This is a minimalistic Spring Boot application (REST API) used to demonstrate a very simple Maven-based software building process that consists of the following phases:
- compiling Java source code
- running Unit Tests
- creating JAR file
- packing the JAR into OpenJDK-based Docker image
- pushing the image to the Container Image Registry (here Docker Hub)
The application alone returns a dynamically generated UUID (uuid) in a form of a JSON payload:
{ "generatorName":"uuid-1", "uuid":"5e8bbba3-baef-40ea-8cdf-40d81616d0fa" }
The generatorName field contains the name of the backend service that can be injected using Spring properties or a plain environment variable GENERATOR_NAME. You can do it like this:
# JAR
GENERATOR_NAME=uuid-1 exec java -jar basic-spring-1.0-SNAPSHOT.jar pl.mtjakobczyk.apps.reference.App
# Docker container
docker run -d -p 8080:8080 -e "GENERATOR_NAME=uuid-1" --name uuid-1 mtjakobczyk/basic-spring:1.0-SNAPSHOT
The project tree has been initialized using the following command:
mvn archetype:generate -DgroupId=pl.mtjakobczyk.apps.reference -DartifactId=basic-spring -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
.
├── Dockerfile
├── pom.xml
└── src
├── main
│ └── java
│ └── pl
│ └── mtjakobczyk
│ └── apps
│ └── reference
│ ├── App.java
│ ├── controllers
│ │ └── UUIDController.java
│ └── model
│ └── Message.java
└── test
└── java
└── pl
└── mtjakobczyk
└── apps
└── reference
└── AppTest.java
Build process is done through Maven (using Spring Boot and Spotify Dockerfile plugins):
- https://docs.spring.io/spring-boot/docs/current/maven-plugin/usage.html
- https://github.com/spotify/dockerfile-maven
There are two unit tests prepared:
shouldReturnOK()that verifies the REST resource is present under the /uuid path and returns 200 OKshouldReturnGeneratorName()that verifies whether the application reads one of the returned values from environment variable
The unit tests rely on Spring Boot Test Framework (including Spring MVC Test components).
Run tests:
mvn test
Output:
[INFO] Scanning for projects...
[INFO]
[INFO] -------------< pl.mtjakobczyk.apps.reference:basic-spring >-------------
[INFO] Building basic-spring 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ basic-spring ---
...
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ basic-spring ---
...
[INFO] --- maven-resources-plugin:3.1.0:testResources (default-testResources) @ basic-spring ---
...
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ basic-spring ---
...
[INFO] --- maven-surefire-plugin:2.22.2:test (default-test) @ basic-spring ---
[INFO]
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
[INFO] Running pl.mtjakobczyk.apps.reference.AppTest
...
[INFO] Results:
[INFO]
[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.211 s
[INFO] Finished at: 2020-04-15T19:00:51+02:00
[INFO] ------------------------------------------------------------------------
As a matter of fact, packaging is performed in two stages:
- compiled Java classes are collected together and stored in an executable JAR
- Docker Image is created: the JAR is added to a OpenJDK-based image and executed
Maven build part
...
[INFO] --- maven-jar-plugin:3.1.2:jar (default-jar) @ basic-spring ---
[INFO] Building jar: /Users/mjk/git/ref-spring-mvn-basic/service/basic-spring/target/basic-spring-1.0-SNAPSHOT.jar
...
Result: JAR
.
├── Dockerfile
├── pom.xml
├── src
...
└── target
├── basic-spring-1.0-SNAPSHOT.jar
Maven build part
...
[INFO] --- dockerfile-maven-plugin:1.4.13:build (default) @ basic-spring ---
...
[INFO] Image will be built as mtjakobczyk/basic-spring:1.0-SNAPSHOT
[INFO]
[INFO] Step 1/4 : FROM openjdk:8-jdk-alpine
...
[INFO] Step 2/4 : ARG JAR_FILE=target/*.jar
...
[INFO] Step 3/4 : COPY ${JAR_FILE} app.jar
...
[INFO] Step 4/4 : ENTRYPOINT ["java","-jar","/app.jar"]
...
[INFO] Successfully built fe04154972b4
[INFO] Successfully tagged mtjakobczyk/basic-spring:1.0-SNAPSHOT
...
[INFO] Successfully built mtjakobczyk/basic-spring:1.0-SNAPSHOT
...
Result: Docker Image
REPOSITORY TAG IMAGE ID CREATED SIZE
mtjakobczyk/basic-spring 1.0-SNAPSHOT 164f86ca9ada 5 seconds ago 135MB
openjdk 8-jdk-alpine a3562aa0b991 11 months ago 105MB
Pushing image to a remote reigstry consists of two stages:
- tagging the image
- pushing the properly tagged image
We used a custom property in the pom.xml to set the repository name:
<properties>
...
<dockerfile.maven.plugin.repository>mtjakobczyk</dockerfile.maven.plugin.repository>
</properties>
We have to tag the image by using a prefix specific to the container registry (for example registry.hub.docker.com in case of the Docker Hub). We can override the property using the -D parameter:
mvn dockerfile:tag -Ddockerfile.maven.plugin.repository=registry.hub.docker.com/mtjakobczyk
Docker Images:
REPOSITORY TAG IMAGE ID CREATED SIZE
mtjakobczyk/basic-spring 1.0-SNAPSHOT 164f86ca9ada 11 minutes ago 135MB
registry.hub.docker.com/mtjakobczyk/basic-spring 1.0-SNAPSHOT 164f86ca9ada 11 minutes ago 135MB
openjdk 8-jdk-alpine a3562aa0b991 11 months ago 105MB
To push the image we will use the dockerfile:push stage:
mvn dockerfile:push -Ddockerfile.maven.plugin.repository=registry.hub.docker.com/mtjakobczyk \
-Ddockerfile.username=$REGISTRY_USER -Ddockerfile.password="$REGISTRY_PASS"
Maven build part
[INFO] --- dockerfile-maven-plugin:1.4.13:push (default-cli) @ basic-spring ---
[INFO] The push refers to repository [registry.hub.docker.com/mtjakobczyk/basic-spring]
...
[INFO] Image ceaf9e1ebef5: Pushed
