Spring Boot – how to run jar?

Spring Boot – How to Run a JAR?

Running a Spring Boot application packaged as a JAR file is a common task for deploying applications. A JAR (Java ARchive) file bundles all the necessary components of a Java application, including compiled code, libraries, and resources, into a single file. This makes it easy to distribute and execute the application on any system with a compatible Java Runtime Environment (JRE). Understanding how to run a Spring Boot JAR is crucial for developers looking to deploy their applications efficiently.

Solution: Running a Spring Boot JAR

1. Building the JAR File

Before running a Spring Boot application as a JAR, you need to build it. This can be done using either Maven or Gradle, which are popular build automation tools in the Java ecosystem.

Using Maven:

Ensure your pom.xml includes the Spring Boot Maven plugin:

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

To build the JAR, execute the following command in your terminal:

mvn clean package

Using Gradle:

Ensure your build.gradle includes the Spring Boot Gradle plugin:

plugins {
    id 'org.springframework.boot' version '3.0.0'
    id 'io.spring.dependency-management' version '1.0.15.RELEASE'
    id 'java'
}

To build the JAR, run:

./gradlew clean build

Output:

Both commands will generate a JAR file in the target (Maven) or build/libs (Gradle) directory.

2. Running the JAR File

Once the JAR file is built, you can run it using the Java command-line tool. This is the simplest way to execute a Spring Boot application.

Command:

java -jar path/to/your-application.jar

Example:

java -jar target/my-spring-boot-app-0.0.1-SNAPSHOT.jar

Output:

The application will start, and you should see logs indicating that the Spring Boot application has launched. You can access the application at http://localhost:8080 by default, assuming it runs a web server.

Advantages:

• Simplicity: Running a JAR file is straightforward and requires only a JRE.
• Portability: The JAR file can be transferred and executed on any system with a compatible JRE.
• Self-contained: All dependencies are included in the JAR, simplifying deployment.

Disadvantages:

• Environment Dependency: Requires a compatible JRE installed on the host machine.
• Limited Configuration: Runtime configurations are limited to what is specified in the application properties or command-line arguments.

3. Running with Additional Options

You can pass additional options to the java -jar command to customize the runtime environment.

Example with JVM Options:

java -Xmx1024m -Xms512m -jar target/my-spring-boot-app-0.0.1-SNAPSHOT.jar

Example with Spring Profiles:

java -jar target/my-spring-boot-app-0.0.1-SNAPSHOT.jar --spring.profiles.active=prod

Output:

These commands allow you to control memory usage and activate specific Spring profiles, respectively.

Advantages:

• Customization: Allows for fine-tuning of the JVM and application behavior.
• Flexibility: Supports various runtime configurations without modifying the code.

Disadvantages:

• Complexity: Requires understanding of JVM options and Spring profiles.
• Error-Prone: Incorrect options can lead to runtime errors or suboptimal performance.

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