HDFS-15100. RBF: Print stacktrace when DFSRouter fails to fetch/parse JMX output from NameNode. (#1800)

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/FederationUtil.java

@@ -98,13 +98,14 @@ public final class FederationUtil {
       JSONObject json = new JSONObject(jmxOutput);
       ret = json.getJSONArray("beans");
     } catch (IOException e) {
-      LOG.error("Cannot read JMX bean {} from server {}: {}",
-          beanQuery, webAddress, e.getMessage());
+      LOG.error("Cannot read JMX bean {} from server {}",
+          beanQuery, webAddress, e);
     } catch (JSONException e) {
+      // We shouldn't need more details if the JSON parsing fails.
       LOG.error("Cannot parse JMX output for {} from server {}: {}",
           beanQuery, webAddress, e.getMessage());
     } catch (Exception e) {
-      LOG.error("Cannot parse JMX output for {} from server {}: {}",
+      LOG.error("Cannot parse JMX output for {} from server {}",
           beanQuery, webAddress, e);
     } finally {
       if (reader != null) {