The webhook will post json representation of OneDev event to your url. For instance, for code push event, below object will be posted as json:

https://code.onedev.io/projects/160/blob/main/server-core/src/main/java/io/onedev/server/event/RefUpdated.java?position=source-11.14-11.24-1

And for build event, below object will be posted:

https://code.onedev.io/projects/160/blob/main/server-core/src/main/java/io/onedev/server/event/build/BuildEvent.java?position=source-13.14-13.24-1

Thanks for your answer. I have tested it and I got this response,

{
  "@class" : "io.onedev.server.event.RefUpdated",
  "user" : null,
  "date" : "2022-03-24T06:07:35.457+00:00",
  "project" : {
    "id" : 94,
    "name" : "tuoyang-backend-hs-pc",
    "description" : "XXXXX",
    "createDate" : "2022-03-20T13:50:37.000+00:00",
    "updateDate" : "2022-03-24T06:05:01.530+00:00",
    "codeManagement" : true,
    "issueManagement" : true,
    "serviceDeskName" : "<$NullServiceDesk$>6725a5ef-5f67-4cc5-a187-5a846302388d",
    "forkedFromId" : null,
    "parentId" : 49,
    "defaultRoleId" : null
  },
  "refName" : "refs/heads/develop",
  "oldCommitId" : "03386d003ab16d9afc498e3b54bad954b7c437a7",
  "newCommitId" : "8ad3ab800e87b4aab87a11c6c0e5e109af1d3a3c"
}

I have some questions,1. Why the user is null, 2. Can I get the latest commit message?

User is null as this type of event is not triggered by user explicitly on web UI. To get the commit message, you may get the commit object via RESTful api:

https://code.onedev.io/help/api/io.onedev.server.rest.RepositoryResource/getCommit