I’m facing an issue with my Java Spring Boot application where I dynamically load plugins using ServiceLoader. The application works perfectly in my local development environment (IntelliJ IDE), but when I build the JAR files and run them, I encounter the following error:

Caused by: java.util.ServiceConfigurationError: com.example.plugins.Plugin: com.example.plugins.vendor.VendorPluginManager not a subtype
    at java.base/java.util.ServiceLoader.fail(ServiceLoader.java:593)
    at java.base/java.util.ServiceLoader$LazyClassPathLookupIterator.hasNextService(ServiceLoader.java:1244)
    at java.base/java.util.ServiceLoader$LazyClassPathLookupIterator.hasNext(ServiceLoader.java:1273)
    at java.base/java.util.ServiceLoader$2.hasNext(ServiceLoader.java:1309)
    at java.base/java.util.ServiceLoader$3.hasNext(ServiceLoader.java:1393)
    at com.example.global.plugins.PluginLoader.loadPlugins(PluginLoader.java:39)
    at com.example.global.plugins.PluginConfig.plugins(PluginConfig.java:22)
    at com.example.global.plugins.PluginConfig$$SpringCGLIB$$0.CGLIB$plugins$0(<generated>)
    at com.example.global.plugins.PluginConfig$$SpringCGLIB$$FastClass$$1.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:258)
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331)
    at com.example.global.plugins.PluginConfig$$SpringCGLIB$$0.plugins(<generated>)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:139)
    ... 56 common frames omitted

Project Structure

server (spring-boot)
  ├── src
  ├── build.gradle
  ├── plugin-module
  │   ├── build.gradle
  │   ├── src
  └── common-plugin
      ├── build.gradle
      ├── src

plugins
  └── plugin-module-1.0.0.jar (built-plugin file)

Common Plugin Interface

In common-plugin:

package com.example.plugins;

public interface Plugin {
    void initialize();
    String getName();
}

Plugin Implementation

In plugin-module:

package com.example.plugins.vendor;

import com.example.plugins.Plugin;

public class VendorPluginManager implements Plugin {
    @Override
    public void initialize() {
        System.out.println("VendorPluginManager initialized!");
    }

    @Override
    public String getName() {
        return "vendorPlugin";
    }

    // Additional methods...
}

META-INF/services/com.example.plugins.Plugin

com.example.plugins.vendor.VendorPluginManager

PluginLoader

In server:

package com.example.global.plugins;

import com.example.plugins.Plugin;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;
import java.util.ServiceLoader;

@Component
public class PluginLoader {

    @Value("${plugins.path:./plugins}")
    private String pluginsPath;

    public List<Plugin> loadPlugins() throws Exception {
        File dir = new File(pluginsPath);
        File[] files = dir.listFiles((d, name) -> name.endsWith(".jar"));

        List<Plugin> plugins = new ArrayList<>();
        if (files != null) {
            for (File file : files) {
                URL[] urls = {file.toURI().toURL()};
                try (URLClassLoader classLoader = new URLClassLoader(urls)) {
                    ServiceLoader<Plugin> loader = ServiceLoader.load(Plugin.class, classLoader);
                    for (Plugin plugin : loader) {
                        plugins.add(plugin);
                    }
                }
            }
        }
        return plugins;
    }
}

Gradle Build Files

server/build.gradle:

plugins {
    id 'java'
    id 'org.springframework.boot' version '2.6.3'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
}

group = 'com.example'
version = '1.0.0'

repositories {
    mavenCentral()
}

dependencies {
    implementation project(':common-plugin')
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'org.springframework.boot:spring-boot-starter-jdbc'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

bootJar {
    mainClassName = 'com.example.Application'
}

plugin-module/build.gradle:

plugins {
    id 'java'
    id 'com.github.johnrengelman.shadow' version '7.1.2'
}

group = 'com.example'
version = '1.0.0'

repositories {
    mavenCentral()
}

dependencies {
    compileOnly project(':common-plugin')
    implementation 'com.some.library:example:1.0.0'
}

Issue

It seems like the VendorPluginManager class is not being recognized as a subtype of Plugin when I build the JAR files and run them.

Why am I getting this ServiceConfigurationError in deployment?
What steps can I take to resolve this issue?
Any help or suggestions would be greatly appreciated!