dumper.java code is copied from Reversing an obfuscated java malware by Extreme Coders

Uploaded the jar file generated using following cmds:

javac dumper.java
jar cmf MANIFEST.MF dumper.jar dumper.class transformer.class

To dump the class file of malware.jar:

java -javaagent:dumper.jar -jar malware.jar

Important note: Another important point is there must be a new line at the end of the MANIFEST file. Otherwise, the last header is ignored.