Embedded Tomcat does not honor ServletContainerInitializers

Currently, the embedded Tomcat container does not detect and execute ServletContainerInitializers. This means that dependencies that use them are never called and therefore are unable to contribute to the running application.

The embedded Tomcat container should be enhanced such that it properly notices the ServletContainerInitializers on the Application’s classpath and executes them.

[felixbarny]

@philwebb could you be a bit more explicit what lead you to this design decision? What’s problematic about the search algorithm? Where in the boot source code do you disable that feature? Why wouldn’t you want the ServletContainerInitializer to be executed when you run java -jar? Would you consider supporting ServletContainerInitializer if some of the issues with it could be resolved?

Also it’s not magical to execute all ServletContainerInitializers. java.util.ServiceLoader.load(javax.servlet.ServletContainerInitializer) should do the trick as all implementations of that interface have to be listed in /META-INF/services/javax.servlet.ServletContainerInitializer.

Servlet 3.0 made a really good job at defining this interface and the @Web* annotations as it makes it possible to write modular extensions to web applications (like stagemonitor) that just have to be on the classpath to be active and that are completely technology agnostic. It’s really a pity that boot beaks the spec multiple times (neither ServletContainerInitializer nor @Web* annotations are supported) which makes these mechanisms useless because they don’t work with boot, which is a (btw great) technology that just can’t be ignored.

The goal of these servlet 3.0 mechanisms is to enable integration of standardized components without the user having to explicitly configure something. It’s sad that boot makes that impossible 😦

[felixbarny]

The spring-boot-samples tests are passing. Deploying the spring-boot-sample-web-jsp war to tomcat did also work. But the tests in org.springframework.boot.autoconfigure.security.oauth2.SpringSecurityOAuth2AutoConfigurationTestsare failing with the following exception:

java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[]]
    at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    at java.util.concurrent.FutureTask.get(FutureTask.java:188)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:917)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:871)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1409)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1399)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
    ... 6 more
Caused by: java.lang.IllegalStateException: No SpringApplication sources have been defined. Either override the configure method or add an @Configuration annotation
    at org.springframework.util.Assert.state(Assert.java:392)
    at org.springframework.boot.context.web.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:103)
    at org.springframework.boot.context.web.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:68)
    at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:175)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5156)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    ... 6 more

The Javadoc of SpringBootServletInitializer states:

Note that a WebApplicationInitializer is only needed if you are building a war file and
deploying it. If you prefer to run an embedded container then you won't need this at
all.

So we probably have to find a way how to not invoke SpringBootServletInitializer in case of a java -jar deployment. Do you have an idea how to do that?