Servlets

                       Basic Information about Servlets in Java:

1. Servlets are server side components that provide a powerful mechanism for developing server side programs. Servlets provide component-based, platform-independent methods for building Web-based applications, without the performance limitations of CGI programs.

2.Unlike proprietary server extension mechanisms (such as the Netscape Server API or Apache modules), servlets are server as well as platform-independent. This leaves you free to select a "best of breed" strategy for your servers, platforms, and tools. Using servlets web developers can create fast and efficient server side application which can run on any servlet enabled web server.

3.Servlets run entirely inside the Java Virtual Machine. Since the Servlet runs at server side so it does not checks the browser for compatibility. Servlets can access the entire family of Java APIs, including the JDBC API to access enterprise databases. 

4.Servlets can also access a library of HTTP-specific calls, receive all the benefits of the mature java language including portability, performance, reusability, and crash protection. Today servlets are the popular choice for building interactive web applications. 

5.Third-party servlet containers are available for Apache Web Server, Microsoft IIS, and others. Servlet containers are usually the components 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.

6.Servlets are not designed for a specific protocols. It is different thing that they are most commonly used with the HTTP protocols Servlets uses the classes in the java packages javax.servlet and javax.servlet.http. Servlets provides a way of creating the sophisticated server side extensions in a server as they follow the standard framework and use the highly portable java language.

                                                   Uses of Servlets:

a)Priovide dynamic content like getting the results of a database query and returning to the client.

b)Process and/or store the data submitted by the HTML.

c)Manage information about the state of a stateless HTTP. e.g. an online shopping car manages request for multiple concurrent customers.

                   Certain Servlets interview Q/As

Q1. What is a servlet ?

Servlets are modules that extend request/response-oriented servers,such as Java-enabled web servers. For example, a servlet might be responsible for taking data in an HTML order-entry form and applying the business logic used to update a company’s order database. Servlets are to servers what applets are to browsers. Unlike applets, however, servlets have no graphical user interface.

Q2. Whats the advantages using servlets over using CGI?
Servlets provide a way to generate dynamic documents that is both easier to write and faster to run. Servlets also address the problem of doing server-side programming with platform-specific APIs: they are developed with the Java Servlet API, a standard Java extension.

Q3. What are the general advantages and selling points of Servlets?
A servlet can handle multiple requests concurrently, and synchronize requests. This allows servlets to support systems such as online real-time conferencing. Servlets can forward requests to other servers and servlets. Thus servlets can be used to balance load among several servers that mirror the same content, and to partition a single logical service over several servers, according to task type or organizational boundaries.

Q4. Which package provides interfaces and classes for writing servlets? 
javax

Q5. What’s the Servlet Interface?
The central abstraction in the Servlet API is the Servlet interface. All servlets implement this interface, either directly or, more commonly, by extending a class that implements it such as HttpServlet.Servlets > Generic Servlet > HttpServlet > MyServlet. The Servlet interface declares, but does not implement, methods that manage the servlet and its communications with clients. Servlet writers provide some or all of these methods when developing a servlet.

Q6. When a servlet accepts a call from a client, it receives two objects. What are they?
ServletRequest (which encapsulates the communication from the client to the server) and ServletResponse (which encapsulates the communication from the servlet back to the client). ServletRequest and ServletResponse are interfaces defined inside javax.servlet package.

Q7. What information does ServletRequest allow access to?
Information such as the names of the parameters passed in by the client, the protocol (scheme) being used by the client, and the names of the remote host that made the request and the server that received it. Also the input stream, as ServletInputStream.Servlets use the input stream to get data from clients that use application protocols such as the HTTP POST and GET methods.

Q8. What type of constraints can ServletResponse interface set on the client?
It can set the content length and MIME type of the reply. It also provides an output stream, ServletOutputStream and a Writer through which the servlet can send the reply data.

Q9. Explain servlet lifecycle?
Each servlet has the same life cycle: first, the server loads and initializes the servlet (init()), then the servlet handles zero or more client requests (service()), after that the server removes the servlet (destroy()). Worth noting that the last step on some servers is done when they shut down.

Q10. How does HTTP Servlet handle client requests?
An HTTP Servlet handles client requests through its service method. The service method supports standard HTTP client requests by dispatching each request to a method designed to handle that request.