Reduce the size of the standalone jar

[platonai]

To reduce the size of a standalone JAR (also known as a "fat JAR" or "uber JAR") in a Spring Boot or other Java-based application, consider the following strategies:

1. Use Spring Boot Thin Launcher

• Instead of packaging dependencies inside the JAR, use the Thin Launcher (org.springframework.boot.experimental:spring-boot-thin-launcher).
• This allows dependencies to be downloaded at runtime, significantly reducing the initial JAR size.

<dependency>
    <groupId>org.springframework.boot.experimental</groupId>
    <artifactId>spring-boot-thin-launcher</artifactId>
    <version>1.0.28.RELEASE</version>
</dependency>

Run with:

java -jar yourapp.jar

This method requires an internet connection on the first run.

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2. Exclude Unused Dependencies

• Remove unnecessary dependencies from pom.xml (Maven) or build.gradle (Gradle).
• Use dependency analysis tools to detect unused dependencies:

mvn dependency:analyze

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3. Use ProGuard (for Code Shrinking & Obfuscation)

• ProGuard removes unused code and reduces class sizes.

<plugin>
    <groupId>com.github.wvengen</groupId>
    <artifactId>proguard-maven-plugin</artifactId>
    <version>2.3.0</version>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>proguard</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <obfuscate>true</obfuscate>
    </configuration>
</plugin>

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4. Use the spring-boot-maven-plugin Layered JAR Feature

• Exclude development dependencies and optional libraries.

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <layers>
            <enabled>true</enabled>
        </layers>
    </configuration>
</plugin>

Build with:

mvn clean package

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5. Use maven-shade-plugin with Filters

• Exclude unnecessary classes and resources from dependencies.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>shade</goal>
            </goals>
            <configuration>
                <filters>
                    <filter>
                        <artifact>*:*</artifact>
                        <excludes>
                            <exclude>META-INF/*.SF</exclude>
                            <exclude>META-INF/*.DSA</exclude>
                            <exclude>META-INF/*.RSA</exclude>
                        </excludes>
                    </filter>
                </filters>
            </configuration>
        </execution>
    </executions>
</plugin>

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6. Use GraalVM Native Image

• Compile the JAR to a native executable, removing unused classes and reducing size.

native-image -jar yourapp.jar yourapp

This will create a much smaller, optimized binary.

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7. Compress the JAR using Pack200 (Deprecated)

pack200 --gzip yourapp.jar.pack.gz yourapp.jar

This is deprecated in Java 14+, but still works for legacy apps.

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8. Strip Unnecessary Classes & Resources

• Manually inspect the target/dependency folder and remove large unused libraries.
• Use class data sharing (CDS) or jlink (for JDK 9+ modular applications).

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Conclusion

The best approach depends on your needs:

• Minimal download size? → Thin Launcher
• Remove unused classes? → ProGuard or GraalVM
• Remove unnecessary dependencies? → mvn dependency:analyze
• Optimize for performance? → Native Image

Would you like help with a specific method? 🚀