Java Invoker

by projectriff

The Java Invoker hosts riff functions written in Java.


With the riff CLI you need to provide an archive location with --artifact or -a and a handler specification with --handler. The archive is a jar file, which can be shaded with all required dependencies, or it can be a Spring Boot fat jar (with dependencies nested in BOOT-INF/lib). Simple functions that do not require any dependencies work just fine. The simplest form of the handler is a class name that can be instantiated (with a default constructor). More complex creation scenarios can be handled by giving the handler in the form <bean>[&main=<main>] where

  • <bean> is a class name or bean name, and
  • <main is a Spring @Configuration class to create an application context

If you provide a main parameter you need to include Spring Boot and all the other dependencies of the context in your archive. A Spring Boot jar file does not need an explicit main (there is one in the MANIFEST.MF), but if you supply one it will be used. If the Function has POJO (i.e. not generic JDK classes) as parameter types, then you also need to depend on spring-cloud-function-context (and include that in the archive).


--artifact greeter-1.0.0.jar --handler=functions.Greeter

Example with Spring Boot application:

--artifact greeter-1.0.0.jar --handler=greeter

Example with Spring application context and an explicit main (Note: you need to add quotes around the handler value since it contains an &)

--artifact greeter-1.0.0.jar --handler='greeter&main=functions.FunctionApp'

As long as the dependencies are included in the archive correctly, you can supply a Function with a wide range of input and output types. The input or output types can be plain JDK classes, or POJOs defined in your archive, or Message (from spring-messaging) or Publisher (from reactive-streams) or Flux or Mono (from reactor-core). The Message type will give you access to header metadata in the incoming and outgoing messages. If the input or output is either a Publisher or a Message (or a Publisher<Message>) then both input and output must be in the same form, with possibly different payload types, obviously. POJOs are converted from incoming messages assuming the payload is JSON ans using the GSON library.

How it Works

The invoker is a Spring Boot application with a configuration key function.uri that can be used to point to a java.util.function.Function. Because of the way Spring Boot works you can use an environment variable FUNCTION_URI or a System property function.uri or a command line argument --function.uri (amongst other options). Its value points to a classpath archive, which can be a jar file or a directory, together with parameters:

  • handler: the class name of a Function to execute, or (when main is also used) a bean name of a Function. Can also be a comma, or pipe-separated list of functions, which are composed together at runtime.
  • main: (optional) the class name of a Spring @Configuration that can be used to create a Spring application context, in which the handler is defined.

The jar archive can also be a comma-separated list of archive locations, in case you need to compose things together.


  • A jar file
  • A Spring app (with spring-cloud-function-context) and function specified by bean class
  • A Spring app and function specified by bean name
  • A Spring app split between 2 jar files