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Web Applications are an integral part of any programming language. In this article, we will understand Java Web Applications in detail.
Web applications are distributed applications by nature. This means that any program that runs on more than one computer and communicates using the network and server. Web applications are accessed using a web browser so they are very popular for the ease of using the browser as a user client. The ability to update and maintain web applications without installing any software on thousands of client computers becomes a key reason for the demand.
The web application can be a simple page that shows the current date and time or a complex set of pages on which you can look up and book the most convenient flight, hotels, and car rentals for your next vacation.
The Java technologies used to create web applications are part of the Java EE platform. In order for these technologies to work on a server, the server must have a container, or web server, installed that recognizes and runs the classes you create.
There are many Java technologies to list in one article, so this article will describe the ones that are most frequently used. A web application often consists of nothing more than one page created with the JavaServer Pages (JSP) technology. Sometimes you will combine three or more such technologies. No matter how many you end up using, it is good to know what is available to you and how you can use each one in a web application.
Java Servlet API
The Java Servlet API lets you define HTTP-specific classes. A servlet class extends the capabilities of servers that host applications accessed by way of a request-response programming model. Although servlets can respond to any type of request, the most common use is to extend the applications hosted by web servers. For instance, you might use a servlet to get the text input from an online form and print it back to the screen in an HTML page and format, or you might use a different servlet to write the data to a file or database instead. A servlet runs on the server side — without an application GUI or HTML user interface (UI) of its own. Java Servlet extensions make many web applications possible.
JavaServer Pages Technology
JavaServer Pages (JSP) technology provides a simplified, fast way to create dynamic web content. JSP technology enables rapid development of web-based applications that are server- and platform-independent. JSP technology lets you add snippets of servlet code directly into a text-based document. Typically, a JSP page is a text-based document that contains two types of text:
Static data, which can be expressed in any text-based format, such as HTML, Wireless Markup Language (WML), or XML
JSP technology elements, which determine how the page constructs dynamic content
JavaServer Pages Standard Tag Library
The JavaServer Pages Standard Tag Library (JSTL) encapsulates core functionality common to many JSP technology-based applications. Instead of mixing tags from numerous vendors in your applications, you employ a single standard set of tags. This standardization allows you to deploy your applications on any JSP container that supports JSTL and makes it more likely that the implementation of the tags is optimized.
JSTL has iterator and conditional tags for handling flow control, tags for manipulating XML documents, internationalization tags, tags for accessing databases using SQL, and tags for commonly used functions.
JavaServer Faces Technology
JavaServer Faces technology is a UI framework for building web applications. The main components of JavaServer Faces technology involve a GUI component framework, a flexible model for rendering components in various markup languages and technologies, and a standard RenderKit for generating HTML markup.
Java Message Service API
Messaging is a method of communication between software components or applications. A messaging system is a peer-to-peer facility. In other words, a messaging client can send messages to and receive messages from any other client. Each client connects to a messaging agent that provides facilities for creating, sending, receiving, and reading messages. By combining Java technology with enterprise messaging, the Java Message Service (JMS) API provides a powerful tool for solving enterprise computing problems.
Enterprise messaging provides a reliable, flexible service for the exchange of business data throughout an enterprise. The JMS API adds to this a common API and provider framework that enables the development of portable message-based applications in the Java programming language. An example of how JMS might be used is an application that keeps track of inventory for an auto manufacturer.
The inventory component can send a message to the factory component when the inventory level for a product goes below a certain level, so the factory can make more cars. The factory component can send a message to the parts components so that the factory can assemble the parts it needs.The parts components in turn can send messages to their own inventory and order components to update their inventories and to order new parts from suppliers and so forth.
JavaMail API and the JavaBeans Activation Framework
Web applications can use the JavaMail API to send email notifications. The API has two parts: an application-level interface that the application components use to send an email and a service provider interface. Service providers implement particular email protocols, such as SMTP. Several service providers are included with the JavaMail API package, and others are available separately. The Java EE platform includes the JavaMail extension with a service provider that allows application components to send an email.
Java API for XML Processing
The Java API for XML Processing (JAXP), part of the Java SE platform, supports the processing of XML documents using the Document Object Model (DOM), the Simple API for XML (SAX), and Extensible Stylesheet Language Transformations (XSLT). JAXP enables applications to parse and transform XML documents independent of a particular XML-processing implementation.
JAXP also provides namespace support, which lets you work with schemas that might otherwise have naming conflicts. Designed to be flexible, JAXP lets you use any XML-compliant parser or XSL processor from within your application and supports the W3C schema.
The JDBC API allows you to invoke database SQL commands from Java programming language methods. You can use the JDBC API in a servlet, JSP technology page, or an enterprise bean when you need to access the database.
The JDBC API has two parts: an application-level interface that application components use to access a database and a service provider interface.
Java Persistence API
The Java Persistence API is a Java technology standards-based solution for persistence. Persistence uses an object-relational mapping approach to bridge the gap between an object-oriented model and a relational database. Java technology persistence consists of three areas:
The Java Persistence API
The query language
Object-relational mapping metadata
Java Naming and Directory Interface
The Java Naming and Directory Interface (JNDI) provides naming and directory functionality, enabling applications to access multiple naming and directory services. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, a web application can store and retrieve any type of named Java technology object, allowing applications to coexist with many legacy applications and systems.
Naming services provide application clients, enterprise beans, and web components with access to a JNDI naming environment. A naming environment allows the developer to customize a component without having to access or change the component’s source code. A container implements the component’s environment and provides it to the component as a JNDI naming context.
With this, we come to the end of this Java Web Application article.
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