Spring Resource Loading

Question

Can anyone explain how Spring decides where to look for resources when one uses the ResourceLoader.getResource(...) method?

I am having a problem with a multi-module maven application built using Spring Boot whereby in my integration tests my code is able to find resources using resourceLoader.getResource("templates/") or even resourceLoader.getResource("classpath:templates/"). So far so good...

However, when the module is eventually packaged into the executable JAR and run with embedded Tomcat the resources can no longer be resolved. I also tried resourceLoader.getResource("classpath*:templates/") with no success.

What I find concerning is that when I add a logging statement to output the URL being used in the search i get a path to one of the other modules in the project (not the one that actually contains the resource in question). E.g: jar:file:/Users/david/exmaple/target/spring-boot-0.0.1-SNAPSHOT.jar!/lib/module1-0.0.1-SNAPSHOT.jar!/templates/ whereas I believe the resource is in jar:file:/Users/david/exmaple/target/spring-boot-0.0.1-SNAPSHOT.jar!/lib/module2-0.0.1-SNAPSHOT.jar!/templates/

The resource loader was obtained from an Autowired constructor param.

Thanks in advance for any hints.

Edit

Just in case it isn't clear or is of importance, my integration tests for the module in question aren't aware of the other module. I have module1, module2 and a spring-boot module which has dependencies on module1 & module2. Essentially, when I run the integration tests for module 2 the classpath isn't aware of module1 - so I suspect that this has something to do with why it works in the tests.

Answer 1

When you use classpath: or classpath*: prefix, internally, this essentially happens via a ClassLoader.getResources(…​) call in spring.

The wildcard classpath relies on the getResources() method of the underlying classloader. As most application servers nowadays supply their own classloader implementation, the behavior might differ especially when dealing with jar files. A simple test to check if classpath* works is to use the classloader to load a file from within a jar on the classpath: getClass().getClassLoader().getResources("<someFileInsideTheJar>"). Try this test with files that have the same name but are placed inside two different locations. In case an inappropriate result is returned, check the application server documentation for settings that might affect the classloader behavior.

Do not use classpath: form as you have multiple classloader locations of templates/ .

Refer to: resources-classpath-wildcards