How to Slim Down Spring Boot JARs for Faster Deployment

Introduction

SpringBoot is easy to deploy, but when the server is on the public network, the generated JAR can be huge, especially when many dependencies such as Spring Cloud are included, making adjustments painful.

Jar Size Before Slimming

In a typical SpringBoot JAR, most of the disk space is taken by external dependency JARs located in BOOT-INF/lib. An example shows an 18.18 MB JAR where the BOOT-INF/lib directory alone occupies nearly 18 MB.

Solution

Three steps are provided to produce a slimmer JAR that does not embed the dependency libraries.

Step 1: Build the normal JAR and extract the lib folder

Run mvn clean install in the project root, then unzip the resulting JAR and copy the BOOT-INF/lib directory to the target location.

Execute mvn clean install again.

Step 2: Modify pom.xml to exclude the lib folder from the packaged JAR

After adjusting the Maven configuration (shown in the image), rebuild the project with mvn clean install. The new JAR is dramatically smaller because external JARs are no longer bundled.

Step 3: Run the slim JAR together with the extracted lib folder

Place the lib folder from Step 1 and the new JAR in the same directory and start the application with the command shown in the image (using -Dloader.path=lib).

Alternatively, you can use Maven to copy the required JARs.

Notes

Once the project architecture is fixed, the set of JAR dependencies rarely changes; most changes are in business logic.

Future business‑logic updates only require recompiling the lightweight project, greatly improving deployment efficiency.