Servlet seems to handle multiple concurrent browser requests synchronously

Question

As far as I know Java Servlets are handling multiple requests concurrently and I've searched through StackOverflow as well as Google, and confirmed what I thought. However I am quite confused right now, I wrote a simple servlets that seem to show blocking behaviour.

so I have a simple Servlet:

public class MyServlet extends HttpServlet { private static final long serialVersionUID = 2628320200587071622L; private static final Logger logger = Logger.getLogger(MyServlet.class); @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { logger.info("[doGet] Test before"); try { Thread.sleep(60000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } logger.info("[doGet] Test after"); resp.setContentType("text/plain"); resp.getWriter().write("OK"); } }

Then I have 2 browser windows, I opened at the same time that hit my Servlet. And the result is the first request blocking the 2nd one. The log also shows:

10:49:05,088 [http-8383-Processor14] INFO MyServlet - [doGet] Test before 10:50:05,096 [http-8383-Processor14] INFO MyServlet - [doGet] Test after 10:50:05,106 [http-8383-Processor22] INFO MyServlet - [doGet] Test before 10:51:05,112 [http-8383-Processor22] INFO MyServlet - [doGet] Test after

I feel like I am missing something ... Servlets supposed to be able to handle concurrent request, but it doesnt seem to be doing it. I also did the same as above on the service method instead of doGet and it does the same thing.

Any pointers?

Thanks

Your browser might serialise the requests, what happens if you try this from 2 different computers or with 2 different browsers? (i.e. iexploere and firefox) You can also check http access logs to see if requests arrive at your servlet container concurrently. — rsp
– rsp, Commented Nov 4, 2011 at 15:02
Can you show the web.xml and (assuming this is tomcat) the server.xml. — beny23
– beny23, Commented Nov 4, 2011 at 15:10
@beny: I'm not sure how exactly that would be helpful in understanding the cause of the problem. Can you elaborate? — BalusC
– BalusC, Commented Nov 4, 2011 at 15:15
@BalusC: Just for completeness really, maybe there would have been just the one worker thread (unlikely due to the log category http-8383-Processor14 and 22), or some esotheric filter in web.xml... — beny23
– beny23, Commented Nov 4, 2011 at 15:37

BalusC · Accepted Answer · 2016-03-02 22:47:34Z

39

Your browser is apparently using the same HTTP connection in different windows. The servlet container uses a single thread per HTTP connection, not per HTTP request. You should run two physically different webbrowsers to test this properly. E.g. one Firefox and one Chrome.

edited Mar 2, 2016 at 22:47

answered Nov 4, 2011 at 15:01

BalusC

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2 Comments

Luigi Cortese Over a year ago

What makes you think that a single-thread-per-connection is being used here? The two requests are processed by different threads, couldn't it be that a single-thread-per-request policy is actually adopted by the server, whereas at client side the same TCP connection is being used without HTTP pipelining (so queued by the browser)? This would explain the sequential processing despite different threads involved

Farhan stands with Palestine Over a year ago

@BalusC: Instead of polluting this thread, I considered raising a separate thread for this. Please see - stackoverflow.com/questions/37360731/…

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