Throw exception if spring.config.location uses classpath*:

[vkochnev]

SpringBoot version 2.3.0.M4

When trying to set spring.cloud.bootstrap.location (which is effectively mapped to spring.config.location) to something like classpath*:/config/ discovered that it doesn't work because org.springframework.boot.context.config.ConfigFileApplicationListener internally calls org.springframework.util.ResourceUtils#isUrl with supplied location and when receives false prepends it with file:. As a result it ends up with file:classpath*:/config/ in my case, which is obviously incorrect.
I filed spring-projects/spring-framework#24979 considering it might be a bug in SpringFramework, but was directed that if pattern support is desirable here then org.springframework.core.io.support.ResourcePatternUtils#isUrl should be used instead.

[philwebb]

At first I thought it would be possible to switch to ResourcePatternUtils.isUrl but I'm afraid it's not that simple. The locations specified in spring.config.location must be exact locations that can be resolved by DefaultResourceLoader. Since we don't want to support wildcards in locations, I'm going to improve the code by throwing a more specific exception.

@vkochnev Is there any reason you can't use classpath:/config/ for your location?