Across & Spring Boot auto-configuration support

You can use @AcrossApplication to execute as a Spring Boot application and use auto-configuration of your application infrastructure. However not all auto-configuration classes are supported in an Across application.

This document explains why that is and how developers can provide compatibility adapters for existing configurations.

Spring Boot auto-configuration compatibility

Most Spring related libraries are fine-tuned to easily work in a single Spring ApplicationContext. This is also very much the case with the default Spring Boot auto-configuration classes.

An Across application has a more complex ApplicationContext hierarchy:

  • every module has its own ApplicationContext: module level

  • the Across context has single ApplicationContext that is the parent of all modules: Across context level

  • in case of executing as Spring Boot (using @AcrossApplication) there is an additional ApplicationContext that is the parent of the Across context: application (infrastructure) level

There is a difference between the application and the application module. The latter is a single module in the Across context. Please read the chapter on Across application project structure if you do not clearly understand this difference.

Because of the hierarchy, visibility, dependencies and creation order of beans are more important. This helps you define clearly dependant modules, but it adds additional complexity compared to a single ApplicationContext application.

Default Spring Boot auto-configuration classes only work in the top-level ApplicationContext, the application level. Often we require them to activate behaviour in modules, as such they usually do not work out-of-the-box and need to be adapted.

Across provides some ways to add auto-configuration compatibility for Across applications. This can allow developers to use the same starters and libraries in an Across application, often with no (or very little) difference.

Not every library or auto-configuration works as easily in an Across application. The Across auto-configure artifact contains compatibility configuration for common starters and libraries, to ease the transition for developers.

Across auto-configure project

The Across auto-configure project adds Across support for many commonly used Spring Boot starters. The adapters are available in the separate across-autoconfigure artifact. This artifact is part of the Across Platform and usually added to any Across application.

<dependency>
    <groupId>com.foreach.across</groupId>
    <artifactId>across-autoconfigure</artifactId>
</dependency>

The chapter on supported starters and libraries gives an overview of what is supported by the auto-configure artifact.

Across & Spring Boot Adding auto-configuration support »