Servlets Interview Questions And Answers - DoAnswers.com

Servlets are the Java platform technology of choice for extending and enhancing Web servers. Servlets provide a component-based, platform-independent method for building Web-based applications, without the performance limitations of CGI programs. And unlike proprietary server extension mechanisms (such as the Netscape Server API or Apache modules), servlets are server- and platform-independent. This leaves you free to select a "best of breed" strategy for your servers, platforms, and tools.

Servlets have access to the entire family of Java APIs, including the JDBC API to access enterprise databases. Servlets can also access a library of HTTP-specific calls and receive all the benefits of the mature Java language, including portability, performance, reusability, and crash protection.

Today servlets are a popular choice for building interactive Web applications. Third-party servlet containers are available for Apache Web Server, Microsoft IIS, and others. Servlet containers are usually a component of Web and application servers, such as BEA WebLogic Application Server, IBM WebSphere, Sun Java System Web Server, Sun Java System Application Server, and others.

You might want to check out the latest information on JavaServer Pages (JSP) technology. JSP technology is an extension of the servlet technology created to support authoring of HTML and XML pages. It makes it easier to combine fixed or static template data with dynamic content. Even if you're comfortable writing servlets, there are several compelling reasons to investigate JSP technology as a complement to your existing work.

Sessions tracking using Cookies are more secure and fast. Session tracking using Cookies can also be used with other mechanism of Session Tracking like url rewriting. Cookies are stored at client side so some clients may disable cookies so we may not sure that the cookies may work or not. In url rewriting requites large data transfer from and to the server. So, it leads to network traffic and access may be become slow.

Question: What are methods of HttpServlet? Java Servlets have a number of advantages over CGI and other API's. They are: Platform Independence Java Servlets are 100% pure Java, so it is platform independence. It can run on any Servlet enabled web server. For example if you develop an web application in windows machine running Java web server. You can easily run the same on apache web server (if Apache Serve is installed) without modification or compilation of code. Platform independency of servlets provide a great advantages over alternatives of servlets. Performance Due to interpreted nature of java, programs written in java are slow. But the java servlets runs very fast. These are due to the way servlets run on web server. For any program initialization takes significant amount of time. But in case of servlets initialization takes place very first time it receives a request and remains in memory till times out or server shut downs. After servlet is loaded, to handle a new request it simply creates a new thread and runs service method of servlet. In comparison to traditional CGI scripts which creates a new process to serve the request. This intuitive method of servlets could be use to develop high speed data driven web sites. Extensibility Java Servlets are developed in java which is robust, well-designed and object oriented language which can be extended or polymorphed into new objects. So the java servlets takes all these advantages and can be extended from existing class the provide the ideal solutions. Safety Java provides a very good safety features like memory management, exception handling etc. Servlets inherits all these features and emerged as a very powerful web server extension. Secure Servlets are server side components, so it inherits the security provided by the web server. Servlets are also benefited with Java Security Manager.

Core classes of Struts Framework are ActionForm, Action, ActionMapping, ActionForward, ActionServlet etc.

HttpServlet Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these: doGet, if the servlet supports HTTP GET requests doPost, for HTTP POST requests doPut, for HTTP PUT requests doDelete, for HTTP DELETE requests init and destroy, to manage resources that are held for the life of the servlet getServletInfo, which the servlet uses to provide information about itself There's almost no reason to override the service method. service handles standard HTTP requests by dispatching them to the handler methods for each HTTP request type (the doXXX methods listed above). Likewise, there's almost no reason to override the doOptions and doTrace methods. GenericServlet defines a generic, protocol-independent servlet. To write an HTTP servlet for use on the Web, extend HttpServlet instead. GenericServlet implements the Servlet and ServletConfig interfaces. GenericServlet may be directly extended by a servlet, although it's more common to extend a protocol-specific subclass such as HttpServlet. GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface. GenericServlet also implements the log method, declared in the ServletContext interface. To write a generic servlet, you need only override the abstract service method.

Servlets are server side components that runs on the Servlet container. Applets are client side components and runs on the web browsers. Servlets have no GUI interface.

Web component follows the standard directory structure defined in the J2EE specification. Directory Structure of Web Component / index.htm, JSP, Images etc.. Web-inf web.xml classes servlet classes lib jar files

The interface javax.servlet.Servlet, defines the three life-cycle methods. These are: public void init(ServletConfig config) throws ServletException public void service( ServletRequest req, ServletResponse res) throws ServletException, IOException public void destroy() The container manages the lifecycle of the Servlet. When a new request come to a Servlet, the container performs the following steps. 1. If an instance of the servlet does not exist, the web container * Loads the servlet class. * Creates an instance of the servlet class. * Initializes the servlet instance by calling the init method. Initialization is covered in Initializing a Servlet. 2. The container invokes the service method, passing request and response objects. 3. To remove the servlet, container finalizes the servlet by calling the servlet's destroy method.

38. What are the objects that are received when a servlets accepts call from client?

The objects are ServeltRequest and ServletResponse . The ServeltRequest encapsulates the communication from the client to the server. While ServletResponse encapsulates the communication from the Servlet back to the client.

It extends the GenericServlet base class and provides an framework for handling the HTTP protocol. So, HttpServlet only supports HTTP and HTTPS protocol.

There are two types of servlets, GenericServlet and HttpServlet. GenericServlet defines the generic or protocol independent servlet. HttpServlet is subclass of GenericServlet and provides some http specific functionality linke doGet and doPost methods.