2.4. The ResourceLoader

The ResourceLoader interface is meant to be implemented by objects that can return (that is, load) Resource instances. The following listing shows the ResourceLoader interface definition:

public interface ResourceLoader {

    Resource getResource(String location);
}

All application contexts implement the ResourceLoader interface. Therefore, all application contexts may be used to obtain Resource instances.

When you call getResource() on a specific application context, and the location path specified doesn’t have a specific prefix, you get back a Resource type that is appropriate to that particular application context. For example, assume the following snippet of code was executed against a ClassPathXmlApplicationContext instance:

Resource template = ctx.getResource("some/resource/path/myTemplate.txt");

Against a ClassPathXmlApplicationContext, that code returns a ClassPathResource. If the same method were executed against a FileSystemXmlApplicationContext instance, it would return a FileSystemResource. For a WebApplicationContext, it would return a ServletContextResource. It would similarly return appropriate objects for each context.

As a result, you can load resources in a fashion appropriate to the particular application context.

On the other hand, you may also force ClassPathResource to be used, regardless of the application context type, by specifying the special classpath: prefix, as the following example shows:

Resource template = ctx.getResource("classpath:some/resource/path/myTemplate.txt");

Similarly, you can force a UrlResource to be used by specifying any of the standard java.net.URLprefixes. The following pair of examples use the file and http prefixes:

Resource template = ctx.getResource("file:///some/resource/path/myTemplate.txt");

Resource template = ctx.getResource("https://myhost.com/resource/path/myTemplate.txt");

The following table summarizes the strategy for converting String objects to Resource objects: