Creating a Runnable JAR File in Spring Boot

In the world of Java application development, packaging your application effectively is as crucial as writing good code. If you’re looking to enhance your skills, this article will provide a comprehensive guide on creating a runnable JAR file for your Spring Boot applications. Whether you're a seasoned developer aiming to streamline your deployment process or an intermediate programmer looking to deepen your understanding, you’ll find valuable insights here.

Step-by-Step Guide to Creating a JAR

Creating a runnable JAR file in Spring Boot is a straightforward process, thanks to the framework's inherent support for packaging applications. Here’s a step-by-step guide to help you through the process:

Set Up Your Spring Boot Project: Start by creating a new Spring Boot project. You can use Spring Initializr (https://start.spring.io/) to bootstrap your application quickly. Select the necessary dependencies based on your project requirements.

Add the Maven or Gradle Build File: Depending on your build tool, you need to configure either the pom.xml (for Maven) or the build.gradle (for Gradle) file. Here’s an example for both:

Maven (pom.xml):

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
</dependencies>

Gradle (build.gradle):

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
}

Configure the Build Plugin: For Maven, ensure you have the Spring Boot Maven Plugin configured in your pom.xml:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

For Gradle, you can apply the Spring Boot plugin in your build.gradle:

plugins {
    id 'org.springframework.boot' version '2.5.4'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
}

Build Your Project: To create the runnable JAR file, execute the following command based on your build tool:

After running the command, your JAR file will be located in the target directory (for Maven) or the build/libs directory (for Gradle).

For Maven:

mvn clean package

For Gradle:

./gradlew build

Including Dependencies in Your JAR

One of the major advantages of Spring Boot is its ability to package all the necessary dependencies within the runnable JAR. This ensures that your application will run smoothly across different environments without worrying about missing libraries.

Maven Configuration

In Maven, the Spring Boot Maven Plugin handles the inclusion of dependencies automatically when you build your project. The JAR file generated will contain all the dependencies specified in your pom.xml. To ensure that the dependencies are included correctly, simply follow the previous steps to create your JAR file.

Gradle Configuration

Similarly, for Gradle, the Spring Boot plugin takes care of dependency management. When you build your project, the resulting JAR will include all the necessary dependencies as specified in your build.gradle file. The bootJar task can be used to customize the contents further if needed.

bootJar {
    enabled = true
}

This command ensures that all dependencies, along with your compiled code, are packaged into a single executable JAR.

Running Your JAR from the Command Line

Now that you have created your runnable JAR file, the next step is executing it from the command line. This is an essential skill for developers, especially when deploying applications in production environments.

Navigate to the Directory: Open your command line interface and navigate to the directory where your JAR file is located.

Execute the JAR: Use the following command to run your application:

java -jar your-application-name.jar

Replace your-application-name.jar with the actual name of your JAR file.

Access the Application: If your Spring Boot application is a web application, you can access it by opening a web browser and heading to http://localhost:8080 (or the specified port if you have changed it).

Example Output

After executing the command, you should see logs indicating that the application has started successfully. Here’s a sample of what the console output might look like:

2024-12-25 10:00:00.000  INFO 12345 --- [           main] c.example.DemoApplication                : Starting DemoApplication on hostname with PID 12345
2024-12-25 10:00:00.123  INFO 12345 --- [           main] c.example.DemoApplication                : Started DemoApplication in 3.456 seconds (JVM running for 4.567)

Summary

Creating a runnable JAR file for your Spring Boot applications is a valuable skill that streamlines the deployment process and enhances application portability. By following the steps outlined above, you can effectively package your application along with its dependencies and run it seamlessly from the command line. This process not only simplifies deployment but also ensures that your application behaves consistently across different environments, reducing the chances of runtime errors due to missing libraries.

As you continue to develop your Spring Boot applications, mastering the art of creating runnable JAR files will undoubtedly contribute to your efficiency as a developer. For further details and best practices, be sure to consult the official documentation at Spring Boot Reference Documentation.

Last Update: 28 Dec, 2024