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: *
init method.
* service method are handled.
* 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
*
ServletException
* 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(); }