RestResource Annotation

The @RestResource annotation is used at the class level and enables you to expose an Apex class as a REST resource.

These are some considerations when using this annotation:

The URL mapping is relative to https://instance.salesforce.com/services/apexrest/.
A wildcard character (*) may be used.
To use this annotation, your Apex class must be defined as global.

URL Guidelines

URL path mappings are as follows:

The path must begin with a '/'
If an '*' appears, it must be preceded by '/' and followed by '/', unless the '*' is the last character, in which case it need not be followed by '/'

The rules for mapping URLs are:

An exact match always wins.
If no exact match is found, find all the patterns with wildcards that match, and then select the longest (by string length) of those.
If no wildcard match is found, an HTTP response status code 404 is returned.

The URL for a namespaced classes contains the namespace. For example, if your class is in namespace abc and the class is mapped to your_url, then the API URL is modified as follows: https://instance.salesforce.com/services/apexrest/abc/your_url/. In the case of a URL collision, the namespaced class is always used.