Fix spring app name startup exception

[SylvainJuge]

What does this PR do?

Deploying https://github.com/spring-petclinic/spring-framework-petclinic application on a Tomcat server 9.0.x produces the following exception on startup:

java.lang.UnsupportedOperationException

java.lang.UnsupportedOperationException: Section 4.4 of the Servlet 3.0 specification does not permit this method to be called from a ServletContextListener that was not defined in web.xml, a web-fragment.xml file nor annotated with @WebListener at org.apache.catalina.core.StandardContext$NoPluggabilityServletContext.getClassLoader(StandardContext.java:6675) at co.elastic.apm.agent.springwebmvc.SpringServiceNameInstrumentation$SpringServiceNameAdvice.afterInitPropertySources(SpringServiceNameInstrumentation.java:75) at org.springframework.web.context.support.AbstractRefreshableWebApplicationContext.initPropertySources(AbstractRefreshableWebApplicationContext.java:214) at org.springframework.context.support.AbstractApplicationContext.prepareRefresh(AbstractApplicationContext.java:600) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:519) at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:401) at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:292) at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:103) at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4676) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5139) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:717) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:690) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:706) at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:978) at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1848) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112) at org.apache.catalina.startup.HostConfig.deployWARs(HostConfig.java:773) at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:427) at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1576) at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:309) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:123) at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:423) at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:366) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:936) at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:843) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1384) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1374) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) 

On top of that, we can already initialize the application name with getApplicationName() method on the application context.

Checklist

• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix

[felixbarny]

A minor comment. Otherwise LGTM.

[felixbarny]

Better guard against null. I've seen servletContext.getContextPath() return null on some application servers.

[SylvainJuge]

I was also wondering should we make this work for older versions of Spring framework < 3.x

[codecov-io]

Codecov Report

Merging #1464 into master will decrease coverage by 0.00%.
The diff coverage is 12.50%.

@@ Coverage Diff @@ ## master #1464 +/- ## ============================================ - Coverage 59.73% 59.72% -0.01%  Complexity 91 91 ============================================ Files 391 391 Lines 17528 17540 +12 Branches 2408 2411 +3 ============================================ + Hits 10470 10476 +6  - Misses 6340 6347 +7  + Partials 718 717 -1 

Impacted Files	Coverage Δ	Complexity Δ
...springwebmvc/SpringServiceNameInstrumentation.java	27.27% <0.00%> (-32.73%)	0.00 <0.00> (ø)
...va/co/elastic/apm/agent/impl/ElasticApmTracer.java	66.03% <100.00%> (ø)	0.00 <0.00> (ø)
...va/co/elastic/apm/agent/impl/transaction/Span.java	82.14% <100.00%> (ø)	0.00 <0.00> (ø)
...o/elastic/apm/agent/profiler/SamplingProfiler.java	72.96% <0.00%> (+0.23%)	0.00% <0.00%> (ø%)
...ic/apm/agent/profiler/collections/LongHashSet.java	17.85% <0.00%> (+1.98%)	0.00% <0.00%> (ø%)

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Build stats

• Build Cause: [Pull request #1464 updated]

• Start Time: 2020-11-03T09:57:50.233+0000

• Duration: 45 min 1 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1617
Skipped	12
Total	1629