Background methods

Background jobs in JobRunr are just Java 8 lambda's - easy peasy!

Background jobs in JobRunr look like regular method calls. Background jobs can use both instance and static method calls as in the following example.

BackgroundJob.enqueue<EmailSender>(x -> x.send("jobrunr@example.com"));
BackgroundJob.enqueue(() -> System.out.println("Hello, world!"));

Unlike usual method invocations which are run instantly, these methods are in fact Java 8 Functional Interfaces and are executed asynchronously and - depending on the configuration - even outside the current JVM. So the purpose of the method calls above is to collect and serialize the following information:

  • Type name, including package.
  • Method name and its parameter types.
  • Argument values.

Important: all your servers must run the same version of your code! If your webapp server has a newer version with a method signature that is not compatible with the server that processes your background jobs, a NoSuchMethod Exception will be thrown and job processing will fail!
As of JobRunr v1.1.0, the dashboard shows an error if there are jobs which cannot be found.

Serialization is performed by the either Jackson, Gson or Json-B and the resulting JSON, that looks like in the following snippet, is persisted in a StorageProvider making it available for other processing in a different thread or even a different JVM. As we can see everything is passed by value, so heavy data structures will also be serialized and consume a lot of bytes in the RDBMS or NoSQL database.

{
  "lambdaType": "org.jobrunr.jobs.lambdas.JobLambda",
  "className": "java.lang.System",
  "staticFieldName": "out",
  "methodName": "println",
  "jobParameters": [
    {
      "className": "java.lang.String",
      "object": "a test"
    }
  ]
}
the serialized job details

Parameters

You can pass parameters along to your background job methods but these should be kept as small as possible. A parameter must either be:

  • a type of java.lang like String, Integer, …
  • a custom class with a default no argument constructor - this to deserialize it from the StorageProvider

Method visibility

JobRunr only runs methods with public visibility.