Use a real HTTP server in tests for the HTTP client

If we open a socket and just close it, the client could not consider
it a server at all and won't throw a NoHttpResponseException.

metrics-httpclient/src/test/java/com/codahale/metrics/httpclient/InstrumentedHttpClientsTest.java

@@ -3,17 +3,16 @@
 import com.codahale.metrics.MetricRegistry;
 import com.codahale.metrics.MetricRegistryListener;
 import com.codahale.metrics.Timer;
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpServer;
 import org.apache.http.HttpRequest;
 import org.apache.http.NoHttpResponseException;
 import org.apache.http.client.HttpClient;
 import org.apache.http.client.methods.HttpGet;
 import org.junit.Before;
 import org.junit.Test;
 
-import java.io.IOException;
 import java.net.InetSocketAddress;
-import java.net.ServerSocket;
-import java.net.Socket;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
@@ -52,21 +51,14 @@ public void registersExpectedMetricsGivenNameStrategy() throws Exception {
 
     @Test
     public void registersExpectedExceptionMetrics() throws Exception {
-        ServerSocket server = new ServerSocket();
-        server.bind(new InetSocketAddress("localhost", 0));
-        final HttpGet get = new HttpGet("http://localhost:" + server.getLocalPort() + "/");
+        HttpServer httpServer = HttpServer.create(new InetSocketAddress(0), 0);
+
+        final HttpGet get = new HttpGet("http://localhost:" + httpServer.getAddress().getPort() + "/");
         final String requestMetricName = "request";
         final String exceptionMetricName = "exception";
 
-        Thread serverThread = new Thread(() -> {
-            try {
-                final Socket socket = server.accept();
-                socket.close();
-            } catch (IOException e) {
-                e.printStackTrace();
-            }
-        });
-        serverThread.start();
+        httpServer.createContext("/", HttpExchange::close);
+        httpServer.start();
 
         when(metricNameStrategy.getNameFor(any(), any(HttpRequest.class)))
                 .thenReturn(requestMetricName);
@@ -79,8 +71,7 @@ public void registersExpectedExceptionMetrics() throws Exception {
         } catch (NoHttpResponseException expected) {
             assertThat(metricRegistry.getMeters()).containsKey("exception");
         } finally {
-            serverThread.interrupt();
-            serverThread.join();
+            httpServer.stop(0);
         }
     }
 }