Fixes #3090 - MBeanContainer throws NPE for arrays.

Corrected places that were making unguarded calls to Class.getPackage().
Added tests for various array cases.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-jmx/src/main/java/org/eclipse/jetty/jmx/MBeanContainer.java

@@ -217,8 +217,11 @@ public class MBeanContainer implements Container.InheritedListener, Dumpable, De
 
     private static Constructor<?> findConstructor(Class<?> klass)
     {
-        String pName = klass.getPackage().getName();
-        String cName = klass.getName().substring(pName.length() + 1);
+        Package pkg = klass.getPackage();
+        if (pkg == null)
+            return null;
+        String pName = pkg.getName();
+        String cName = klass.getName().substring(pName.isEmpty() ? 0 : pName.length() + 1);
         String mName = pName + ".jmx." + cName + "MBean";
         try
         {
@@ -310,12 +313,19 @@ public class MBeanContainer implements Container.InheritedListener, Dumpable, De
             // No override of the mbean's ObjectName, so make a generic one.
             if (objectName == null)
             {
+                Class<?> klass = obj.getClass();
+                while (klass.isArray())
+                    klass = klass.getComponentType();
+
                 // If no explicit domain, create one.
                 String domain = _domain;
                 if (domain == null)
-                    domain = obj.getClass().getPackage().getName();
+                {
+                    Package pkg = klass.getPackage();
+                    domain = pkg == null ? "" : pkg.getName();
+                }
 
-                String type = obj.getClass().getName().toLowerCase(Locale.ENGLISH);
+                String type = klass.getName().toLowerCase(Locale.ENGLISH);
                 int dot = type.lastIndexOf('.');
                 if (dot >= 0)
                     type = type.substring(dot + 1);

jetty-jmx/src/test/java/org/eclipse/jetty/jmx/ObjectMBeanTest.java

@@ -24,6 +24,7 @@ import javax.management.Attribute;
 import javax.management.MBeanInfo;
 import javax.management.MBeanOperationInfo;
 import javax.management.MBeanParameterInfo;
+import javax.management.ObjectName;
 
 import com.acme.Derived;
 import com.acme.Managed;
@@ -34,6 +35,7 @@ import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -54,6 +56,46 @@ public class ObjectMBeanTest
         container = null;
     }
 
+    @Test
+    public void testMBeanForNull()
+    {
+        Object mBean = container.mbeanFor(null);
+        assertNull(mBean);
+    }
+
+    @Test
+    public void testMBeanForString()
+    {
+        String obj = "foo";
+        Object mbean = container.mbeanFor(obj);
+        assertNotNull(mbean);
+        container.beanAdded(null, obj);
+        ObjectName objectName = container.findMBean(obj);
+        assertNotNull(objectName);
+    }
+
+    @Test
+    public void testMBeanForStringArray()
+    {
+        String[] obj = {"a", "b"};
+        Object mbean = container.mbeanFor(obj);
+        assertNotNull(mbean);
+        container.beanAdded(null, obj);
+        ObjectName objectName = container.findMBean(obj);
+        assertNotNull(objectName);
+    }
+
+    @Test
+    public void testMBeanForIntArray()
+    {
+        int[] obj = {0, 1, 2};
+        Object mbean = container.mbeanFor(obj);
+        assertNotNull(mbean);
+        container.beanAdded(null, obj);
+        ObjectName objectName = container.findMBean(obj);
+        assertNotNull(objectName);
+    }
+
     @Test
     public void testMetaDataCaching()
     {

jetty-jmx/src/test/java/org/eclipse/jetty/jmx/ObjectMBeanUtilTest.java

@@ -70,13 +70,6 @@ public class ObjectMBeanUtilTest
         assertEquals("Test the mbean extended stuff", objectMBeanInfo.getDescription(), "Mbean description must be equal to : Test the mbean extended stuff");
     }
 
-    @Test
-    public void testMbeanForNullCheck()
-    {
-        Object mBean = container.mbeanFor(null);
-        assertNull(mBean, "As we are passing null value the output should be null");
-    }
-
     @Test
     public void testGetAttributeMBeanException() throws Exception
     {
@@ -151,7 +144,7 @@ public class ObjectMBeanUtilTest
     }
 
     @Test
-    public void testSetAttributesForCollectionTypeAttribue() throws Exception
+    public void testSetAttributesForCollectionTypeAttribute() throws Exception
     {
         ArrayList<Derived> aliasNames = new ArrayList<>(Arrays.asList(getArrayTypeAttribute()));
 
@@ -231,7 +224,7 @@ public class ObjectMBeanUtilTest
         ReflectionException e = assertThrows(ReflectionException.class, () ->
                 objectMBean.invoke("good", new Object[0], new String[]{"int aone"}));
 
-        assertNotNull(e, "An ReflectionException must have occurred by now as we cannot call a methow with wrong signature");
+        assertNotNull(e, "A ReflectionException must have occurred by now as we cannot call a method with wrong signature");
     }
 
     @Test