Add a Tomcat 11 smoke test

[sephiroth-j]

Tomcat 11.0.0 was released last week and it would be nice if Spring Boot 3.4 would support the new version. This requires at least changing TomcatWebServerFactoryCustomizer.customizeRejectIllegalHeader as it uses a previously deprecated method setRejectIllegalHeader which was removed with Tomcat 11.0.

spring-boot/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java

Line 227 in 35a3ff9

protocol.setRejectIllegalHeader(rejectIllegalHeader);

Catching a NoSuchMethodError would be sufficient and is something that is already done in customizeRemoteIpValve.

spring-boot/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java

Lines 251 to 257 in 35a3ff9

	try {
	valve.setHostHeader(remoteIpProperties.getHostHeader());
	}
	catch (NoSuchMethodError ex) {
	// Avoid failure with war deployments to Tomcat 8.5 before 8.5.44 and
	// Tomcat 9 before 9.0.23
	}

[wilkinsona]

With 3.4.0-RC1 only a week away, I'm afraid it's too late for us to support Tomcat 11 in Boot 3.4. Furthermore, Tomcat 11 is a Servlet 6.1 (Jakarta EE 11) compatibile container and exceeds our baseline. We may consider supporting Tomcat 11 in Spring Boot 3.5 alongside Tomcat 10 (which would likely remain the default) but it may also have to wait for Spring Boot 4.0 in a year's time.

In the meantime, this issue has led to me noticing that we should have removed support for configuring rejectIllegalHeader as it has been deprecated for some time now. I've opened #42731 to do that. This may get things working with Tomcat 11 but please note that if it works it still wouldn't be supported and you would be using Tomcat 11 at your own risk with no guarantee that we'll make further changes in 3.4.x to address any other problems that you may encounter.

[sephiroth-j]

I've opened #42731 to do that.

Thanks, that should be enough for now. Then we can test whether the new version works without being officially supported.

[philwebb]

I've added a smoke test for Tomcat 11 that should give us some confidence that at least the basics work. As Andy said above, there's no guarantee that we'll be able to make further changes in 3.4.x to address any other problems that may arise.

[wilkinsona]

I'm not sure that this should be an enhancement as I think it may set expectations too high. I think a task would be better.