MINOR: Replace some Java 7 style code with Java 8 style (#7623)

Reviewers: Mickael Maison <mickael.maison@gmail.com>, Manikumar Reddy <manikumar.reddy@gmail.com>

clients/src/main/java/org/apache/kafka/common/metrics/JmxReporter.java

@@ -16,30 +16,26 @@
  */
 package org.apache.kafka.common.metrics;
 
-import java.lang.management.ManagementFactory;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.MetricName;
+import org.apache.kafka.common.utils.Sanitizer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.management.Attribute;
 import javax.management.AttributeList;
 import javax.management.AttributeNotFoundException;
 import javax.management.DynamicMBean;
-import javax.management.InvalidAttributeValueException;
 import javax.management.JMException;
 import javax.management.MBeanAttributeInfo;
-import javax.management.MBeanException;
 import javax.management.MBeanInfo;
 import javax.management.MBeanServer;
 import javax.management.MalformedObjectNameException;
 import javax.management.ObjectName;
-import javax.management.ReflectionException;
-
-import org.apache.kafka.common.KafkaException;
-import org.apache.kafka.common.MetricName;
-import org.apache.kafka.common.utils.Sanitizer;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import java.lang.management.ManagementFactory;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 /**
  * Register metrics in JMX as dynamic mbeans based on the metric names
@@ -49,7 +45,7 @@ public class JmxReporter implements MetricsReporter {
     private static final Logger log = LoggerFactory.getLogger(JmxReporter.class);
     private static final Object LOCK = new Object();
     private String prefix;
-    private final Map<String, KafkaMbean> mbeans = new HashMap<String, KafkaMbean>();
+    private final Map<String, KafkaMbean> mbeans = new HashMap<>();
 
     public JmxReporter() {
         this("");
@@ -175,7 +171,7 @@ public class JmxReporter implements MetricsReporter {
         private final ObjectName objectName;
         private final Map<String, KafkaMetric> metrics;
 
-        public KafkaMbean(String mbeanName) throws MalformedObjectNameException {
+        KafkaMbean(String mbeanName) throws MalformedObjectNameException {
             this.metrics = new HashMap<>();
             this.objectName = new ObjectName(mbeanName);
         }
@@ -184,12 +180,12 @@ public class JmxReporter implements MetricsReporter {
             return objectName;
         }
 
-        public void setAttribute(String name, KafkaMetric metric) {
+        void setAttribute(String name, KafkaMetric metric) {
             this.metrics.put(name, metric);
         }
 
         @Override
-        public Object getAttribute(String name) throws AttributeNotFoundException, MBeanException, ReflectionException {
+        public Object getAttribute(String name) throws AttributeNotFoundException {
             if (this.metrics.containsKey(name))
                 return this.metrics.get(name).metricValue();
             else
@@ -209,7 +205,7 @@ public class JmxReporter implements MetricsReporter {
             return list;
         }
 
-        public KafkaMetric removeAttribute(String name) {
+        KafkaMetric removeAttribute(String name) {
             return this.metrics.remove(name);
         }
 
@@ -232,15 +228,12 @@ public class JmxReporter implements MetricsReporter {
         }
 
         @Override
-        public Object invoke(String name, Object[] params, String[] sig) throws MBeanException, ReflectionException {
+        public Object invoke(String name, Object[] params, String[] sig) {
             throw new UnsupportedOperationException("Set not allowed.");
         }
 
         @Override
-        public void setAttribute(Attribute attribute) throws AttributeNotFoundException,
-                                                     InvalidAttributeValueException,
-                                                     MBeanException,
-                                                     ReflectionException {
+        public void setAttribute(Attribute attribute) {
             throw new UnsupportedOperationException("Set not allowed.");
         }
 

clients/src/main/java/org/apache/kafka/common/metrics/Metrics.java

@@ -38,7 +38,6 @@ import java.util.TreeMap;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
-import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
 import static java.util.Collections.emptyList;
@@ -137,29 +136,20 @@ public class Metrics implements Closeable {
         this.reporters = Objects.requireNonNull(reporters);
         this.time = time;
         for (MetricsReporter reporter : reporters)
-            reporter.init(new ArrayList<KafkaMetric>());
+            reporter.init(new ArrayList<>());
 
