'ClassCastException casting a class instance to its own class because it is in an "unnamed module" with gradel and tomcat

There are many similar issues, but none I could find have the class being cast to itself. We are using a dependency on the webp support from this project:

implementation "org.sejda.imageio:webp-imageio:0.1.6"

It works fine if we don't try to change the write params, but if we do like this:

Iterator imageWriters = ImageIO.getImageWritersByFormatName("webp");
ImageWriter writer = (ImageWriter) imageWriters.next();

WebPWriteParam writeParam = new WebPWriteParam(null);
writeParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
writeParam.setCompressionType(writeParam.getCompressionTypes([WebPWriteParam.LOSSY_COMPRESSION]);
writeParam.setCompressionQuality(0.75f);

baos = new ByteArrayOutputStream();
ImageOutputStream ios = ImageIO.createImageOutputStream(baos);
writer.setOutput(ios);
writer.write(null, new IIOImage(img, null, null), writeParam);

We get this strange exception

java.lang.ClassCastException: class com.luciad.imageio.webp.WebPWriteParam cannot be cast to class com.luciad.imageio.webp.WebPWriteParam (com.luciad.imageio.webp.WebPWriteParam is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @34282781; com.luciad.imageio.webp.WebPWriteParam is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @238ad8c) at com.luciad.imageio.webp.WebPWriter.write(WebPWriter.java:67) ~[webp-imageio-0.1.6.jar:?] at com.XXX.business.util.ImageServices$ImageSaver.run(ImageServices.java:874) [rcw-core.jar:?] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) [?:?] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) [?:?] at java.lang.Thread.run(Thread.java:832) [?:?]

I understand class loaders very will, but don't understand how this module concept is not working here. Can you get me pointed in the right direction?

javagradletomcatmoduleclasscastexception


Solution 1:[1]

You have this class twice in the classpath. The error message tries to give you the two sources, but it's not very successful with that.

In general: an object of class A (from classloader/jar C1) is attempted to be typecast to an object of a class with the same name A, but loaded from classloader/jar C2.

Find C1 and C2 and eliminate one of them. Make the class available only once and the problem will go away

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Olaf Kock

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