According to the spring.io docs, stand-alone Spring Boot applications can be packaged as a WAR or JAR, which can be deployed to any Servlet 3.1+ compatible container.

You might think this is possible out of the box, but in reality we’ll need a couple of tweaks. Nothing too complicated.

Let’s use the example REST service application provided by the Spring guides.  As a quick reminder, all this app does is respond to HTTP Get requests with a greeting in JSON format.

To deploy the app to an external server, first we extend SpringBootServletInitializer; this is the only change in the application code we are going to need.

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Next we edit the gradle.build file.

Remember that Spring Boot apps run in the embedded Tomcat Server. Since our target HTTP runtime (WildFly) uses the Undertow servlet, we don’t want any Tomcat stuff on the classpath.

Let’s exclude the spring-boot-starter-tomcat module from the parent project.

gradle.build

configurations {
    all.collect { configuration ->
        configuration.exclude   group: 'org.springframework.boot', module: 'spring-boot-starter-tomcat'
    }
}

Next we declare a dependency to javax.servlet module.

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    compile("javax.servlet:javax.servlet-api:3.1.0")
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

Finally let’s add the WAR plugin.

plugins {
    id 'war'
}

Now try to package the app using ./gradlew bootWar. If this succeeds, you should be able to deploy the file to WildFly without errors.

Note that WildFly will use the application name as the context root. Visit http://localhost:8080/gs-rest-service/greeting to test the result.

{"id":1,"content":"Hello, World!"}

Hope it helps.