Skip to main content

🗓️ 28082025 1056
📎

jar_types

🎯 Core Concept​

  • Plain JAR = Library (shareable code)
  • Boot JAR = Application (runnable program)

📊 Key Differences​

Plain JARBoot JAR
SizeSmall (~KB-MB)Large (50-500MB)
ContentsYour classes onlyYour classes + ALL dependencies
Executable❌ No✅ java -jar app.jar
As Dependency✅ Yes❌ No (nested structure)

🔧 Maven Solution (Multi-module projects)​

<!-- Generate BOTH plain + boot JARs -->
<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <executions>
        <execution>
            <goals><goal>repackage</goal></goals>
            <configuration>
                <classifier>boot</classifier>  <!-- 🔑 Magic line -->
            </configuration>
        </execution>
    </executions>
</plugin>

Result:

  • app-1.0.jar → Plain JAR (for dependencies)
  • app-1.0-boot.jar → Boot JAR (for execution)

⚡ Quick Mental Model​

  • Plain JAR = 📚 Library book (others can reference)
  • Boot JAR = 🎬 Complete movie (self-contained entertainment)

🚨 Common Problem​

Error: unable to resolve class in multi-module projects
Cause: Spring Boot only generates boot JARs by default
Fix: Add <classifier>boot</classifier> to generate both types

References