Add support for patterns in MBean object names

metrics-core/src/main/java/com/codahale/metrics/JmxAttributeGauge.java

@@ -5,6 +5,7 @@
 import javax.management.MBeanServerConnection;
 import javax.management.ObjectName;
 import java.lang.management.ManagementFactory;
+import java.util.Set;
 
 /**
  * A {@link Gauge} implementation which queries an {@link MBeanServerConnection} for an attribute of an object.
@@ -40,11 +41,21 @@ public JmxAttributeGauge(MBeanServerConnection mBeanServerConn, ObjectName objec
     @Override
     public Object getValue() {
         try {
-            return mBeanServerConn.getAttribute(objectName, attributeName);
+            return mBeanServerConn.getAttribute(getObjectName(), attributeName);
         } catch (IOException e) {
             return null;
         } catch (JMException e) {
             return null;
         }
     }
+
+    private ObjectName getObjectName() throws IOException {
+        if (objectName.isPattern()) {
+            Set<ObjectName> foundNames = mBeanServerConn.queryNames(objectName, null);
+            if (foundNames.size() == 1) {
+                return foundNames.iterator().next();
+            }
+        }
+        return objectName;
+    }
 }

metrics-core/src/test/java/com/codahale/metrics/JmxAttributeGaugeTest.java

@@ -1,34 +1,99 @@
 package com.codahale.metrics;
 
-import org.junit.Test;
+import static org.assertj.core.api.Assertions.assertThat;
 
-import javax.management.AttributeNotFoundException;
+import java.lang.management.ManagementFactory;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.management.JMException;
 import javax.management.MBeanServer;
+import javax.management.ObjectInstance;
 import javax.management.ObjectName;
 
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
 
 public class JmxAttributeGaugeTest {
-    private final MBeanServer mBeanServer = mock(MBeanServer.class);
-    private final ObjectName objectName = mock(ObjectName.class);
-    private final JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "attr");
-    private final Object value = mock(Object.class);
+
+    private static MBeanServer mBeanServer = ManagementFactory.getPlatformMBeanServer();
+
+    private static List<ObjectName> registeredMBeans = new ArrayList<ObjectName>();
+
+    public interface JmxTestMBean {
+        Long getValue();
+    }
+
+    private static class JmxTest implements JmxTestMBean {
+        @Override
+        public Long getValue() {
+            return Long.MAX_VALUE;
+        }
+    }
+
+    @BeforeClass
+    public static void setUp() throws Exception {
+        registerMBean(new ObjectName("JmxAttributeGaugeTest:type=test,name=test1"));
+        registerMBean(new ObjectName("JmxAttributeGaugeTest:type=test,name=test2"));
+    }
+
+    @AfterClass
+    public static void tearDown() {
+        for (ObjectName objectName : registeredMBeans) {
+            try {
+                mBeanServer.unregisterMBean(objectName);
+            } catch (Exception e) {
+                // ignore
+            }
+        }
+    }
 
     @Test
-    public void returnsAJmxAttribute() throws Exception {
-        when(mBeanServer.getAttribute(objectName, "attr")).thenReturn(value);
+    public void returnsJmxAttribute() throws Exception {
+        ObjectName objectName = new ObjectName("java.lang:type=ClassLoading");
+        JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "LoadedClassCount");
 
-        assertThat(gauge.getValue())
-                .isEqualTo(value);
+        assertThat(gauge.getValue()).isInstanceOf(Integer.class);
+        assertThat((Integer) gauge.getValue()).isGreaterThan(0);
     }
 
     @Test
-    public void returnsNullIfThereIsAnException() throws Exception {
-        when(mBeanServer.getAttribute(objectName, "attr")).thenThrow(new AttributeNotFoundException());
+    public void returnsNullIfAttributeDoesNotExist() throws Exception {
+        ObjectName objectName = new ObjectName("java.lang:type=ClassLoading");
+        JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "DoesNotExist");
 
-        assertThat(gauge.getValue())
-                .isNull();
+        assertThat(gauge.getValue()).isNull();
     }
+
+    @Test
+    public void returnsNullIfMBeanNotFound() throws Exception {
+        ObjectName objectName = new ObjectName("foo.bar:type=NoSuchMBean");
+        JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "LoadedClassCount");
+
+        assertThat(gauge.getValue()).isNull();
+    }
+
+    @Test
+    public void returnsAttributeForObjectNamePattern() throws Exception {
+        ObjectName objectName = new ObjectName("JmxAttributeGaugeTest:name=test1,*");
+        JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "Value");
+
+        assertThat(gauge.getValue()).isInstanceOf(Long.class);
+        assertThat((Long) gauge.getValue()).isEqualTo(Long.MAX_VALUE);
+    }
+
+    @Test
+    public void returnsNullIfObjectNamePatternAmbiguous() throws Exception {
+        ObjectName objectName = new ObjectName("JmxAttributeGaugeTest:type=test,*");
+        JmxAttributeGauge gauge = new JmxAttributeGauge(mBeanServer, objectName, "Value");
+
+        assertThat(gauge.getValue()).isNull();
+    }
+
+    private static void registerMBean(ObjectName objectName) throws JMException {
+        ObjectInstance objectInstance = mBeanServer.registerMBean(new JmxTest(), objectName);
+        registeredMBeans.add(objectInstance.getObjectName());
+    }
+
 }