How to configure port for a Spring Boot application

Question

How do I configure the TCP/IP port listened on by a Spring Boot application, so it does not use the default port of 8080.

Answer 1

When spring boot application starts, the embedded server such as Tomcat starts with a default port. The embedded tomcat starts with 8080 port as default. There are many ways to change default server port.

Using Property File (.properties/.yml)

To change server port using property file, we need to configure server.port property.

a. Using application.properties in classpath such as src\main\resources\application.properties

server.port = 8585

The server will start with 8585 port. To get random server port, assign 0 to the property.

server.port = 0

Now spring boot will start the server on a port that is not being used currently by any server in the system.

b. Using application.yml in classpath such as src\main\resources\application.yml.

server:
  port: 8585 

Server will start with 8585 port.

For random port, assign 0.

server:
  port: 0 

Using java Command with --server.port or -Dserver.port

Suppose we have an executable JAR named as my-app.jar, then while starting spring boot application using java command we can use the argument as follows.

Using --server.port

java -jar my-app.jar  --server.port=8585

Using -Dserver.port

java -jar -Dserver.port=8585 my-app.jar

Server will start with 8585 port.

Using java Command with --port or -Dport in Short

To make --server.port and -Dserver.port in short, we can remove server keyword and make it any short keyword such as --port and -Dport. We can use any short keyword. Here we are using port as short keyword. To achieve it we need to configure placeholder in property file as follows.

Using application.properties

server.port=${port:8282}

Using application.yml

server:
   port: ${port:8282}

If we do not pass the port as the argument then by default server will start with 8282. If we want a different port, then we need to pass desired port in argument as follows. Suppose we have an executable JAR named as my-app.jar.

Using --port

java -jar my-app.jar --port=8585 

Using -Dport

java -jar -Dport=8585 my-app.jar 

Server will start with 8585 port.

Using SERVER_PORT with SpringApplication Programmatically

SpringApplication has a method as setDefaultProperties() that is used to change spring boot default properties. Suppose we want to change default port then we need to create a Map and put a port with SERVER_PORT key. Find the example.

MyApplication.java

package com.humoyun;

import java.util.HashMap;
import java.util.Map;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(MyApplication.class);
        Map map = new HashMap<>();
        map.put("SERVER_PORT", "8585");
        application.setDefaultProperties(map);
        application.run(args);
        }     
} 

Spring boot will start the server with 8585 port.