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package javax.servlet;

import java.io.IOException;


/**
 * Defines methods that all servlets must implement.
 *
 * 

A servlet is a small Java program that runs within a Web server. * Servlets receive and respond to requests from Web clients, * usually across HTTP, the HyperText Transfer Protocol. * *

To implement this interface, you can write a generic servlet * that extends * javax.servlet.GenericServlet or an HTTP servlet that * extends javax.servlet.http.HttpServlet. * *

This interface defines methods to initialize a servlet, * to service requests, and to remove a servlet from the server. * These are known as life-cycle methods and are called in the * following sequence: *

    *
  1. The servlet is constructed, then initialized with the init method. *
  2. Any calls from clients to the service method are handled. *
  3. The servlet is taken out of service, then destroyed with the * destroy method, then garbage collected and finalized. *
* *

In addition to the life-cycle methods, this interface * provides the getServletConfig method, which the servlet * can use to get any startup information, and the getServletInfo * method, which allows the servlet to return basic information about itself, * such as author, version, and copyright. * * @author Various * * @see GenericServlet * @see javax.servlet.http.HttpServlet * */ public interface Servlet { /** * Called by the servlet container to indicate to a servlet that the * servlet is being placed into service. * *

The servlet container calls the init * method exactly once after instantiating the servlet. * The init method must complete successfully * before the servlet can receive any requests. * *

The servlet container cannot place the servlet into service * if the init method *

    *
  1. Throws a ServletException *
  2. Does not return within a time period defined by the Web server *
* * * @param config a ServletConfig object * containing the servlet's * configuration and initialization parameters * * @exception ServletException if an exception has occurred that * interferes with the servlet's normal * operation * * @see UnavailableException * @see #getServletConfig * */ public void init(ServletConfig config) throws ServletException; /** * * Returns a {@link ServletConfig} object, which contains * initialization and startup parameters for this servlet. * The ServletConfig object returned is the one * passed to the init method. * *

Implementations of this interface are responsible for storing the * ServletConfig object so that this * method can return it. The {@link GenericServlet} * class, which implements this interface, already does this. * * @return the ServletConfig object * that initializes this servlet * * @see #init * */ public ServletConfig getServletConfig(); /** * Called by the servlet container to allow the servlet to respond to * a request. * *

This method is only called after the servlet's init() * method has completed successfully. * *

The status code of the response always should be set for a servlet * that throws or sends an error. * * *

Servlets typically run inside multithreaded servlet containers * that can handle multiple requests concurrently. Developers must * be aware to synchronize access to any shared resources such as files, * network connections, and as well as the servlet's class and instance * variables. * More information on multithreaded programming in Java is available in * * the Java tutorial on multi-threaded programming. * * * @param req the ServletRequest object that contains * the client's request * * @param res the ServletResponse object that contains * the servlet's response * * @exception ServletException if an exception occurs that interferes * with the servlet's normal operation * * @exception IOException if an input or output exception occurs * */ public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException; /** * Returns information about the servlet, such * as author, version, and copyright. * *

The string that this method returns should * be plain text and not markup of any kind (such as HTML, XML, * etc.). * * @return a String containing servlet information * */ public String getServletInfo(); /** * * Called by the servlet container to indicate to a servlet that the * servlet is being taken out of service. This method is * only called once all threads within the servlet's * service method have exited or after a timeout * period has passed. After the servlet container calls this * method, it will not call the service method again * on this servlet. * *

This method gives the servlet an opportunity * to clean up any resources that are being held (for example, memory, * file handles, threads) and make sure that any persistent state is * synchronized with the servlet's current state in memory. * */ public void destroy(); }





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