Different behaviour for Fop Custom Resource Resolver in FOP 2.6 and 2.7+ [Proof of concept]

Abstract

For a library project I've been working, I designed a custom ResourceResolver to load fonts from the class loader instead than from the file system (the default behaviour of FOP).
This library was originally developed linking Apache FOP 2.6.
Recently I wanted to upgrade to Apache FOP 2.7 or 2.8, but when linking the new version of FOP, it seems the custom ResourceResolver is ignored.
This project provide a simple Proof of concept of this different behaviour.
The purpose is to open a bug on Apche FOP JIRA bug track and attach this POC as sample code.

Quickstart

• mvn clean install -P fop26 [Test OK]
• mvn clean install -P fop27 [Test Failed]
• mvn clean install -P fop28 [Test Failed]
  The link to Apache FOP is achivied using a property fop-version overriden in thre different profiles :
• fop26 -> version 2.6
• fop27 -> version 2.7
• fop28 -> version 2.8
  As you can see in the pom.xml file

The project structure

This project consists of basically of :

• ClassLoaderResourceResolver - A custom ResourceResolver loading from the classloader uri starting with "classpath://"
• SampleDocumentGenerator - A sample code customized from the sample code on fop site to use the previous custom ResourceResolver.
• A resource folder with the fonts to be loaded : src/main/resources/font
• The Apache FOP configuration file fop-sample-config.xml
• The Apache FOP sample .fo fop-sample-doc.fo
• A JUnit TestDocGeneration to test the document generation.
• A pom.xml file with three profiles for launching the JUnit with Apache FOP 2.6 (fop26), 2.7 (fop27) and 2.9 (fop28).

Test done

This porject had been tested with the same behaviour with :

• JDK 1.8.0_333 and JDK 11.0.16
• Apache Maven 3.8.6

Some sample build logs are provided :

1. mvn clean install -P fop26 >> sample_build_log/build_log_profile_fop26_jdk8_win.txt 2>&1
2. mvn clean install -P fop27 >> sample_build_log/build_log_profile_fop27_jdk8_win.txt 2>&1
3. mvn clean install -P fop28 >> sample_build_log/build_log_profile_fop28_jdk8_win.txt 2>&1
4. mvn clean install -X -P fop26 >> sample_build_log/build_log_profile_fop26_jdk8_win_debug.txt 2>&1
5. mvn clean install -X -P fop27 >> sample_build_log/build_log_profile_fop27_jdk8_win_debug.txt 2>&1
6. mvn clean install -X -P fop28 >> sample_build_log/build_log_profile_fop28_jdk8_win_debug.txt 2>&1
7. mvn clean install -P fop26 >> sample_build_log/build_log_profile_fop26_jdk11_win.txt 2>&1
8. mvn clean install -P fop27 >> sample_build_log/build_log_profile_fop27_jdk11_win.txt 2>&1
9. mvn clean install -P fop28 >> sample_build_log/build_log_profile_fop28_jdk11_win.txt 2>&1
10. mvn clean install -X -P fop26 >> sample_build_log/build_log_profile_fop26_jdk11_win_debug.txt 2>&1
11. mvn clean install -X -P fop27 >> sample_build_log/build_log_profile_fop27_jdk11_win_debug.txt 2>&1
12. mvn clean install -X -P fop28 >> sample_build_log/build_log_profile_fop28_jdk11_win_debug.txt 2>&1
13. mvn clean install -P fop26 >> sample_build_log/build_log_profile_fop26_jdk8_linux.txt 2>&1
14. mvn clean install -P fop27 >> sample_build_log/build_log_profile_fop27_jdk8_linux.txt 2>&1
15. mvn clean install -P fop28 >> sample_build_log/build_log_profile_fop28_jdk8_linux.txt 2>&1
16. mvn clean install -X -P fop26 >> sample_build_log/build_log_profile_fop26_jdk8_linux_debug.txt 2>&1
17. mvn clean install -X -P fop27 >> sample_build_log/build_log_profile_fop27_jdk8_linux_debug.txt 2>&1
18. mvn clean install -X -P fop28 >> sample_build_log/build_log_profile_fop28_jdk8_linux_debug.txt 2>&1
19. mvn clean install -P fop26 >> sample_build_log/build_log_profile_fop26_jdk11_linux.txt 2>&1
20. mvn clean install -P fop27 >> sample_build_log/build_log_profile_fop27_jdk11_linux.txt 2>&1
21. mvn clean install -P fop28 >> sample_build_log/build_log_profile_fop28_jdk11_linux.txt 2>&1
22. mvn clean install -X -P fop26 >> sample_build_log/build_log_profile_fop26_jdk11_linux_debug.txt 2>&1
23. mvn clean install -X -P fop27 >> sample_build_log/build_log_profile_fop27_jdk11_linux_debug.txt 2>&1
24. mvn clean install -X -P fop28 >> sample_build_log/build_log_profile_fop28_jdk11_linux_debug.txt 2>&1

As can be noted, in the build linked to Apache FOP 2.6 is possible to read the log of the custom ResourceResolver :

2022-11-20 18:29:15.358 [main] INFO  org.fugerit.java.poc.fop.custom.resource.resolver.ClassLoaderResourceResolver - TestClassLoaderResourceResolver.getResource() -> file:/C:/workspace/git/fop-custom-resource-resolver-poc/./target/classes/font/TitilliumWeb-Bold.ttf
2022-11-20 18:29:15.477 [main] INFO  org.fugerit.java.poc.fop.custom.resource.resolver.ClassLoaderResourceResolver - TestClassLoaderResourceResolver.getResource() -> file:/C:/workspace/git/fop-custom-resource-resolver-poc/./target/classes/font/TitilliumWeb-BoldItalic.ttf
2022-11-20 18:29:15.492 [main] INFO  org.fugerit.java.poc.fop.custom.resource.resolver.ClassLoaderResourceResolver - TestClassLoaderResourceResolver.getResource() -> file:/C:/workspace/git/fop-custom-resource-resolver-poc/./target/classes/font/TitilliumWeb-Italic.ttf
2022-11-20 18:29:15.503 [main] INFO  org.fugerit.java.poc.fop.custom.resource.resolver.ClassLoaderResourceResolver - TestClassLoaderResourceResolver.getResource() -> file:/C:/workspace/git/fop-custom-resource-resolver-poc/./target/classes/font/TitilliumWeb-Regular.ttf
2022-11-20 18:29:16.512 [main] INFO  org.fugerit.java.poc.fop.custom.resource.resolver.ClassLoaderResourceResolver - TestClassLoaderResourceResolver.getResource() -> classpath://font/TitilliumWeb-Regular.ttf

The same lines are not present when using the profiles linking to Apache FOP 2.7 and 2.8.

PS: the original library project where this BUG was found is Fugerit Venus.