servlet3.0 之同步与异步

servlet3.0之前：SyncServlet:同步阻塞

servlet3.0之后：支持AsyncServlet:异步非阻塞

下面代码体会下如何开启异步处理：

import java.io.IOException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.TimeUnit;

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

/**
 * Servlet implementation class AsyncServlet
 */
@WebServlet(asyncSupported = true, urlPatterns = { "/AsyncServlet" })
public class AsyncServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public AsyncServlet() {
		super();
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		long t1 = System.currentTimeMillis();

		// 开启异步
		AsyncContext asyncContext = request.startAsync();

		// 执行业务代码
		CompletableFuture.runAsync(() -> doSomeThing(asyncContext,
				asyncContext.getRequest(), asyncContext.getResponse()));

		System.out.println("async use:" + (System.currentTimeMillis() - t1));
	}

	private void doSomeThing(AsyncContext asyncContext,
			ServletRequest servletRequest, ServletResponse servletResponse) {

		// 模拟耗时操作
		try {
			TimeUnit.SECONDS.sleep(5);
		} catch (InterruptedException e) {
		}

		//
		try {
			servletResponse.getWriter().append("done");
		} catch (IOException e) {
			e.printStackTrace();
		}

		// 业务代码处理完毕, 通知结束
		asyncContext.complete();
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

总结流程：

1.开启异步上下文

2.将业务代码放到独立的线程池执行

3.执行完毕之后关闭异步上下文