how to use Jacoco when running embedded tomcat8.5

[FEI YANG]

I'm new to use Jacoco to get restapi testing codecoverage of my java webapp project.
The way I run my webapp project:
  1) use gradle to add embedded tomcat dependencies
  2) create a Main function to run tomcat(version8.5) like this: https://devcenter.heroku.com/articles/create-a-java-web-application-using-embedded-tomcat#deploy-to-heroku
  3) use gradle to create a jar file
  4) java -jar xxx.jar in other place(wanna to deploy to aws)
now after run jar file, tomcat start runing and api response is ok

I also wrote sample test code using rest-assure
in this situation how could I use jacoco to coverage code when running the jar file?

I tried add -javaagent like this:
    java -javaagent:jacocoagent.jar=classdumpdir=dump -jar xxx.jar

  when I stopped run using ctrl-c, java class files dumped into dump folder and a jacoco.exec file created but 0 bytes...

please help me..
お願いします。
帮帮忙。。
  

[Evgeny Mandrikov]

JaCoCo creates an empty file at startup to ensure that location is writable.

And all the information is written at the JMV shutdown using https://docs.oracle.com/javase/7/docs/api/java/lang/Runtime.html#addShutdownHook(java.lang.Thread)

I doubt that termination of Tomcat by Ctrl-C results in graceful JVM termination, and thus doubt that hook is executed. So please make sure that you gracefully terminate JVM.