[FLINK-23658][metrics][jmx] Cleanup code

flink-metrics/flink-metrics-jmx/src/main/java/org/apache/flink/metrics/jmx/JMXReporter.java

@@ -62,13 +62,7 @@ public class JMXReporter implements MetricReporter {
 
  private static final Logger LOG = LoggerFactory.getLogger(JMXReporter.class);
 
- private static final CharacterFilter CHARACTER_FILTER =
- new CharacterFilter() {
- @Override
- public String filterCharacters(String input) {
- return replaceInvalidChars(input);
- }
- };
+ private static final CharacterFilter CHARACTER_FILTER = JMXReporter::replaceInvalidChars;
 
  // ------------------------------------------------------------------------
 
@@ -120,7 +114,7 @@ public void notifyOfAddedMetric(Metric metric, String metricName, MetricGroup gr
  try {
  jmxName = new ObjectName(domain, table);
  } catch (MalformedObjectNameException e) {
- /**
+ /*
  * There is an implementation error on our side if this occurs. Either the domain was
  * modified and no longer conforms to the JMX domain rules or the table wasn't properly
  * generated.
@@ -278,7 +272,7 @@ public interface JmxCounterMBean extends MetricMBean {
  }
 
  private static class JmxCounter extends AbstractBean implements JmxCounterMBean {
- private Counter counter;
+ private final Counter counter;
 
  JmxCounter(Counter counter) {
  this.counter = counter;
@@ -310,6 +304,7 @@ public Object getValue() {
  }
 
  /** The MBean interface for an exposed histogram. */
+ @SuppressWarnings("unused")
  public interface JmxHistogramMBean extends MetricMBean {
  long getCount();
 

flink-metrics/flink-metrics-jmx/src/test/java/org/apache/flink/metrics/jmx/JMXReporterTest.java

@@ -138,15 +138,11 @@ public void testPortConflictHandling() throws Exception {
  rep1.notifyOfRemovedMetric(g2, "rep2", null);
  }
 
- /**
- * Verifies that we can connect to multiple JMXReporters running on the same machine.
- *
- * @throws Exception
- */
+ /** Verifies that we can connect to multiple JMXReporters running on the same machine. */
  @Test
  public void testJMXAvailability() throws Exception {
- final MetricReporter rep1 = new JMXReporter("9040-9055");
- final MetricReporter rep2 = new JMXReporter("9040-9055");
+ final JMXReporter rep1 = new JMXReporter("9040-9055");
+ final JMXReporter rep2 = new JMXReporter("9040-9055");
 
  Gauge<Integer> g1 = () -> 1;
  Gauge<Integer> g2 = () -> 2;
@@ -166,9 +162,9 @@ public void testJMXAvailability() throws Exception {
  JMXServiceURL url1 =
  new JMXServiceURL(
  "service:jmx:rmi:https://localhost:"
- + ((JMXReporter) rep1).getPort().get()
+ + rep1.getPort().get()
  + "/jndi/rmi:https://localhost:"
- + ((JMXReporter) rep1).getPort().get()
+ + rep1.getPort().get()
  + "/jmxrmi");
  JMXConnector jmxCon1 = JMXConnectorFactory.connect(url1);
  MBeanServerConnection mCon1 = jmxCon1.getMBeanServerConnection();
@@ -181,9 +177,9 @@ public void testJMXAvailability() throws Exception {
  JMXServiceURL url2 =
  new JMXServiceURL(
  "service:jmx:rmi:https://localhost:"
- + ((JMXReporter) rep2).getPort().get()
+ + rep2.getPort().get()
  + "/jndi/rmi:https://localhost:"
- + ((JMXReporter) rep2).getPort().get()
+ + rep2.getPort().get()
  + "/jmxrmi");
  JMXConnector jmxCon2 = JMXConnectorFactory.connect(url2);
  MBeanServerConnection mCon2 = jmxCon2.getMBeanServerConnection();