servlet3.0規範中添加了非同步處理，即一部分操作處理完成之後，先行把資料返回來，對於另一部分比較耗時的操作可以放置到另外一個執行緒中進行處理，該執行緒保留有連線的請求和響應物件，在處理完成之後可以把處理的結果通知到客戶端，例項程式碼如下：

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**   
 * @Title: AsynServlet.java 
 * @Package  
 * @Description: TODO
 * @author ynb  
 * @date 2014-7-24 下午5:07:00 
 * @version V1.0   
 */

/**
 * @author admin
 *
 */
@WebServlet(urlPatterns="/demo", asyncSupported=true)
public class AsynServlet extends HttpServlet {
	private static final long serialVersionUID = -8016328059808092454L;
	
	/* (non-Javadoc)
	 * @see javax.servlet.http.HttpServlet#service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
	 */
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		  	resp.setContentType("text/html;charset=UTF-8");
	        PrintWriter out = resp.getWriter();
	        out.println("進入Servlet的時間：" + new Date() + ".");
	        out.flush();

	        //在子執行緒中執行業務呼叫，並由其負責輸出響應，主執行緒退出
	        final AsyncContext ctx = req.startAsync();
	        ctx.setTimeout(200000);
	        new Work(ctx).start();
	        out.println("結束Servlet的時間：" + new Date() + ".");
	        out.flush();
	}
}

class Work extends Thread{
	private AsyncContext context;
	
	public Work(AsyncContext context){
		this.context = context;
	}
	@Override
	public void run() {
		try {
			Thread.sleep(2000);//讓執行緒休眠2s鐘模擬超時操作
			PrintWriter wirter = context.getResponse().getWriter();			
			wirter.write("延遲輸出");
			wirter.flush();
			context.complete();
		} catch (InterruptedException e) {
			
		} catch (IOException e) {
			
		}
	}
}
 

對於非同步執行，我們可以新增一個監聽器，監聽非同步執行的狀態。

    ctx.addListener(new AsyncListener() {
				@Override
				public void onTimeout(AsyncEvent arg0) throws IOException {
					// TODO Auto-generated method stub
					
				}
				
				@Override
				public void onStartAsync(AsyncEvent arg0) throws IOException {
					// TODO Auto-generated method stub
					
				}
				
				@Override
				public void onError(AsyncEvent arg0) throws IOException {
					// TODO Auto-generated method stub
					
				}
				
				@Override
				public void onComplete(AsyncEvent arg0) throws IOException {
					// TODO Auto-generated method stub
					
				}
			});
 

在Servlet返回之前，我們可以把持有request和response物件的AsyncContext物件放置到一個全域性可訪問的靜態容器中

map.put("id",ctx);

map.remove("id",ctx);

如下伺服器和客戶端之間資料互動的模型圖