It is illegal to call this method if the current request is not in asynchronous mode (i.e. isAsyncSt

源头

package jane.servlet;

import java.io.IOException;

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

@WebServlet(value = "/Async",asyncSupported = true)
public class HelloAsyncServlet extends HttpServlet
{
  /*
   * 1.首先让它支持异步处理asyncSupported = true
   * 2.开启异步模式
   */
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
  {
    System.out.println("主线程开始"+Thread.currentThread());
    AsyncContext startAsync = req.startAsync();
    startAsync.start(new Runnable()
    {
      @Override
      public void run()
      {
        try
        {
          System.out.println("子线程开始"+Thread.currentThread());
          Thread.sleep(2000);
          
          //这个说明异步处理调用完毕
          startAsync.complete();
          //然后想响应出去
          //获取到异步上下文
          AsyncContext asyncContext = req.getAsyncContext();
          //获取响应
          ServletResponse response = asyncContext.getResponse();
          response.getWriter().write("Hello World Asunc");
          System.out.println("子线程结束"+Thread.currentThread());
        } catch (Exception e)
        {
          System.out.println("异常");
          e.printStackTrace();
        }
      }
    });
    System.out.println("主线程结束"+Thread.currentThread());
  }
}

错误

java.lang.IllegalStateException: It is illegal to call this method if the current request is not in asynchronous mode (i.e. isAsyncStarted() returns false)
  at org.apache.catalina.connector.Request.getAsyncContext(Request.java:1783)
  at org.apache.catalina.connector.RequestFacade.getAsyncContext(RequestFacade.java:1068)
  at com.atguigu.servlet.HelloAsyncServlet$1.run(HelloAsyncServlet.java:32)
  at org.apache.catalina.core.AsyncContextImpl$RunnableWrapper.run(AsyncContextImpl.java:546)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
  at java.lang.Thread.run(Thread.java:745)

解决

只是startAsync.complete();这个方法调用的时机错误了,
这个方法表示异步处理完毕
应该在子线程完全处理完成业务逻辑的最后调用,就是连响应都响应完了才调用

package jane.servlet;

import java.io.IOException;

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

@WebServlet(value = "/Async",asyncSupported = true)
public class HelloAsyncServlet extends HttpServlet
{

  /*
   * 1.首先让它支持异步处理asyncSupported = true
   * 2.开启异步模式
   */
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
  {
    System.out.println("主线程开始"+Thread.currentThread());
    
    AsyncContext startAsync = req.startAsync();
    startAsync.start(new Runnable()
    {
      @Override
      public void run()
      {
        try
        {
          System.out.println("子线程开始"+Thread.currentThread());
          Thread.sleep(2000);
          
          
          //然后想响应出去
          //获取到异步上下文
          AsyncContext asyncContext = req.getAsyncContext();
          //获取响应
          ServletResponse response = asyncContext.getResponse();
          response.getWriter().write("Hello World Asunc");
          
          //这个说明异步处理调用完毕
          startAsync.complete();
          System.out.println("子线程结束"+Thread.currentThread());
        } catch (Exception e)
        {
          System.out.println("异常");
          e.printStackTrace();
        }
      }
    });
    System.out.println("主线程结束"+Thread.currentThread());
  }
}