There is no such Java library. You just need to call the CHM compiler in the documentation directory (usually it is placed in C: \ Program Files \ HTML Help Workshop \ hhc.exe).
You might also be interested in the Java-based Javadoc2Help tool :
Javadoc2Help is a Java-based tool for converting javadoc html output generated into Java Help, HTMl Help ( CHM ), and Oracle Help for Java (OHJ).
The package contains the main library lib / Javadoc2Help.jar . You can try to reuse it to generate CHM, but it just calls the compiler.
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