Which method is commonly used to retrieve a resource in a RESTful web service?

In RESTful web services, the commonly used method to retrieve a resource is the GET method. This method is designed specifically for requesting data from a specified resource, allowing clients to fetch information without making any changes to the server state or the data itself.

When a client sends a GET request to a specific URI, the server processes the request and returns the requested resource, typically in a format such as JSON or XML. This function of GET aligns perfectly with the principles of REST (Representational State Transfer), which emphasizes stateless interactions and the use of standard HTTP methods.

GET requests can also be cacheable, which further enhances their efficiency when retrieving resources that do not change frequently. This makes it an ideal choice for accessing data, as it can help optimize performance by reducing load on the server and improving response times for repeated requests.

In contrast, methods like PUT, POST, and DELETE serve different purposes. PUT is primarily used to update or replace a resource, POST is used to create a new resource, and DELETE is intended for removing a resource from the server. As such, these methods do not align with the primary function of retrieving information, which is why the GET method stands out as the correct answer.