Dynamic Loading of JAR Files in Spring Boot Applications

The article introduces the concept of dynamically loading JAR files in Spring Boot applications, explaining why runtime JAR loading improves modularity, hot‑plug capability, and development efficiency.

It defines dynamic JAR loading, describing its role in enabling flexible component updates without restarting the application.

Using Spring Boot's built‑in SpringBootClassLoader (which extends URLClassLoader ), the guide shows how to create a JAR (e.g., example.jar ) and load it at runtime, with a concrete code snippet:

jar cfm example.jar com/example/demo/MainClass.class -C src/main/java .

import org.springframework.boot.loader.JarLauncher;
import org.springframework.boot.loader.Launcher;
public class DynamicLoading {
    public static void main(String[] args) throws Exception {
        Launcher launcher = new JarLauncher();
        launcher.launch(args, new String[]{"com.example.demo.MainClass"});
    }
}

The article then presents an alternative approach using the third‑party osgi-resource-locator library. It details adding the Maven dependency, creating a JAR with the required META-INF/services/org.osgi.resource.locator.ResourceLocator file, and loading the JAR via the ResourceLocator interface, illustrated with the following snippets:

<dependencies>
    <!-- osgi-resource-locator dependency -->
    <dependency>
        <groupId>org.osgi</groupId>
        <artifactId>org.osgi.resource.locator</artifactId>
        <version>1.0.1</version>
    </dependency>
</dependencies>

import org.osgi.resource.locator.Resource;
import org.osgi.resource.locator.ResourceContent;
import org.osgi.resource.locator.ResourceException;
import org.osgi.resource.locator.ResourceLocator;
public class DynamicLoading {
    public static void main(String[] args) throws Exception {
        ResourceLocator resourceLocator = new ResourceLocator() {
            @Override
            public ResourceContent getResourceContent(Resource resource) throws ResourceException {
                return new ResourceContent() {
                    @Override
                    public InputStream getInputStream() throws IOException {
                        return new FileInputStream("example.jar");
                    }
                    @Override
                    public String getURI() {
                        return "jar:file:/path/to/example.jar!/";
                    }
                };
            }
        };
            // Load the JAR
            Resource resource = resourceLocator.locate("org.osgi.resource.locator", "()");
            if (resource != null) {
                Class
clazz = resource.loadClass("com.example.demo.MainClass");
                clazz.newInstance();
            }
    }
}

In conclusion, the article demonstrates that developers can enhance Spring Boot applications by leveraging either the native SpringBootClassLoader or OSGi‑based solutions to load JARs dynamically, thereby increasing system flexibility and extensibility.