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* Copyright 2004 The Apache Software Foundation
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package javax.servlet;
import java.io.IOException;
/**
* Defines methods that all servlets must implement.
*
* <p>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.
*
* <p>To implement this interface, you can write a generic servlet
* that extends
* <code>javax.servlet.GenericServlet</code> or an HTTP servlet that
* extends <code>javax.servlet.http.HttpServlet</code>.
*
* <p>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:
* <ol>
* <li>The servlet is constructed, then initialized with the <code>init</code> method.
* <li>Any calls from clients to the <code>service</code> method are handled.
* <li>The servlet is taken out of service, then destroyed with the
* <code>destroy</code> method, then garbage collected and finalized.
* </ol>
*
* <p>In addition to the life-cycle methods, this interface
* provides the <code>getServletConfig</code> method, which the servlet
* can use to get any startup information, and the <code>getServletInfo</code>
* 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.
*
* <p>The servlet container calls the <code>init</code>
* method exactly once after instantiating the servlet.
* The <code>init</code> method must complete successfully
* before the servlet can receive any requests.
*
* <p>The servlet container cannot place the servlet into service
* if the <code>init</code> method
* <ol>
* <li>Throws a <code>ServletException</code>
* <li>Does not return within a time period defined by the Web server
* </ol>
*
*
* @param config a <code>ServletConfig</code> 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 <code>ServletConfig</code> object returned is the one
* passed to the <code>init</code> method.
*
* <p>Implementations of this interface are responsible for storing the
* <code>ServletConfig</code> object so that this
* method can return it. The {@link GenericServlet}
* class, which implements this interface, already does this.
*
* @return the <code>ServletConfig</code> object
* that initializes this servlet
*
* @see #init
*
*/
public ServletConfig getServletConfig();
/**
* Called by the servlet container to allow the servlet to respond to
* a request.
*
* <p>This method is only called after the servlet's <code>init()</code>
* method has completed successfully.
*
* <p> The status code of the response always should be set for a servlet
* that throws or sends an error.
*
*
* <p>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
* <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
* the Java tutorial on multi-threaded programming</a>.
*
*
* @param req the <code>ServletRequest</code> object that contains
* the client's request
*
* @param res the <code>ServletResponse</code> 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.
*
* <p>The string that this method returns should
* be plain text and not markup of any kind (such as HTML, XML,
* etc.).
*
* @return a <code>String</code> 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
* <code>service</code> method have exited or after a timeout
* period has passed. After the servlet container calls this
* method, it will not call the <code>service</code> method again
* on this servlet.
*
* <p>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();
}