You can use JD-GUI to decompile jar files and save the whole lot into a source zip file which can then be added to the source search list (via Configure Build Path).
The problem with JD-GUI is that the line numbers are out which makes debugging very difficult, so you need to
- extract the source files from the decompiled source zip file
- Run the script found at https://bushlife.com.au/groups/python/wiki/7539a/Adjust_line_numbers_in_file.html
- zip the generated source back up
- add it as the source path associated with your java file - using Configure Build Path after right clicking on the jar file in your java project.
