Spring Boot Container with JLink

Here's how I computed the modules for jlink:

$ CP=`java -jar target/sample-docker-microservice-1.0-SNAPSHOT.jar --thin.classpath`
$ MODS=`jdeps --ignore-missing-deps --multi-release 17 --print-module-deps --class-path ${CP} target/classes/pl/piomin/microservices/person/Application.class`

Then you can create a jlink binary distro like this:

$ jlink --compress=2 --module-path ${JAVA_HOME}/jmods --add-modules "${MODS}" --no-header-files --no-man-pages --output target/thin

Run the app:

$ ./target/thin/bin/java -cp ${CP} pl.piomin.microservices.person.Application

The Dockerfile in the root of the project does the last bit for you and takes a step further by also setting up App CDS.

The docker image is about 160MB:

Cmp   Size  Command                                                                       
    5.6 MB  FROM 695e5153d90d6a4                                                          
     65 MB  COPY /springboot-runtime /opt/jdk # buildkit                                  
     31 MB  COPY /opt/app/repository /opt/app/repository # buildkit                       
     13 kB  COPY /opt/app/app.jar /opt/app # buildkit                                     
    691 kB  COPY /opt/app/app.classlist /opt/app # buildkit                               
    4.1 kB  COPY /opt/app/classpath /opt/app # buildkit                                   
     69 MB  RUN /bin/sh -c java -Xshare:dump -XX:SharedClassListFile=/opt/app...

The biggest chunks in there are:

• Java runtime, 65MB
• Jar files, 31MB (could probably be slimmed down)
• CDS cache, 69MB

(Original idea by @piomin.)

Modules Used

The MODS generated above from jdeps looks like quite a long list:

java.base,java.desktop,java.instrument,java.management,java.naming,java.prefs,java.rmi,java.scripting,java.sql,jdk.httpserver,jdk.jfr,jdk.unsupported

Spring 6 will get rid of java.desktop (the Java Beans dependency). You can slim that down to

java.base,java.desktop

and get an app to run with warnings (because java.management is missing).

Older Notes

Before Spring Boot 2.7 without java.naming you get errors in Spring:

Caused by: java.lang.NoClassDefFoundError: javax/naming/NamingException
        at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.<init>(CommonAnnotationBeanPostProcessor.java:177) ~[spring-context-5.3.10.jar:5.3.10]

The pom.xml excludes snakeyaml. If you don't do that you also need java.logging.