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The Hypertext Transfer Protocol (HTTP) is an application-level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods (commands). A feature of HTTP is the typing of data representation, allowing systems to be built independently of the data being transferred. The HTTP is based on a request/response paradigm. A client establishes a connection with a server and sends a request to the server in the form of a request method, URL, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible body content. The server responds with a status line, including the message's protocol version and a success or error code, followed by a MIME-like message containing serv...

Singleton [GOF] One instance of a class or one value accessible globally in an application Where to use & benefits Ensure unique instance by defining class final to prevent cloning. May be extensible by the subclass by defining subclass final. Make a method or a variable public or/and static. Access to the instance by the way you provided. Well control the instantiation of a class. Define one value shared by all instances by making it static. One file system, one window manager, one printer spooler, one Test engine, one Input/Output socket and etc. To design a Singleton class, you may need to make the class final like java.Math, which is not allowed to subclass, or make a variable or method public and/or static, or make all constructors private to prevent the compiler from creating a default one. For example, to make a unique remote connection, final class RemoteConnection { private Connect con; private static RemoteConnection rc = new RemoteConnection(connection)...

What Is a Servlet? A servlet is a Java programming language class used to extend the capabilities of servers that host applications accessed via a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by Web servers. For such applications, Java Servlet technology defines HTTP-specific servlet classes. The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing servlets. All servlets must implement the Servlet interface, which defines life-cycle methods. When implementing a generic service, you can use or exte nd the GenericServlet class provided with the Java Servlet API. The HttpServlet class prov ides methods, such as doGet and doPost , for handling HTTP-specific services. Servlet Life Cycle The life cycle of a servlet is controlled by the container in which the servlet has been deployed. When a request is mapped to a ser...