Packaging and Deployment: JAR, WAR and External Tomcat

Once your application works, you need to run it somewhere else: a server, a container platform, or a company's existing Tomcat installation. Spring Boot supports several ways to package and run an application, and choosing the right one affects startup, operations and upgrades.

This lesson covers every way to run a Spring Boot app during development, building an executable JAR and what is inside it, layered jars and CDS for faster startup, building a WAR for an external servlet container, deploying to external Tomcat 11, running as a Linux service, and the Spring Boot CLI.

Ways to Run During Development

You can run the main method from your IDE; use mvn spring-boot:run or ./gradlew bootRun; run the test-classpath variant with spring-boot:test-run (Testcontainers); or build and run the jar with java -jar. Pass arguments with -Dspring-boot.run.arguments="--server.port=9090" (Maven) or --args (Gradle).

The Executable JAR

mvn package produces a "fat" jar containing your classes (BOOT-INF/classes), all dependencies (BOOT-INF/lib) and a small launcher. It runs anywhere with a compatible JVM: java -jar app.jar. This is the default and recommended packaging — one artifact, embedded Tomcat, the same everywhere from laptop to production container.

Faster Startup: Extracting and CDS

For containers and production, extract the jar with java -Djarmode=tools -jar app.jar extract and run the extracted form; it starts faster and enables Class Data Sharing (CDS) or Java 24+ AOT caches, which can cut startup time significantly. Layered extraction (--layers) also produces efficient Docker image layers, so rebuilding after a code change only uploads your classes, not all dependencies.

Traditional WAR Deployment

If your organisation runs shared Tomcat servers, package a WAR: set <packaging>war</packaging>, extend SpringBootServletInitializer so the container can start Spring, and mark spring-boot-starter-tomcat as provided so the embedded Tomcat is not bundled. Spring Boot 4 requires a Servlet 6.1 container such as Tomcat 11 or Jetty 12.1. The resulting WAR is still executable with java -jar for local testing.

Running in Production

On a Linux server, run the jar as a systemd service with restart policies, a dedicated user and environment-based configuration. On Kubernetes or cloud platforms, build a container image (see the Docker and Buildpacks lessons). In every case, externalise configuration, send logs to stdout or a central system, and use Actuator health endpoints for monitoring.

Spring Boot CLI

The Spring Boot CLI (spring command, installed via SDKMAN or Homebrew) can generate new projects from the command line using Spring Initializr: spring init --dependencies=webmvc,data-jpa my-app. Older versions could also run Groovy scripts directly; that feature was removed, and the CLI is now mainly a project generator and password encoder utility.

Examples

mvn clean package
java -jar target/shop-1.0.0.jar --spring.profiles.active=prod

# What is inside?
jar tf target/shop-1.0.0.jar | more

META-INF/MANIFEST.MF            (Main-Class: org.springframework.boot.loader.launch.JarLauncher)
BOOT-INF/classes/com/webnest/shop/ShopApplication.class
BOOT-INF/classes/application.yml
BOOT-INF/lib/spring-webmvc-7.0.9.jar
BOOT-INF/lib/tomcat-embed-core-11.0.x.jar
BOOT-INF/lib/hibernate-core-7.x.jar
...

# 1. Extract the jar into an efficient layout
java -Djarmode=tools -jar target/shop-1.0.0.jar extract --destination app

# 2. Training run: create a CDS archive, then exit
java -XX:ArchiveClassesAtExit=app/app.jsa -Dspring.context.exit=onRefresh -jar app/shop-1.0.0.jar

# 3. Production runs use the archive
java -XX:SharedArchiveFile=app/app.jsa -jar app/shop-1.0.0.jar

Without CDS: Started ShopApplication in 3.42 seconds
With CDS:    Started ShopApplication in 2.05 seconds

<!-- pom.xml -->
<packaging>war</packaging>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-webmvc</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
        <scope>provided</scope>          <!-- the external Tomcat supplies the server -->
    </dependency>
</dependencies>

// Application class
@SpringBootApplication
public class ShopApplication extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(ShopApplication.class);
    }

    public static void main(String[] args) {
        SpringApplication.run(ShopApplication.class, args);   // still runnable with java -jar
    }
}

# Build and deploy
mvn clean package
copy target\shop.war C:\apache-tomcat-11.0\webapps\
C:\apache-tomcat-11.0\bin\startup.bat

Tomcat log: Deploying web application archive [C:\apache-tomcat-11.0\webapps\shop.war]
... Started ServletInitializer in 4.2 seconds
curl http://localhost:8080/shop/api/products -> 200 OK   (context path = WAR file name)

# /etc/systemd/system/webnest-shop.service
[Unit]
Description=Webnest Shop
After=network.target

[Service]
User=webnest
WorkingDirectory=/opt/webnest-shop
EnvironmentFile=/etc/webnest-shop.env
ExecStart=/usr/bin/java -Xmx512m -jar /opt/webnest-shop/shop.jar
SuccessExitStatus=143
Restart=on-failure

[Install]
WantedBy=multi-user.target

sudo systemctl daemon-reload
sudo systemctl enable --now webnest-shop
journalctl -u webnest-shop -f

● webnest-shop.service - Webnest Shop
     Active: active (running) since Sun 2026-09-27 10:02:11 IST