主要增加了以下特性：
1、异步处理支持
2、可插性支持
3、注解支持，零配置，可不用配置web.xml
...
异步处理是什么鬼？
直接操起键盘干。
@WebServlet(name = "index", urlPatterns = { "/" }, asyncSupported = true)
public class IndexServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.setContentType("text/html"); try { PrintWriter out = resp.getWriter(); out.println("servlet started.<br/>"); out.flush(); AsyncContext asyncContext = req.startAsync(); asyncContext.addListener(getListener()); asyncContext.start(new IndexThread(asyncContext)); out.println("servlet end.<br/>"); out.flush(); } catch (Exception e) { e.printStackTrace(); } } /** * 异步线程结果监听 * @author javastack * @return */ private AsyncListener getListener() { return new AsyncListener() { public void onComplete(AsyncEvent asyncEvent) throws IOException { asyncEvent.getSuppliedResponse().getWriter().close(); System.out.println("thread completed."); } public void onError(AsyncEvent asyncEvent) throws IOException { System.out.println("thread error."); } public void onStartAsync(AsyncEvent asyncEvent) throws IOException { System.out.println("thread started."); } public void onTimeout(AsyncEvent asyncEvent) throws IOException { System.out.println("thread timeout."); } }; } } public class IndexThread implements Runnable { private AsyncContext asyncContext; public IndexThread(AsyncContext asyncContext) { this.asyncContext = asyncContext; } public void run() { try { Thread.sleep(5000); PrintWriter out = asyncContext.getResponse().getWriter(); out.println("hello servlet3.<br/>"); out.flush(); asyncContext.complete(); } catch (Exception e) { e.printStackTrace(); } } }
访问localhost:8080/test
页面首先输出
servlet started. servlet end.
过了5秒后再输出
hello servlet3.
可以看出servlet立马返回了，但没有关闭响应流，只是把response响应传给了线程，线程再继续输出，我们可以将比较费资源消耗时间的程序放到异步去做，这样很大程序上节省了servlet资源。
Springmvc3.2开始也加入了servlet3异步处理这个特性，有兴趣的同学可以去研究下。
从上面的servlet注解也可以看出来，servlet3完全解放了web.xml配置，通过注解可以完全代替web.xml配置。
