How does the embedded server work in Spring Boot (Tomcat, Jetty, Undertow)? स्प्रिंग बूट में एम्बेडेड सर्वर (Tomcat, Jetty, Undertow) कैसे काम करता है?

Spring Boot embeds a servlet container directly inside the executable JAR instead of requiring deployment to an external application server.

spring-boot-starter-web pulls in Tomcat by default; the container is auto-configured and started when SpringApplication.run() executes, bound to the port defined by server.port. Because the server is part of the JAR, the app runs with a single java -jar command, simplifying containerization. Switching to Jetty or Undertow only requires excluding the Tomcat starter and adding the alternative starter.

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <exclusions>
    <exclusion>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>