jar  Demo.java
$ jdk21/bin/java -cp .:snakeyaml-1.28.jar Demo
h: 25

however when I try to run it without java.desktop module, everything fails.

To reproduce

First of all let's build a small JDK via jlink command. I use:

$ jdk21/bin/jlink --output smalljdk --add-modules java.base

this generates a small, restricted JDK in smalljdk directory. Running with regular snakeyaml-1.28 then fails with a linkage error:

$ smalljdk/bin/java -cp .:snakeyaml-1.28.jar Demo
Exception in thread "main" java.lang.NoClassDefFoundError: java/beans/IntrospectionException
        at org.yaml.snakeyaml.constructor.BaseConstructor.getPropertyUtils(BaseConstructor.java:559)
        at org.yaml.snakeyaml.constructor.BaseConstructor.addTypeDescription(BaseConstructor.java:579)
        at org.yaml.snakeyaml.constructor.Constructor.<init>(Constructor.java:103)
        at org.yaml.snakeyaml.constructor.Constructor.<init>(Constructor.java:80)
        at org.yaml.snakeyaml.constructor.Constructor.<init>(Constructor.java:62)
        at org.yaml.snakeyaml.constructor.Constructor.<init>(Constructor.java:48)
        at org.yaml.snakeyaml.Yaml.<init>(Yaml.java:66)
        at Demo.main(Demo.java:7)
Caused by: java.lang.ClassNotFoundException: java.beans.IntrospectionException
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)

the problem is that PropertyUtils class is referencing java.beans classes (part of java.desktop JDK module) and those are not available. One of these classes is even in the signature of the isTransient method and thus the JDK verifier refuses to load the PropertyUtils class.

This PR fixes that by restructuring the code, so only MethodProperty class references the java.beans package. As this class isn't used in BeanAccess.FIELD mode, the following passes with the new snakeyaml JAR file:

snakeyaml$ smalljdk/bin/java -cp .:target/snakeyaml-2.3-SNAPSHOT.jar Demo
h: 25

These changes are not only useful for our project, but for everyone trying to use snakeyaml on a headless JDK without java.desktop. Please consider accepting my refactoring.

[asomov]

synced

[JaroslavTulach]

Can this refactoring be considered for integration? Right now I have to patch your library and it doesn't feel comfortable.

[maslovalex]

Could you move this detection into the PlatformFeatureDetector maybe in something like isIntrospectorAvailable ?

[JaroslavTulach]

Done in 2ca1828. Is that OK?

[asomov]

Can you please expose instruction how to use it ? Is there a link to a wiki ?

It will be delivered in version 2.3
https://bitbucket.org/snakeyaml/snakeyaml/wiki/Changes

[JaroslavTulach]

Thank you for accepting my contribution!