研究Servlet族

protected void service(HttpServletRequest req, HttpServletResponse resp)
	throws ServletException, IOException
    {
	String method = req.getMethod();

	if (method.equals(METHOD_GET)) {
	    long lastModified = getLastModified(req);
	    if (lastModified == -1) {
		// servlet doesn't support if-modified-since, no reason
		// to go through further expensive logic
		doGet(req, resp);
	    } else {
		long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
		if (ifModifiedSince < (lastModified / 1000 * 1000)) {
		    // If the servlet mod time is later, call doGet()
                    // Round down to the nearest second for a proper compare
                    // A ifModifiedSince of -1 will always be less
		    maybeSetLastModified(resp, lastModified);
		    doGet(req, resp);
		} else {
		    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
		}
	    }

	} else if (method.equals(METHOD_HEAD)) {
	    long lastModified = getLastModified(req);
	    maybeSetLastModified(resp, lastModified);
	    doHead(req, resp);

	} else if (method.equals(METHOD_POST)) {
	    doPost(req, resp);
	    
	} else if (method.equals(METHOD_PUT)) {
	    doPut(req, resp);	
	    
	} else if (method.equals(METHOD_DELETE)) {
	    doDelete(req, resp);
	    
	} else if (method.equals(METHOD_OPTIONS)) {
	    doOptions(req,resp);
	    
	} else if (method.equals(METHOD_TRACE)) {
	    doTrace(req,resp);
	    
	} else {
	    //
	    // Note that this means NO servlet supports whatever
	    // method was requested, anywhere on this server.
	    //

	    String errMsg = lStrings.getString("http.method_not_implemented");
	    Object[] errArgs = new Object[1];
	    errArgs[0] = method;
	    errMsg = MessageFormat.format(errMsg, errArgs);
	    
	    resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
	}
    }

@override
public void service(ServletRequest req, ServletResponse res)
	throws ServletException, IOException
    {
	HttpServletRequest	request;
	HttpServletResponse	response;
	
	try {
	    request = (HttpServletRequest) req;
	    response = (HttpServletResponse) res;
	} catch (ClassCastException e) {
	    throw new ServletException("non-HTTP request or response");
	}
	service(request, response);
    }

这是javax.servlet.http.HttpServlet中的两个service方法。