/** * 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. * * @see GenericServlet * @see javax.servlet.http.HttpServlet */ publicinterfaceServlet {
/** * 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 */ publicvoidinit(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 */ publicvoidservice(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. */ publicvoiddestroy(); }
/** * Invoke the next filter in this chain, passing the specified request * and response. If there are no more filters in this chain, invoke * the <code>service()</code> method of the servlet itself. * * @param request The servlet request we are processing * @param response The servlet response we are creating * * @exception IOException if an input/output error occurs * @exception ServletException if a servlet exception occurs */ @Override publicvoiddoFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
// Call the next filter if there is one if (pos < n) { ApplicationFilterConfigfilterConfig= filters[pos++]; try { Filterfilter= filterConfig.getFilter();
// We fell off the end of the chain -- call the servlet instance try { if (ApplicationDispatcher.WRAP_SAME_OBJECT) { lastServicedRequest.set(request); lastServicedResponse.set(response); }