How to Change the Default Port in Spring Boot

Spring Boot applications, by default, run on port 8080. However, there are several ways to change the default port to suit your needs. In this tutorial, we will explore different methods to change the default port in a Spring Boot application.

Prerequisites

• JDK 17 or later
• Maven or Gradle
• IDE (IntelliJ IDEA, Eclipse, etc.)

Step 1: Set Up a Spring Boot Project

1.1 Create a New Spring Boot Project

Use Spring Initializr to create a new project with the following dependencies:

• Spring Web

Download and unzip the project, then open it in your IDE.

Step 2: Change the Default Port Using application.properties

2.1 Modify application.properties

The most straightforward way to change the default port is by modifying the application.properties file. This file is located in the src/main/resources directory.

# src/main/resources/application.properties

server.port=9090

Explanation:

• server.port=9090: Sets the port to 9090. You can change this to any available port number.

Step 3: Change the Default Port Using application.yml

3.1 Modify application.yml

If you prefer using YAML for configuration, you can change the default port by modifying the application.yml file. Create this file in the src/main/resources directory if it doesn't exist.

# src/main/resources/application.yml

server:
  port: 9090

Explanation:

• server.port: 9090: Sets the port to 9090. You can change this to any available port number.

Step 4: Change the Default Port Programmatically

4.1 Create a WebServerFactoryCustomizer Bean

You can also change the default port programmatically by creating a WebServerFactoryCustomizer bean. This approach is useful if you want to dynamically set the port based on some condition or environment variable.

package com.example.demo;

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ServerPortConfig {

    @Bean
    public WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> webServerFactoryCustomizer() {
        return factory -> factory.setPort(9090);
    }
}

Explanation:

• @Configuration: Marks the class as a source of bean definitions.
• WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>: Customizes the web server factory to change the port.
• factory.setPort(9090): Sets the port to 9090. You can change this to any available port number.

Step 5: Change the Default Port Using Command-Line Arguments

5.1 Run the Application with Command-Line Arguments

You can override the default port by passing a command-line argument when running the application. This method is useful for temporary changes or for running the application on different ports in different environments without changing the code or configuration files.

./mvnw spring-boot:run -Dspring-boot.run.arguments=--server.port=9090

Explanation:

• -Dspring-boot.run.arguments=--server.port=9090: Passes the --server.port=9090 argument to the Spring Boot application, overriding the default port. You can change this to any available port number.

Step 6: Change the Default Port Using Environment Variables

6.1 Set Environment Variables

You can use environment variables to change the default port. This approach is useful for containerized applications or environments where you can't easily modify configuration files or command-line arguments.

export SERVER_PORT=9090
./mvnw spring-boot:run

Explanation:

• export SERVER_PORT=9090: Sets the SERVER_PORT environment variable to 9090.
• ./mvnw spring-boot:run: Runs the Spring Boot application, which will use the SERVER_PORT environment variable to set the port. You can change this to any available port number.

Step 7: Create a Simple REST Controller for Testing

To verify that the port has been changed, let's create a simple REST controller.

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

Explanation:

• @RestController: Marks the class as a REST controller.
• @GetMapping("/hello"): Maps GET requests to /hello to the hello method.
• hello(): Returns a simple greeting.

Step 8: Running and Testing the Application

8.1 Run the Application

Run the Spring Boot application using any of the methods mentioned above.

8.2 Test the Application

Open your browser and navigate to http://localhost:9090/hello (assuming you set the port to 9090). You should see the following output:

Hello, World!

Conclusion

In this tutorial, you have learned various methods to change the default port in a Spring Boot application. These methods include modifying application.properties or application.yml, using a WebServerFactoryCustomizer bean, passing command-line arguments, and setting environment variables. This flexibility allows you to configure your application to run on different ports in different environments easily.