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();
}