By default, Spring Boot applications run on an embedded Tomcat via port 8080. In order to change the default port, you just need to modify server.port attribute which is automatically read at runtime by Spring Boot applications.

In this tutorial, we provide the common ways of modifying server.port attribute.

1- application.properties

Create application.properties file under src/main/resources and define server.port attribute inside it:

application.properties

server.port=9090

2- EmbeddedServletContainerCustomizer

You can customize the properties of the default servlet container through implementing the  EmbeddedServletContainerCustomizer interface as the following:

package com.programmer.gate;
 
import org.springframework.boot.context.embedded.ConfigurableEmbeddedServletContainer;
import org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizer;
 
public class CustomContainer implements EmbeddedServletContainerCustomizer {
 @Override
 public void customize(ConfigurableEmbeddedServletContainer container) {
 container.setPort(9090);
 }
}

The port defined inside the CustomContainer always overrides the value defined inside application.properties.

3- Command line

The third way is to set the port explicitly when starting up the application through the command line, you can do this in 2 different ways:

• java -Dserver.port=9090 -jar executable.jar
• java -jar executable.jar –server.port=9090

The port defined using this way overrides any other ports defined through other ways.