8371092: NullPointerException in AltServiceUsageTest.afterClass() test

Reviewed-by: dfuchs

Author: PeyaPeyaPeyang

test/jdk/java/net/httpclient/AltServiceUsageTest.java

@@ -123,7 +123,7 @@ private void createServers() throws IOException {
     public void afterClass() throws Exception {
         safeStop(originServer);
         safeStop(altServer);
-        udpNotResponding.close();
+        safeClose(udpNotResponding);
     }
 
     private static void safeStop(final HttpTestServer server) {
@@ -140,6 +140,19 @@ private static void safeStop(final HttpTestServer server) {
         }
     }
 
+    private static void safeClose(final DatagramChannel channel) {
+        if (channel == null) {
+            return;
+        }
+        try {
+            System.out.println("Closing DatagramChannel " + channel.getLocalAddress());
+            channel.close();
+        } catch (Exception e) {
+            System.err.println("Ignoring exception: " + e.getMessage() + " that occurred " +
+                    "during close of DatagramChannel: " + channel);
+        }
+    }
+
     private static class H3AltServicePublisher implements HttpTestHandler {
         private static final String RESPONSE_CONTENT = "apple";