Apache Struts is an open-source, Model-View-Controller (MVC) framework for building Java-based web applications. It provides a set of reusable components, such as controllers, form validation, and view components, that simplify web application development. Struts has been widely used in the development of enterprise-level web applications, and it supports various technologies like HTML, XML, JSP, and Servlet. It is considered a specialized skill because it requires a deep understanding of web application development and Java.

Enterprise JavaBeans (EJB) is a server-side component architecture for developing distributed business applications in the Java programming language. It provides a standardized way to develop and deploy reusable, scalable, and secure business components, such as session beans, entity beans, and message-driven beans. EJBs are designed to run within a Java Enterprise Edition (Java EE) container and provide services such as transaction management, security, and persistence. EJBs make it easier to build enterprise applications by allowing developers to focus on writing business logic instead of worrying about infrastructure concerns.

Java Servlet refers to a Java programming technology used to extend the capabilities of servers that host applications accessed via a request-response programming model. This skill involves creating server-side components that handle client requests, process data, and generate dynamic web content. Knowledge of Java Servlet is utilized to develop web applications by managing session data, interacting with databases, and facilitating communication between the client and server.

JavaServer Pages (JSP) is a technology used for developing server-side web applications. It allows developers to create dynamic web pages using HTML, XML, and Java code, and can be used with numerous platforms and web servers. JSP is often used in conjunction with servlets to create robust and scalable web applications. A good understanding of JSP requires knowledge of HTML, CSS, and Java programming language.

JDOM (Java Document Object Model) is a Java-based library used for working with XML documents. It provides a way to traverse, modify and create XML documents using a high-level API. It allows developers to access and manipulate data in XML files with ease, making it a popular tool for developing XML-based applications. JDOM offers a straightforward and easy-to-use model, making it easy for developers to work with complex XML files from within their Java applications.