🗓️ 28082025 1056

JAR TYPES

🎯 Core Concept

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

📊 Key Differences

	Plain JAR	Boot JAR
Size	Small (~KB-MB)	Large (50-500MB)
Contents	Your classes only	Your 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

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References