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 the server.port attribute, which is automatically read at runtime by Spring Boot applications.

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

application.properties

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

server.port=9090

EmbeddedServletContainerCustomizer

You can customize the properties of the default servlet container by implementing the EmbeddedServletContainerCustomizer interface as follows:

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.

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 two 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.