The ServletRequest interface in Java provides a way for servlets to receive and process HTTP requests. It is implemented by the web container and is passed to the servlet's service method when a client sends a request to the servlet. The ServletRequest object contains all the information about the request, including the HTTP headers, cookies, and parameters.

The ServletRequest interface defines a number of methods that can be used by the servlet to access information about the request. Some of the most commonly used methods include:

• getParameter(name): Returns the value of the named parameter sent with the request, or null if the parameter was not sent.
• getParameterNames(): Returns an Enumeration of all the parameter names sent with the request.
• getInputStream(): Returns an input stream for reading the request body.
• getHeader(name): Returns the value of the named HTTP header sent with the request, or null if the header was not sent.
• getHeaderNames(): Returns an Enumeration of all the HTTP header names sent with the request.

The ServletRequest interface also provides methods for retrieving information about the client, such as the IP address, host name, and user agent. In addition, it provides methods for retrieving the servlet context, the servlet path, and the path info for the request.

Overall, the ServletRequest interface is an essential part of the Java Servlet API, as it provides the mechanism for servlets to process incoming requests and generate responses.