Can not find the tag library descriptor for "http://java.sun.com/jsp/jstl/core"

This error occurs when the JSTL (JavaServer Pages Standard Tag Library) core tag library is not properly included in the project.

To solve this error, you need to add the JSTL library to your project. Follow these steps:

1. Download the JSTL library from the Oracle website. Make sure to download the version that matches your servlet container or application server.

2. Extract the JSTL library to a directory of your choice.

3. Copy the JSTL JAR files to the WEB-INF/lib folder of your web application.

4. Add the following code to the beginning of your JSP file:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

This code imports the JSTL core tag library and sets the prefix to "c".

5. Save your JSP file and restart your web application.

The error should now be resolved and you should be able to use JSTL tags in your JSP file.