How can I change server in spring boot application?

The default Embedded Web Servers in Spring-Boot is Tomcat, but you can easily change it to others.

First of all, you need to exclude tomcat:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <!-- Exclude the Tomcat dependency -->
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Then you can add your desired embedded web server:

<!-- Jetty Embedded Web Server -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency> 

or

<!-- Undertow Embedded Web Server -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency> 

# Gradle way

     implementation 'org.springframework.boot:spring-boot-starter-tomcat'
     implementation 'org.springframework.boot:spring-boot-starter-jetty'
     modules {
      module("org.springframework.boot:spring-boot-starter-tomcat") {
          replacedBy("org.springframework.boot:spring-boot-starter-jetty", "Use Jetty instead of Tomcat")
      }
     }

# Gradle Another Way

    compile('org.springframework.boot:spring-boot-starter-webflux') {
        exclude group: 'org.springframework.boot',
        module: 'spring-boot-starter-reactor-netty'
    }
    compile('org.springframework.boot:spring-boot-starter-tomcat')

You will need to update pom.xml, add the dependency for spring-boot-starter-jetty. Also, you will need to exclude default added spring-boot-starter-tomcat dependency.

<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-jetty</artifactId>
</dependency>

In gradle,

configurations {
    compile.exclude module: "spring-boot-starter-tomcat"
}
 
dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    compile("org.springframework.boot:spring-boot-starter-jetty")
}

You have to exclude tomcat from starter dependency:

<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>

and now you need to include new server as a dependency i.e.:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>