Hi Spring Boot Experts –
I am trying to create a spring boot uber jar that needs to be deployed to a apache storm cluster. But, the catch is that Storm is expecting all the class files in the root of the jar while the packaged app files are under "BOOT-INF/classes" when packaged using the "spring-boot-maven-plugin".
Is there a way I can have my app classes packaged directly under the root instead of "BOOT-INF/classes"?
I tried using the "maven-assembly-plugin" with the "spring-boot-maven-plugin" as shown below which creates the Uber jar with all the class files from the dependency jars packaged at the root of the uber jar, but the app classes are still at BOOT-INF/classes.
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.apache.storm</groupId>
<artifactId>storm-core</artifactId>
</exclude>
</excludes>
<requiresUnpack>
<dependency>
<groupId>com.myorg</groupId>
<artifactId>my-app-artifact</artifactId> <!-- This does not help! :( -->
</dependency>
</requiresUnpack>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.4</version>
<configuration>
<appendAssemblyId>false</appendAssemblyId>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
Best Answer
So, for my future self or for anyone who is trying to find an answer for a similar question. Here are the different things that I realized during my research for this -
So, to make a Spring Boot jar work on the storm cluster while behaving as Spring Boot - we would need to create a copy of all the classes from BOOT-INF/classes to the root of the jar file.
Is this possible? and the answer is yes.
Using the approach describe here, I was able to create a Spring Boot jar with the BOOT-INF/classes copied to the root of the Spring Boot jar. This approach requires ant build.xml, ivy settings and an ivy.xml as shown below. (disclaimer: config tested only till packaging on not on the storm cluster)
Since we are able to create a Spring Boot Jar hacked with classes at the root -
Should we do it? NO.
Here are the reasons -
Spring strongly advises not taking this approach to not end up with unwanted class overwrite and class versioning issues for classes with same names across jar files and with different versions.
Spring Boot Jar packaging is not a format intended for using as a dependency jar. Read the first line here. Hence for dependency use cases, you need to stick with your plain old java modules. Spring Boot is for more of standalone executables or for deployment on containers like tomcat.
Good luck!
build.xml
ivysettings.xml
ivy.xml