servlet3.0 异步servlet

假设一种情况，你的一个servlet会处理比较长的时间，而且这个servlet请求数量也挺多的，那么久会造成tomcat线程池被占用满了，造成其他用户的请求等待队列过多，时间过长。

用例子实现
首先需要开启

<servlet>
    <servlet-name>webProxyMain</servlet-name>
    <servlet-class>com.lsiding.nat.server.web.WebProxyMain</servlet-class>
    <load-on-startup>1</load-on-startup>
    <async-supported>true</async-supported>
  </servlet>

或者

@WebServlet(value = "/asyncTest", asyncSupported=true)

package com.lsiding.admin4j.act;

import java.io.IOException;

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

/**
 * Servlet implementation class AsyncTest
 */
@WebServlet(value = "/asyncTest.html", asyncSupported = true)
public class AsyncTest extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public AsyncTest() {
		super();
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setCharacterEncoding("utf-8");
		// 必须
		// 否则可能会 A filter or servlet of the current chain does not support
		// asynchronous operations.
		request.setAttribute("org.apache.catalina.ASYNC_SUPPORTED", true);
		AsyncContext asyncCtx = request.startAsync();
		asyncCtx.addListener(new AppAsyncListener());
		asyncCtx.setTimeout(9000);
		asyncCtx.start(
		new Thread() {
			public void run() {
				try {
					try {
						asyncCtx.getResponse().getOutputStream()
								.println("thread");
						asyncCtx.getResponse().getOutputStream().flush();
					} catch (IOException e) {
					}
					Thread.sleep(8000);
					asyncCtx.complete();
				} catch (InterruptedException e) {
				}
				;
			}
		});
		response.getOutputStream()
				.write("请求方法返回了，但是response是否结束了呢？".getBytes());
		response.getOutputStream().flush();
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}
}

package com.lsiding.admin4j.act;

import java.io.IOException;

import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;

public class AppAsyncListener implements AsyncListener {
	@Override
	public void onComplete(AsyncEvent asyncEvent) throws IOException {
		asyncEvent.getAsyncContext().getResponse().getOutputStream().println("onComplete");
		asyncEvent.getAsyncContext().getResponse().getOutputStream().flush();
	}

	@Override
	public void onError(AsyncEvent asyncEvent) throws IOException {
		asyncEvent.getAsyncContext().getResponse().getOutputStream().println("onError");
		asyncEvent.getAsyncContext().getResponse().getOutputStream().flush();
	}

	@Override
	public void onStartAsync(AsyncEvent asyncEvent) throws IOException {
		asyncEvent.getAsyncContext().getResponse().getOutputStream().println("onStartAsync");
		asyncEvent.getAsyncContext().getResponse().getOutputStream().flush();
	}

	@Override
	public void onTimeout(AsyncEvent asyncEvent) throws IOException {
		asyncEvent.getAsyncContext().getResponse().getOutputStream().println("asyncEvent");
		asyncEvent.getAsyncContext().getResponse().getOutputStream().flush();
	}
}