[GitHub] [pulsar] heesung-sn commented on pull request #15540: [Fix][broker] Fix JDK17 compatibility issues.

[GitBox <gi...@apache.org>]

heesung-sn commented on PR #15540:
URL: https://github.com/apache/pulsar/pull/15540#issuecomment-1123354744

   Thank you for taking care of this issue. I am wondering if removing reflection could resolve the issue too. Adding `--add-opens` seems radical unless required.
   
   For example, can we directly use the static functions in `InetAddressCachePolicy` for this code?, https://github.com/openjdk/jdk17/blob/master/src/java.base/share/classes/sun/net/InetAddressCachePolicy.java#L154-L160
   
   ```
   static {
           int ttl = DEFAULT_TTL;
           int negativeTtl = DEFAULT_NEGATIVE_TTL;
           try {
               // use reflection to call sun.net.InetAddressCachePolicy's get and getNegative methods for getting
               // effective JDK settings for DNS caching
               Class<?> inetAddressCachePolicyClass = Class.forName("sun.net.InetAddressCachePolicy");
               Method getTTLMethod = inetAddressCachePolicyClass.getMethod("get");
               ttl = (Integer) getTTLMethod.invoke(null);
               Method getNegativeTTLMethod = inetAddressCachePolicyClass.getMethod("getNegative");
               negativeTtl = (Integer) getNegativeTTLMethod.invoke(null);
           } catch (NoSuchMethodException | ClassNotFoundException | InvocationTargetException
                    | IllegalAccessException e) {
               log.warn("Cannot get DNS TTL settings from sun.net.InetAddressCachePolicy class", e);
           }
           TTL = useDefaultTTLWhenSetToForever(ttl, DEFAULT_TTL);
           NEGATIVE_TTL = useDefaultTTLWhenSetToForever(negativeTtl, DEFAULT_NEGATIVE_TTL);
       }
   
   ```
   
   Similarly for this code path, we can use the static functions in `ManagementFactoryHelper`
   https://github.com/openjdk/jdk17/blob/master/src/java.management/share/classes/sun/management/ManagementFactoryHelper.java
   
   
   ```
       private static Method getTotalSafepointTimeHandle;
       private static Method getSafepointCountHandle;
   
       private Map<String, GCMetrics> gcMetricsMap = new HashMap<>();
   
       static {
           try {
               runtime = Class.forName("sun.management.ManagementFactoryHelper")
                       .getMethod("getHotspotRuntimeMBean")
                       .invoke(null);
               getTotalSafepointTimeHandle = runtime.getClass().getMethod("getTotalSafepointTime");
               getTotalSafepointTimeHandle.setAccessible(true);
               getSafepointCountHandle = runtime.getClass().getMethod("getSafepointCount");
               getSafepointCountHandle.setAccessible(true);
   
               // try to use the methods
               getTotalSafepointTimeHandle.invoke(runtime);
               getSafepointCountHandle.invoke(runtime);
           } catch (Throwable e) {
               log.warn("Failed to get Runtime bean", e);
           }
       }
   
   ```
   
   


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