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PO1s Delay in HttpServer since Java 7
 

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    <p>We are using the internal <code>HttpServer</code> class in a project to exchange data between a client and a server over HTTP. As we switched to Java 7, we realized a delay in the delivery of the results. We could reduce the problem to the following sample:</p> <p>Class <code>EchoServer</code> creates the context <code>/echo</code> which simply returns the current date and the request URI upon each request. This service is then invoked by a client in a loop.</p> <pre><code>import java.io.IOException; import java.io.OutputStream; import java.net.InetSocketAddress; import java.util.Date; import com.sun.net.httpserver.HttpExchange; import com.sun.net.httpserver.HttpHandler; import com.sun.net.httpserver.HttpServer; public class EchoServer { public static void main(String[] args) throws IOException { HttpServer server = HttpServer.create(new InetSocketAddress(80), 0); server.createContext("/echo", new EchoHandler()); server.start(); } static class EchoHandler implements HttpHandler { public void handle(HttpExchange httpExchange) throws IOException { httpExchange.getResponseHeaders().add("Content-type", "text/html"); String response = "&lt;b&gt;" + new Date() + "&lt;/b&gt; for " + httpExchange.getRequestURI(); httpExchange.sendResponseHeaders(200, response.length()); OutputStream os = httpExchange.getResponseBody(); os.write(response.getBytes()); os.close(); } } } </code></pre> <p>The following client invokes the service in an infinite loop using class <code>URL</code> and prints the first character from the returned stream (which will be the <code>&lt;</code> sign). In addition, the client prints the current time.</p> <pre><code>import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; public class EchoClient { public static void main(String[] args) throws Exception{ while(true) { URL url = new URL("http://localhost:80/echo"); BufferedReader rd = new BufferedReader(new InputStreamReader(url.openStream())); int res = rd.read(); System.out.println((char)res); System.out.println(System.currentTimeMillis()); } } } </code></pre> <p>If this code is executed on Java6, everything works fine and a result is printed approx. every 5 ms.</p> <pre><code>% java -version java version "1.6.0_24" Java(TM) SE Runtime Environment (build 1.6.0_24-b07) Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode) % java EchoClient &lt; 1362515635677 &lt; 1362515635682 &lt; 1362515635687 &lt; 1362515635691 </code></pre> <p>If the code is executed on Java7, then each request uses 1000ms approx.</p> <pre><code>% java -version java version "1.7.0_17" Java(TM) SE Runtime Environment (build 1.7.0_17-b02) Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode) % java EchoClient &lt; 1362517297845 &lt; 1362517298844 &lt; 1362517299845 &lt; 1362517300845 </code></pre> <p>It seems that a timeout of 1000ms is hidden somewhere. If the character is read on the <code>InputStreamReader</code> instead over the <code>BufferedReader</code>, the same delay happens. If a byte is read from the input stream directly, then no delay can be seen. On the other hand, if the <code>EchoClient</code> program is run against a servlet, then everything works fine, independent of whether the <code>BufferedReader</code> or the <code>InputStreamReader</code> is used.</p> <p>It seems, that class <code>InputStreamReader</code> is expecting something from the server which is no longer delivered by the Java 7 implementation of HttpServer. Do you have an idea what exactly happens here and how this problem could be resolved? A workaround? Or is this a bug?</p> <p>Thanks!</p> <hr> <p>I have added further timings to the client code:</p> <pre><code>public static void main(String[] args) throws Exception{ while(true) { System.out.println("0: "+System.currentTimeMillis()); URL url = new URL("http://localhost:80/echo"); System.out.println("1: "+System.currentTimeMillis()); InputStream in = url.openStream(); System.out.println("2: "+System.currentTimeMillis()); InputStreamReader isr = new InputStreamReader(in); System.out.println("3: "+System.currentTimeMillis()); char res = (char)isr.read(); // character read is `&lt;` System.out.println(res + ": "+System.currentTimeMillis()); } } </code></pre> <p>with the following result:</p> <pre><code>% java EchoClient 0: 1362532555535 1: 1362532555537 2: 1362532555608 3: 1362532555609 &lt;: 1362532555611 0: 1362532555612 1: 1362532555613 2: 1362532556608 3: 1362532556609 &lt;: 1362532556610 0: 1362532556611 1: 1362532556612 2: 1362532557609 3: 1362532557610 &lt;: 1362532557611 0: 1362532557612 1: 1362532557613 </code></pre> <p>The first invocation of <code>openStream</code> takes some time (70ms), but all further invocations of <code>openStream</code> take much longer (996ms approx).</p>
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    1. COActually, com.sun.net.httpserver is not part of the Java API, and I think it shouldn't be used in mission-critical projects. You can try alternatives such as NanoHTTPD: http://elonen.iki.fi/code/nanohttpd/
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    2. COThis is very interesting but hard to believe. Can you insert more timestamp debugging to find our exactly which part of code takes 1 sec?
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    3. COit is the call to `url.openStream()` which takes 1000ms, but only at its second (and later) invocation in the loop, and only if later an `InputStreamReader` is generated and used to read a byte. Thus, the `BufferedReader` seems to be innocent.
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