Question

我正在尝试编写一个线程化的Java EE servlet 每个线程都会进行一些处理并将其结果写入一个HTTP块（使用HTTP Transfer-encoding：chunked）每个块一旦可用就会立即发送给客户端我在每个帖子中编写和刷新输出时遇到问题为了举例，下面的代码产生5个生成随机字符串的线程，将其写入输出缓冲区并通过同步函数调用刷新该缓冲区。

public class TestServer extends HttpServlet {
   private PrintWriter m_out;

   public TestServer() {
      super();
   }

   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      m_out = response.getWriter();

      m_out.print("gonna start\n");
      m_out.flush();

      ThreadPoolExecutor thread_pool = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
      for(int i = 0; i < 5; i++ ) {
         thread_pool.execute(new Runnable() {
        private ReentrantLock m_lock = new ReentrantLock();
        @Override
        public void run() {
               SecureRandom random = new SecureRandom();
               m_lock.lock();
               try {
                  display(new BigInteger(1300, random).toString(32)+"\n");
               }
               finally {
                  m_lock.unlock();
               }
            }
         });
      }
      thread_pool.shutdown();
      try {
         thread_pool.awaitTermination(120, TimeUnit.SECONDS);
      }
      catch (InterruptedException e1) {
         log("thread interrupted");
         e1.printStackTrace();
      }
      m_out.print("ok we done\n");
      m_out.close();
   }

   void display(String content) {
      m_out.print(content);
      m_out.flush();
   }
}

偶尔，此代码将生成以下输出：

Server: Apache-Coyote/1.1
Transfer-Encoding: chunked
Date: Mon, 14 Mar 2011 22:26:15 GMT
Connection: close

gonna start
fmclslvi1p8pmpbnfg8ikfpp3uce5db0ncoms3d4i3tjnbfmrab9nr2cue0to8hra8s87f7r1v2ff2n3c5s68cbqnib3cmn21ddn45k829po4qkgaqkgsdr35uuqqhskvfdj4psldgp58r63g85kbjnn0i53d3sg5kibbe4tsigcavbp2oeee5s63ro68k2eu74t237jghsmtsaocpo771jjtqdh071ogtfp7bel1d6mlj63f88o2adg88uc07l8f62r
fmclslvi1p8pmpbnfg8ikfpp3uce5db0ncoms3d4i3tjnbfmrab9nr2cue0to8hra8s87f7r1v2ff2n3c5s68cbqnib3cmn21ddn45k829po4qkgaqkgsdr35uuqqhskvfdj4psldgp58r63g85kbjnn0i53d3sg5kibbe4tsigcavbp2oeee5s63ro68k2eu74t237jghsmtsaocpo771jjtqdh071ogtfp7bel1d6mlj63f88o2adg88uc07l8f62r
5jf605re18gpuqpvr30gfku1l905edlq7rqrslrh0mkubvlj91crk18htfnbeni3r7c36eukffl04sppprqdco6k23dm0mev9noa5f75frjls40tigeduo2jmfe3f8bneja11nn09giplo0kpn45tnm4etp9jhp5h42gim1ia9lm8s5c6m39gm7h0mcgpj0fogmo2bo319tlgppuhcp6t887s5jvm52fg191mc55cgb7inlir8ail3gbnsdea46vj041
jggsrderm9rpegoq9gapjl4dk14ubc4mb0nfq2bdkqtrdvuihv8q8f0dbqm63n7ojghcchb4c7gbp77011fl8hrfrl0mf9c3mfvhk1acfuofedjido44247ffs8lt28304o8i1luumbnbvbdrqdl8nno4b3t0pul8ep0t6vsgl7bp64pnlfiisepvq1urujtsbbou6batft6ide1qu8ps783qhn07v8n3i2jdj20v599np1ahrkcso9is0g1ja1e31fl
4h1rkt6n478h83db250ldqt517dn40ae5960qmsr5nnsqlv5av2eqmn61sruug2etqjn7h4l5lh2i9i0q1s08d5f6kpmaep8oms77u91gvfop1j2vds6v6o85fbn3cmi27it9l7ogrm305eunsrdgnblhn2bvisa2vkhhi469mj22oklgc3sqcd59eh6e52uhop60vjdq20qcq9up825v446eukk19jmoi2sisnka03kagb7ueaqmdq6rd9lq0g25l20
n1hv30da7d7naqs34r0hgf5r7r75gr8u98vko7krfdogka2d0t0pb7koiuojdm0rn3uc99g9a8epf81e1rkgn98fho2vih003vt759d8asoou9qmnmu5gluejlarbalcf4dk2kic9l9fhhv45vghcuu8tfppo2dapvrnafoetuqlgt4eb6o997iod3fcd5jpfqa47mhnfd5p81fudfcvqej6t69q7hv38nqbgdgtjj73thn534g1j3pc4as8c4dkj8dj
ok we done

您会看到重复的第一个动态生成的行这似乎表明PrintWriter.flush（）方法无法同步。

为什么这不起作用，我能做些什么来实现我的目标？

谢谢。

Answer 1

为了将来参考，我想我可以使用以下代码：

@SuppressWarnings("serial")
public class TestServer extends HttpServlet {
   private final int THREADPOOL_SIZE = 10;
   private ThreadPoolExecutor thread_pool;

   public void init(ServletConfig config) throws ServletException {
      super.init(config);
      thread_pool = (ThreadPoolExecutor) Executors.newFixedThreadPool(THREADPOOL_SIZE);
   }

   public void destroy() {
      thread_pool.shutdownNow();
   }

   public TestServer() {
          super();
   }

   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      CompletionService<String> completion_service_pool = new ExecutorCompletionService<String>(thread_pool);
      int task_num = 10;
      final int line_length = 13000;
      for(int i = 0; i < task_num; i++) {
         completion_service_pool.submit(new Callable<String>(){
            @Override
            public String call() {
               Random rn = new Random();
               int sleep_seconds = Math.abs(rn.nextInt() % 10);
               try {
                  Thread.sleep(sleep_seconds * 1000);
               }
               catch (Exception e) {

               }
               return String.format("Slept for %d seconds. %s<br>\n", sleep_seconds, new BigInteger(line_length, rn).toString(32));
            }
         });
      }

      PrintWriter out = response.getWriter();
      response.setContentType("text/html");
      out.print("gonna start<br>\n");
      out.flush();

      for(int i = 0; i < task_num; ) {
         try {
            Future<String> result_task = completion_service_pool.poll();
            if(result_task != null) {
               String result_string = result_task.get();
               out.print(result_string);
               out.flush();
               i++;
            }
         }
         catch (Exception e) {
         }
      }

      out.print("ok we done<br>\n");
      out.close();
   }
}

JavaEE：在线程中构建和刷新响应

1 个答案: