where is port 8080 defined in spring cloud app? - spring

Question

I have been doing a line by line study of the code in this spring cloud app on github after downloading and installing it on my devbox. When you type http://localhost:8080 in your web browser, the content from the ui app loads, and is able to interact with the content from the authserver and resource apps.
Port 9999 is defined for the authserver app, both in the ui app's zuul route definitions, and also in the authserver app's application.properties.
Similarly, port 9000 is defined for the resource app, both in the ui app's route definitions, and also in the resource app's application.properties.
But I cannot find any reference to port 8080, even after reviewing every line of code in the three apps and also doing a Ctrl-H to do full text search of the entire eclipse workspace for the word 8080.
So how does the ui app know to serve its client content on port 8080?

Answer 1

The UI module has the following Spring Boot dependency:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
That dependency has its own dependencies as seen here:
Spring Boot Starter Web POM.xml
This includes the Spring Boot's Tomcat Starter:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</dependency>
Which brings in the actual Tomcat embedded jars
Spring Boot Starter Tomcat POM.xml
Because the UI application is a Spring Boot app (eg it uses the Spring Boot Parent POM and has annotated its main class with #SpringBootApplication) it will autoconfigure many things for us based on the Classpath.
Notice the #ConditionalOnClass annotation in this class:
EmbeddedServletContainerAutoConfiguration
That eventually leads to this class:
TomcatEmbeddedServletContainer
Which triggers the startup of the embedded Tomcat server.
The Default Port 8080 setting is actually coming from the embedded Tomcat dependency as seen here:
org.apache.catalina.startup.Tomcat
protected int port = 8080;

Answer 2

You can use a .properties or .yml file to store all the configuration of your application. There you can define the server port property to listen in whatever port you want.
If you use a .properties file it would be something like this :
server.port=8082
Or in a .yml file it would be something like this:
server:
port: 8082
For more about properties and configuratio in spring, check this

Answer 3

there is a reference of all spring boot default properties which should be checked as soon as you hit some unknown defaults :)
https://docs.spring.io/spring-boot/docs/current/reference/html/common-application-properties.html