Spring Boot application failed to start when tomcat version is set

I'm writing here because I can't find solution to my problem. I have a Spring Boot application which is deployed on an external tomcat version 10.1.6. So to have a same tomcat version on local and prod, I set Tomcat version on build.gradle with extra["tomcat.version"] = "10.1.6". But when I do that,the application failed to start:

Spring Boot version: 3.3.4

***************************
APPLICATION FAILED TO START
***************************

Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer.customizeMaxQueueCapacity(TomcatWebServerFactoryCustomizer.java:170)

The following method did not exist:

    'void org.apache.coyote.AbstractProtocol.setMaxQueueSize(int)'

The calling method's class, org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer, was loaded from the following location:

    jar:file:/Users/USER/.gradle/caches/modules-2/files-2.1/org.springframework.boot/spring-boot-autoconfigure/3.3.4/979234a0f3035fe60d5e505018789f98a7ec7ee3/spring-boot-autoconfigure-3.3.4.jar!/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.class

The called method's class, org.apache.coyote.AbstractProtocol, is available from the following locations:

    jar:file:/Users/USER/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-core/10.1.6/abacfdcc788fafbf671c6f68338bd2d5c27411e7/tomcat-embed-core-10.1.6.jar!/org/apache/coyote/AbstractProtocol.class

The called method's class hierarchy was loaded from the following locations:

    org.apache.coyote.AbstractProtocol: file:/Users/USER/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-core/10.1.6/abacfdcc788fafbf671c6f68338bd2d5c27411e7/tomcat-embed-core-10.1.6.jar


Action:

Correct the classpath of your application so that it contains compatible versions of the classes org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer and org.apache.coyote.AbstractProtocol


Process finished with exit code 1

To explain my problem, I have created a sample project with Spring Initializr: https://github.com/amourier63/spring-boot-set-tomcat-version

In the Build.gradle.kts line 23. If I comment the line and launch the project, the project start. But when I uncomment, the start failed.

I take any suggestion... and maybe set the tomcat version is a bad idea.

Thank you

Solution

The AbstractProtocol.setMaxQueueSize() method was introduced in Apache Tomcat v10.1.25 (source) and it's set as soon as server.tomcat.threads.max-queue-capacity is configured (and that property has a default value).

So in short, Spring Boot v3.3.4 is not compatible with Apache Tomcat v10.1.6.

Possible solutions are:

Updating your external Tomcat to v10.1.25 or higher (I would recommend to go to the latest v10.1.x or v10.1.30 as that's the version Spring Boot v3.3.4 uses as default).
Alternatively, you could set the server.tomcat.threads.max-queue-capacity to a non-positive value, because in that case TomcatWebServerFactoryCustomizer does not invoke the setMaxQueueSize() method (source). I don't recommend this though.
```
server.tomcat.threads.max-queue-capacity=0
```
Downgrade Spring Boot to v3.3.0. This feature was introduced in Spring Boot v3.3.1 (see issue), so downgrading to v3.3.0 would not cause this error to happen. I don't recommend this either.
Since the error only happens in the embedded Tomcat configuration (which I assume you use for development?), you could also remove the <tomcat.version> property and run locally on the latest supported Tomcat 10.1.x version, while you deploy your WAR-file on Tomcat 10.1.6.