2 types of JARs in Maven

 

🎯 There are 2 types of JARs in Maven:

JAR Type	What it contains	Need dependencies separately?
Normal JAR	Only your code (.class files)	✅ Yes, dependencies needed on target machine
Fat JAR / Uber JAR	Your code + all dependencies inside one big JAR	❌ No, everything is bundled

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🔧 Example: Using Normal JAR

When you run:

mvn clean package

It creates:

target/myproject.jar

But this JAR:

• Does not include your dependencies (like Gson, Spring Boot, etc.)

• You will get ClassNotFoundException on the target machine unless:

  • You also copy all 3 dependency JARs

  • Set CLASSPATH or use -cp when running

Example:

bash

java -cp myproject.jar:lib/dependency1.jar:lib/dependency2.jar MainClass

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💥 Better Way: Create a Fat JAR

This includes your code + all dependencies, so you only need one JAR to run anywhere.

✅ Add this Maven Plugin to pom.xml

xml
<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-assembly-plugin</artifactId>
      <version>3.3.0</version>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>com.mitesh.MainApp</mainClass> <!-- change to your main class -->
          </manifest>
        </archive>
      </configuration>
      <executions>
        <execution>
          <id>make-assembly</id>
          <phase>package</phase>
          <goals>
            <goal>single</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

🔨 Then run:

bash

mvn clean package

You’ll get a file like:

bash

target/myproject-jar-with-dependencies.jar

Now just copy this one JAR to any machine and run:

bash

java -jar myproject-jar-with-dependencies.jar

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✅ Summary

Situation	You Need on Target Machine
Built normal JAR with mvn package	❗ All 3 dependencies separately
Built fat JAR with jar-with-dependencies	✅ Just 1 JAR (includes everything)