Undertow is a flexible performant web server written in java, providing both blocking and non-blocking API’s based on NIO.

    Replace Tomcat in spring-boot project:

    1. <dependency>
    2.   <groupId>org.springframework.boot</groupId>
    3.   <artifactId>spring-boot-starter-web</artifactId>
    4.   <exclusions>
    5.     <exclusion>
    6.       <groupId>org.springframework.boot</groupId>
    7.       <artifactId>spring-boot-starter-tomcat</artifactId>
    8.     </exclusion>
    9.   </exclusions>
    10. </dependency>
    11. <dependency>
    12.   <groupId>org.springframework.boot</groupId>
    13.   <artifactId>spring-boot-starter-undertow</artifactId>
    14. </dependency>

    This article show that comparison of tomcat and undertow.