Mapping Errors to Error Screens

When an error occurs during execution of a web application, you can have the application display a specific error screen according to the type of error. In particular, you can specify a mapping between the status code returned in an HTTP response or a Java programming language exception returned by any web component (see Handling Servlet Errors) and any type of error screen.

To set up error mappings using NetBeans IDE, do the following:

1. Open the project if you haven’t already.

2. Expand the project’s node in the Projects pane.

3. Expand the Web Pages node and then the WEB-INF node.

4. Double-click web.xml.

5. Click Pages at the top of the editor pane.

6. Expand the Error Pages node.

7. Click Add.

8. In the Add Error Page dialog:

   1. Click Browse to locate the page that you want to act as the error page.

   2. Enter the HTTP status code that will cause the error page to be opened in the Error Code field.

   3. Enter the exception that will cause the error page to load in the Exception Type field.

   4. Click OK.

Alternatively, you can click XML at the top of the editor pane and enter the error page mapping by hand using the following elements:

• An exception-type element specifying either the exception or the HTTP status code that will cause the error page to be opened.

• A location element that specifies the name of a web resource to be invoked when the status code or exception is returned. The name should have a leading forward slash (/).

• An error-page element that encloses the previous two elements.

You can have multiple error-page elements in your deployment descriptor. Each one of the elements identifies a different error that causes an error page to open. This error page can be the same for any number of error-page elements.

You can also define error screens for a JSP page contained in a WAR. If error screens are defined for both the WAR and a JSP page, the JSP page’s error page takes precedence. See Handling JSP Page Errors.

For a sample error page mapping, see the example discussed in The Example Servlets.