Rather than writing action code directly in your JSP file, you can store common functions in a tag library and implement the functions using simple tags. This practice makes the JSP file more readable and isolates the JSP file from any underlying implementation changes.
Tag libraries can be in one of the following forms:
You use the IDE to add the tag library to the web application's classpath. You use taglib directives in a JSP file to declare the tag libraries that the JSP file uses and to give each library a namespace unique within the JSP file. The tags are used in the same manner as regular XML tags with namespaces. The Source Editor provides code completion and Javadoc for tags and tag attributes of all types of tag libraries mentioned above.