Allow the TTL of Tomcat's resource cache to be configured via the environment

[bohrqiu]

All http request served by tomcat will validateResource,when StandardRoot has too many resouces(org.apache.catalina.webresources.StandardRoot#allResources),the performance is slow. spring-boot 1.5.1 has the problem，allResources contains all classpath library. thanks committers ,this have been fixed at spring-boot 1.5.4.

but when app run in fatjar or war，resource can't be change anymore,tomcat org.apache.catalina.webresources.Cache#ttl is too short(default is 5 second).

in my case ,i had set the cache as follows:

 ((TomcatEmbeddedServletContainerFactory)factory).addContextLifecycleListeners(
          event -> {
            if (event.getType().equals(Lifecycle.CONFIGURE_START_EVENT)) {
              ((StandardContext) event.getLifecycle())
                  .getResources()
                  .setCacheTtl(100l * 24 * 60 * 60 * 1000);//set cache ttl 100 days
            }
          });

can there be have some default strategy for this?

[philwebb]

I'm not sure that we can safely make the assumption that because someone is running a fat war, the Tomcat resources won't change. The WebResourceRoot interface is quite general and can cover resources from a variety of different sources. I'm also not keen to deviate from the Tomcat defaults.

Are you seeing any practical problems with the default timeout? Are there performance issues?

My initial feeling is that we shouldn't change the defaults, but perhaps we could make things easier to configure.

[bohrqiu]

Yes, we've had performance issues at spring-boot 1.5.1 because of spring-boot add all classpath jar to tomcat resouces(org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory.StoreMergedWebXmlListener#onStart L826).

TomcatResources.get(context).addClasspathResources();

and at spring-boot 1.5.4, TomcatEmbeddedServletContainerFactory L228
TomcatResources.get(context).addResourceJars(TomcatEmbeddedServletContainerFactory.this.getUrlsOfJarsWithMetaInfResources());

When cache is expired,all jar will be check if contain the resource. If there have easy configure property will be better.