It’s intended to store service provider configuration files.
A Service provider is an implementation of a Service Provider Interface packaged as JAR.
A Service loader discover and load all implementations declared in the service provider configuration file.
A configuration file is a file named as the fully qualified name of the interface and its content is a list of fully qualified names of implementations.
Following is an example of provider configuration file for javax.servlet.ServletContainerInitializer that is used by Servlet 3.0 at webapp startup.
org.apache.jasper.servlet.JasperInitializer
org.springframework.web.SpringServletContainerInitializer
In this example
- Tomcat is the Service Loader;
- javax.servlet.ServletContainerInitializer is the Service Provider Interface
- file named javax.servlet.ServletContainerInitializer is the Service Provider configuration file;
- org.apache.jasper.servlet.JasperInitializer and org.springframework.web.SpringServletContainerInitializer are Service providers
When tomcat startup webapp call both
onStartup(java.util.Set<java.lang.Class<?>> types, ServletContext context)
methods on JasperInitializer and SpringServletContainerInitializer classes