#11 Packing the Spring Boot web app

Summary

This tutorial walks through the process of creating a simple Spring Boot web application and packaging it as a JAR file. The application displays 'Hello World' on a local server and can be built using Maven. The guide covers the steps of generating the project through Spring Initializr, modifying the application to return a response, and packaging the project as a JAR. Finally, it demonstrates how to run the JAR file locally and prepares it for deployment in a container, providing a solid foundation for Docker integration.

Takeaways

• 😀 Start a Spring Boot web application with a simple 'Hello World' setup using Maven and Java.
• 😀 Use the website start.spring.io to easily generate a Spring Boot project with necessary dependencies.
• 😀 Select Maven as the project management tool, Java as the programming language, and define your group ID and artifact ID.
• 😀 Once the project is generated, unzip it and open it in an IDE like IntelliJ IDEA or Eclipse.
• 😀 Create a simple controller (HelloController) in your project to return a 'Hello World' message as a response to a request.
• 😀 Add @RestController annotation to the controller to enable RESTful behavior and return the response as JSON.
• 😀 Run the application locally to ensure it's working correctly by visiting the URL (e.g., http://localhost:8081).
• 😀 If the default port is occupied, change the port number in the application.properties file (e.g., server.port=8081).
• 😀 After confirming the app works locally, create a JAR file using Maven by running 'mvn package' from the terminal.
• 😀 The JAR file is an executable and can be shared or deployed to other environments or containers.
• 😀 Finally, run the generated JAR file using the 'java -jar' command to execute it locally, confirming the app is still functional.

Q & A

How can I create a simple Spring Boot web application?

To create a simple Spring Boot web application, you can use the Spring Initializr (start.spring.io). Select the project type as Maven, language as Java, and choose a Spring Boot version. After filling in the group and artifact ID, click 'Generate' to download a ready-to-use Spring Boot project.

What is the purpose of the 'start.spring.io' website?

'start.spring.io' is a web-based tool provided by Spring to generate Spring Boot project skeletons. It allows you to select configurations like project type, language, Spring Boot version, dependencies, and other settings to quickly set up your project.

What dependencies should I include for a simple 'Hello World' application?

For a basic 'Hello World' application, the default dependencies such as Spring Web should be enough. This will allow you to set up RESTful APIs easily and return responses in JSON format.

How do I define a simple controller in a Spring Boot application?

You can define a controller by creating a new class and annotating it with '@RestController'. Inside the controller, create a method annotated with '@RequestMapping' to handle requests, such as a method that returns 'Hello World' in a string format.

How do I change the default port for a Spring Boot application?

To change the port, modify the 'application.properties' file and add the line 'server.port=8081' (or any other port you prefer). This allows you to avoid conflicts if the default port (8080) is already in use.

How can I package a Spring Boot application into a JAR file?

To package a Spring Boot application into a JAR file, you need to run the 'mvn package' command in the terminal, which will create the JAR file inside the 'target' folder of your project. This JAR file can be distributed and executed on other machines.

How do I run the Spring Boot application from the JAR file?

To run the Spring Boot application from the JAR file, use the command 'java -jar path/to/yourfile.jar'. This will start the application on the port defined in your application properties file.

What if the port I want to use for the application is already occupied?

If the desired port is occupied, you can change the port number by updating the 'server.port' property in the 'application.properties' file to a different number (e.g., 'server.port=8081').

What is the significance of the 'mvn package' command?

'mvn package' is a Maven command that compiles and packages the application into a deployable artifact (such as a JAR or WAR file). This command also ensures that all dependencies and configuration are included in the final package.

How do I deploy a Spring Boot application in a container?

To deploy a Spring Boot application in a container, you need to have the application packaged as a JAR file. Then, you can copy this JAR file into the container, ensuring the container has the necessary environment (like JDK) to run the Java application.