         // Create the ThreadPoolExecutor only if expiration of Sensors is enabled.
         if (enableExpiration) {
             this.metricsScheduler = new ScheduledThreadPoolExecutor(1);
             // Creating a daemon thread to not block shutdown
-            this.metricsScheduler.setThreadFactory(new ThreadFactory() {
-                public Thread newThread(Runnable runnable) {
-                    return KafkaThread.daemon("SensorExpiryThread", runnable);
-                }
-            });
+            this.metricsScheduler.setThreadFactory(runnable -> KafkaThread.daemon("SensorExpiryThread", runnable));
             this.metricsScheduler.scheduleAtFixedRate(new ExpireSensorTask(), 30, 30, TimeUnit.SECONDS);
         } else {
             this.metricsScheduler = null;
         }
 
         addMetric(metricName("count", "kafka-metrics-count", "total number of registered metrics"),
-            new Measurable() {
-                @Override
-                public double measure(MetricConfig config, long now) {
-                    return metrics.size();
-                }
-            });
+            (config, now) -> metrics.size());
     }
 
     /**
@@ -186,7 +176,7 @@ public class Metrics implements Closeable {
      * @param description A human-readable description to include in the metric
      */
     public MetricName metricName(String name, String group, String description) {
-        return metricName(name, group, description, new HashMap<String, String>());
+        return metricName(name, group, description, new HashMap<>());
     }
 
     /**
@@ -196,7 +186,7 @@ public class Metrics implements Closeable {
      * @param group       logical group name of the metrics to which this metric belongs
      */
     public MetricName metricName(String name, String group) {
-        return metricName(name, group, "", new HashMap<String, String>());
+        return metricName(name, group, "", new HashMap<>());
     }
 
     /**
@@ -227,7 +217,7 @@ public class Metrics implements Closeable {
     private static Map<String, String> getTags(String... keyValue) {
         if ((keyValue.length % 2) != 0)
             throw new IllegalArgumentException("keyValue needs to be specified in pairs");
-        Map<String, String> tags = new LinkedHashMap<String, String>();
+        Map<String, String> tags = new LinkedHashMap<>();
 
         for (int i = 0; i < keyValue.length; i += 2)
             tags.put(keyValue[i], keyValue[i + 1]);
@@ -245,7 +235,7 @@ public class Metrics implements Closeable {
      * @return the string containing the HTML table; never null
      */
     public static String toHtmlTable(String domain, Iterable<MetricNameTemplate> allMetrics) {
-        Map<String, Map<String, String>> beansAndAttributes = new TreeMap<String, Map<String, String>>();
+        Map<String, Map<String, String>> beansAndAttributes = new TreeMap<>();
     
         try (Metrics metrics = new Metrics()) {
             for (MetricNameTemplate template : allMetrics) {
@@ -257,7 +247,7 @@ public class Metrics implements Closeable {
                 MetricName metricName = metrics.metricName(template.name(), template.group(), template.description(), tags);
                 String mBeanName = JmxReporter.getMBeanName(domain, metricName);
                 if (!beansAndAttributes.containsKey(mBeanName)) {
-                    beansAndAttributes.put(mBeanName, new TreeMap<String, String>());
+                    beansAndAttributes.put(mBeanName, new TreeMap<>());
                 }
                 Map<String, String> attrAndDesc = beansAndAttributes.get(mBeanName);
                 if (!attrAndDesc.containsKey(template.name())) {
@@ -405,11 +395,7 @@ public class Metrics implements Closeable {
             this.sensors.put(name, s);
             if (parents != null) {
                 for (Sensor parent : parents) {
-                    List<Sensor> children = childrenSensors.get(parent);
-                    if (children == null) {
-                        children = new ArrayList<>();
-                        childrenSensors.put(parent, children);
-                    }
+                    List<Sensor> children = childrenSensors.computeIfAbsent(parent, k -> new ArrayList<>());
                     children.add(s);
                 }
             }