Spring - Inversion of Control, Dependency Injection

Bootstrapping a web server using spring boot is simple, all we have to do is have the spring-boot-starter-web dependency in the classpath.

When the jar present in class path, and when the application it automatically configures and starts a Tomcat server that is embedded inside this jar.

Bootstrapping a web server
How to change default port number for web server

Add spring-boot-starter-web maven dependency to your project, for the below example we are using version 2.7.6. For the latest version of the jar available, check maven repository here spring-boot-starter-web

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>2.7.6</version> </dependency>

Next create a Java class with main() method and annotate the class with @SpringBootApplication.
By declaring the class with @SpringBootApplication annotation, it automatically configures the app, and applies component scan on the current package and sub package classes. This is equivalent to annotating the class with @Configuration, @EnableAutoConfiguration, and @ComponentScan.

package io.cscode.springboot.web; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class BootstrapWebServer { public static void main(String[] args) { SpringApplication.run(BootstrapWebServer.class, args); } }

Note that in the above example, we did not specify any spring profile, so it uses the default profile with default values.

When you launch the class, this automatically starts the embedded tomcat and binds to port 8080, which is the default port.

INFO 1012 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)

As you see in above example, Tomcat server started with default port number 8080, if you want to change the port number, you can suply server.port property in different ways.

You can supply server.port as JVM argument, -Dserver.port=9090
You can supply server.port as application argument, --server.port=9090

In case if you specify both, application argument --server.port value takes precedence.

You can supply it through Spring's application.properties file or application.yml file.

Below is an example specifying port number as 9090 in application.properties.

server.port=9090

Below is an example specifying port number as 9090 in application.yaml.

server: port: 9090

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