Give a better error message if the JMX bean name is incorrect

Author: amckenzie

CHANGELOG.md

@@ -5,6 +5,9 @@ on [Keep a CHANGELOG](http://keepachangelog.com/). This project adheres to
 
 
 ## [Unreleased]
+## [6.0.8] - 2019-08-21
+### Fixed
+- Better error message if the name of the JMX bean is incorrect when called by the client
 
 ## [6.0.7] - 2019-08-20
 ### Added

jmx/jmx-command-client/src/main/java/uk/gov/justice/services/jmx/system/command/client/MBeanClientException.java

@@ -2,6 +2,10 @@
 
 public class MBeanClientException extends RuntimeException {
 
+    public MBeanClientException(final String message) {
+        super(message);
+    }
+
     public MBeanClientException(final String message, final Throwable cause) {
         super(message, cause);
     }

jmx/jmx-command-client/src/main/java/uk/gov/justice/services/jmx/system/command/client/connection/MBeanConnector.java

@@ -25,7 +25,12 @@ public <T> T connect(final String contextName, final Class<T> mBeanInterface, fi
             final ObjectName objectName = commandMBeanNameProvider.create(contextName);
             final MBeanServerConnection connection = jmxConnector.getMBeanServerConnection();
 
-            return remoteMBeanFactory.createRemote(connection, objectName, mBeanInterface);
+            if(connection.isRegistered(objectName)) {
+                return remoteMBeanFactory.createRemote(connection, objectName, mBeanInterface);
+            }
+
+            throw new MBeanClientException(format("No JMX bean found with name '%s'. Is your context name of '%s' correct?", objectName.getKeyProperty("type"), contextName));
+
         } catch (final IOException e) {
             throw new MBeanClientException(format("Failed to get remote connection to MBean '%s'", mBeanInterface.getSimpleName()), e);
         }

jmx/jmx-command-client/src/test/java/uk/gov/justice/services/jmx/system/command/client/connection/MBeanConnectorTest.java

@@ -5,10 +5,13 @@
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
+import static uk.gov.justice.services.test.utils.core.reflection.ReflectionUtil.setField;
 
 import uk.gov.justice.services.jmx.api.mbean.SystemCommanderMBean;
 import uk.gov.justice.services.jmx.api.name.CommandMBeanNameProvider;
+import uk.gov.justice.services.jmx.api.name.ObjectNameFactory;
 import uk.gov.justice.services.jmx.system.command.client.MBeanClientException;
+import uk.gov.justice.services.test.utils.core.reflection.ReflectionUtil;
 
 import java.io.IOException;
 
@@ -47,6 +50,7 @@ public void shouldConnectToARemoteInstanceOfTheJmxBean() throws Exception {
 
         when(commandMBeanNameProvider.create(contextName)).thenReturn(objectName);
         when(jmxConnector.getMBeanServerConnection()).thenReturn(connection);
+        when(connection.isRegistered(objectName)).thenReturn(true);
         when(remoteMBeanFactory.createRemote(connection, objectName, mBeanInterface)).thenReturn(systemCommanderMBean);
 
         assertThat(mBeanConnector.connect(contextName, mBeanInterface, jmxConnector), is(systemCommanderMBean));
@@ -74,4 +78,34 @@ public void shouldThrowExceptionIfConnectingToTheMBeanFails() throws Exception {
             assertThat(expected.getMessage(), is("Failed to get remote connection to MBean 'SystemCommanderMBean'"));
         }
     }
+
+    @Test
+    public void shouldThrowExceptionIfMBeanNameNotCorrect() throws Exception {
+
+        final String contextName = "people";
+        final ObjectName realObjectName = createARealObjectName(contextName);
+
+        final Class<SystemCommanderMBean> mBeanInterface = SystemCommanderMBean.class;
+        final JMXConnector jmxConnector =  mock(JMXConnector.class);
+        final MBeanServerConnection connection = mock(MBeanServerConnection.class);
+
+        when(commandMBeanNameProvider.create(contextName)).thenReturn(realObjectName);
+        when(jmxConnector.getMBeanServerConnection()).thenReturn(connection);
+        when(connection.isRegistered(realObjectName)).thenReturn(false);
+
+
+        try {
+            mBeanConnector.connect(contextName, mBeanInterface, jmxConnector);
+            fail();
+        } catch (final MBeanClientException expected) {
+            assertThat(expected.getMessage(), is("No JMX bean found with name 'people-system-command-handler-mbean'. Is your context name of 'people' correct?"));
+        }
+    }
+
+    private ObjectName createARealObjectName(final String contextName) {
+        final CommandMBeanNameProvider commandMBeanNameProvider = new CommandMBeanNameProvider();
+        setField(commandMBeanNameProvider, "objectNameFactory", new ObjectNameFactory());
+
+        return commandMBeanNameProvider.create(contextName);
+    }
 }