Java-Servlet

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
     * <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
     */
	//servlet一旦被实例化servlet容器开始调用init函数
    public void init(ServletConfig config) throws ServletException;
    //返回一个ServletConfig对象，包含了此Servlet的初始化和启动参数
    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
     *
     */
    //servlet容器调用允许回复一个请求，Servlet通常运行在一个多线程的Servlet容器中，可以同时处理多个请求，开发者要注意某些资源（文件、类、实例）的同步问题。
    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
     *
     */
    //返回servlet的信息，比如作者，版本，版权
    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.
     *
     */
    //被servlet container调用，从服务中去掉
    public void destroy();
}