What are Java Server Pages?

JavaServer Pages (JSPs)
JavaServer Pages (JSPs) are based on the concept of server-side parsing. A JavaServer Page is an HTML page with Java statements embedded in it. The JSP specification defines certain special tags that can be embedded within the HTML page. In a normal working scenario, the JSP pages are parsed by a JSP compiler within the application server and converted into a Java servlet with the generated code embedded within the Java servlet as a set of Java statements. The generated Java servlet is then compiled as a normal servlet and loaded into the Java servlet container. The Java servlet is then used to process the user requests.

The JSP specification defines the following set of tags that can be used by application component providers:

• Directive tag— A directive tag embedded in a JSP is used to issue directives to the JSP compiler that compiles the JSP.
• Declaration tag— A declaration tag can be used by the application component provider to define variables or methods that need to be put outside the service() method of the final generated Java servlet.
• Expression tag— In order to use Java values or variables directly in the JSP, you can use the expression tag.
• Scriptlet tag— The scriptlet tag is the most important tag in the JSP specification because it enables the actual embedding of Java code within an HTML page. An application component provider can write entire processing routines within the scriptlet tags.
• Custom tag— The final set of tags that the JavaServer Page specification defines is the embedding of custom tags. Because the JSP compiler cannot process these tags on its own, a special set of classes called the JSP tag library must be built by the application component provider to support the processing of the custom tags.