Example example_spring-hibernate

Part of the full Java 9 Jigsaw modules example suite.

Authors

Originally written by Martin Lehmann, Kristine Schaal and Rüdiger Grammes (cf. original repository).

Migrated for Java Modules support documentation of Apache MavenTM in the course of the Maven Support & Care program by Gerd Aschemann (and other team members) as forked repository. Please add discussions, requirements, bugfixes, etc. to the fork instead of the original.

What is this example about?

  • Running a Spring Boot application with Java9.

  • Using modules

Modules in this example

  • currently only module mod.app, containing the main class (the SpringBootApplication to be startet by Spring Boot)

Module Dependency Graph, created with DepVis

TODO

Example shows …​

A Java 9 application, using Spring and Hibernate, based on Spring Boot 2.x. There are clean-, compile- and run scripts to build and start tests, resp. to run the application.

Currently work in progress. Below see the steps we did so far to get this state:

  • Spring Boot application, with one module (mod.app) containing only the (empty) SpringBootApplication.

  • Compiles and tests ok with Java 11+

  • Runs with Java 11+, via the Maven spring-boot-plugin, or as fat jar via CLI.

Step A: Preparing the project, Bootstrap with Java 8

  1. Configured and downloaded our application with the Spring initializr using Spring Boot 2.0.0 M5, to be run with maven. We included

    • Security for authentication and authorization

    • Jersey for REST services

    • JPA persistence

    • H2 database

Now the application starts with Java 8.

Step B: Prepare for Java 9+ - without modules

  1. To compile and test, the Maven surefire plugin version 2.20.1 is needed. java.xml.bind has to be added as module for test: --add-modules java.xml.bind

  2. We use the spring-boot:run goal to run the application (see run.sh). The argument --add-modules java.xml.bind has to be configured here, too.

  3. We introduced the module mod.app. It contains the SpringBootApplication

  4. To get this compiled, we had to drop jersey (commented out in pom.xml. Otherwise we ran into problems with asm (version conflict with the asm version the compiler needs).

  5. The compiler needs a dependency to asm-6.0. So we had to exclude the asm version from plexus-java (which wants asm-6.0-BETA) and set it explicitely for the compiler.

The application now compiles, tests and runs with Java 9.

Step C: Introducing a Java Module

  1. We converted mod.app`into a module by adding a `module-info.

  2. We then needed to solve more bytecode enhancement issues. Therefore we declared the main class explicitely in the spring-boot:run-plugin. This avoids letting Spring Boot search a main class itself, see https://github.com/spring-projects/spring-boot/issues/10647

  3. Resolving a javassist problem by using the newest version 3.22.0-GA, see https://stackoverflow.com/questions/46132019/java-io-ioexception-invalid-constant-type-19-at-5

  4. Open the module (Adding opens directive to module-info.java).

The SpringBoot Application (module) becomes a top level module, i.e., it is directly loaded as the starting point of the application. It is hardly ever consumed as a module. Therefore, opening the module will do no harm.

TODO: Extend the application with further (sub-) modules.

The application now compiles, tests and runs with Java 11+ and with a module-info.java. Note that both tests and launch are still done on the classpath.

TODOs, LOP, Backlog, Ideas, …​

No software is ready, ever ;-) So here are some ideas left (any other feedback very welcome!):

  • Introduce more modules

  • Run application on the module path

  • Introduce own entities for JPA persistence

  • Introduce own Spring beans

Output and Testing

This example does not use golden master testing because Spring Boot output includes timestamps, port numbers, absolute file paths, and environment-specific information that varies between runs. See the golden master testing section in the main README for more information.