Inofficial recreation of jd-core 0.7.1
The original JD-GUI https://github.com/java-decompiler/jd-gui includes the jd-core, which exists as additional file https://github.com/java-decompiler/mvn-repo/blob/master/jd/jd-core/0.7.1/jd-core-0.7.1.jar
Like JD-GUI, the JD-Core is licensed under the GPLv3 https://github.com/java-decompiler/jd-gui/blob/master/NOTICE
But unlike JD-GUI, the source code is not published. But the author said, it is allowed to decompile it.
For more info also look at java-decompiler/jd-gui#106
JD-Core was compiled with the eclipse compiler ecj. To see, if it was recreated right, it is helpful to see, if the created binary of the source is binary-identical to the original classes.
So, to compile write
java -jar ecj-3.7.jar -5 -g -cp . [source-file]
with this options, it creates the same binary files.
If it still differ, it have the reason, that I have added the JD-GUI copyright-header in all files. If you delete it and compile it then, then it will be the same binary like the original.
If you become an error in the form "The type java.io.ObjectInputStream cannot be resolved. It is indirectly referenc ed from required .class files", then be sure you don't use Java 8 or newer for compilation with this ecj. Use Java 6 or so.