Whizu

How to programmatically throw a 404 error from a servlet

Written by Rudy D'hauwe on June 10, 2013.

This article explains how to throw and send a 404 status code from within a Java servlet. A 404 status code is most commonly set on the HTTP response when a page or resource is requested that cannot be found.

Http Status Codes

When a web server responds to a request from a browser or other web client, the response typically consists of a status line, some response headers, a blank line, and the document.

Here is a minimal example:

HTTP/1.1 200 OK 
Content-Type: text/plain

Hello World

The status line consists of the HTTP version, an integer that is interpreted as a status code, and a very short message corresponding to the status code. In most cases, all of the headers are optional except for Content-Type, which specifies the MIME type of the document that follows.

Servlets can perform a variety of tasks by manipulating the status line and the response headers. For example, they can forward the user to other sites; indicate that the attached document is an image, an Adobe Acrobat file, or most commonly an HTML file; tell the user that a password is required to access the document; and so forth.

This article explains how to set the status code from within a Java servlet indicating that a page or resource cannot be found.

It's easy :-)

The Servlet API gives you a method to send a 404 or any other HTTP status code. It's done with the sendError method of HttpServletResponse.

public void doGet(HttpServletRequest req, HttpServletResponse res) {
    res.sendError(HttpServletResponse.SC_NOT_FOUND);
}