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(""));
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!

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": "",
  "className": "java.lang.System",
  "staticFieldName": "out",
  "methodName": "println",
  "jobParameters": [
      "className": "java.lang.String",
      "object": "a test"
the serialized job details


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