Comment # 1 on bug 1134000 from Pedro Monreal Gonzalez

Just checked and the JavaScriptEngine.class is there:

jar tvf bsf.jar |grep JavaScriptEngine
Mon May 06 11:32:52 CEST 2019
org/apache/bsf/engines/javascript/JavaScriptEngine.class

I can see two warnings during build:

[javadoc]
/home/abuild/rpmbuild/BUILD/bsf-2.4.0/src/org/apache/bsf/engines/javascript/JavaScriptEngine.java:44:
warning - invalid usage of tag <
[javadoc]
/home/abuild/rpmbuild/BUILD/bsf-2.4.0/src/org/apache/bsf/engines/javascript/JavaScriptEngine.java:44:
warning - invalid usage of tag >

Let me see if these could be related.
Please, post here the error you get with ant or a reproducer.