How to Package Spring Boot Apps with External Dependencies Using Maven

Introduction

Spring Boot normally builds a fat jar that contains all dependencies and can be started with

java -jar xxx.jar

. In some projects the dependencies are placed outside the jar and the application is launched with

java -Dloader.path=libs -jar xxx.jar

, which makes it easy to replace a single library.

Packaging Method Details

spring-boot-maven-plugin

The official Spring Boot Maven plugin creates the executable jar. To avoid bundling dependencies we set the

layout

to

ZIP

and use the

includes

element to specify a non‑existent jar, effectively excluding all libraries from the fat jar.

maven-assembly-plugin

This plugin allows flexible assembly of the package. In

assembly.xml

we use

include

and

exclude

patterns to copy the required dependencies into a

libs

directory.

Run

mvn clean package

to generate the installation package in

target

.

After unpacking, the

libs

folder contains all external jars.

Startup Method Analysis

The generated jar contains the class

org.springframework.boot.loader.Launcher

, whose

PropertiesLauncher

subclass is used when the layout is

ZIP

. By setting

loader.path

(or the

LOADER_PATH

environment variable) we can add additional classpath locations such as

lib,${HOME}/app/lib

. The command to start the application becomes:

java -jar -Dloader.path=xx1,xx2,public <jarName>.jar

Conclusion

This packaging and launch approach is useful for large modular projects because it allows urgent bug fixes by swapping individual dependency jars without rebuilding the whole application.