[fix][cli] Fix mbeans to json

bin/pulsar

@@ -300,8 +300,11 @@ if [[ -z "$IS_JAVA_8" ]]; then
   # https://github.com/netty/netty/issues/12265
   OPTS="$OPTS --add-opens java.base/java.nio=ALL-UNNAMED --add-opens java.base/jdk.internal.misc=ALL-UNNAMED"
   # netty.DnsResolverUtil
-  # JvmDefaultGCMetricsLogger
-  OPTS="$OPTS --add-opens java.base/sun.net=ALL-UNNAMED --add-opens java.management/sun.management=ALL-UNNAMED"
+  OPTS="$OPTS --add-opens java.base/sun.net=ALL-UNNAMED"
+  # JvmDefaultGCMetricsLogger & MBeanStatsGenerator
+  OPTS="$OPTS --add-opens java.management/sun.management=ALL-UNNAMED"
+  # MBeanStatsGenerator
+  OPTS="$OPTS --add-opens jdk.management/com.sun.management.internal=ALL-UNNAMED"
 fi
 
 OPTS="-cp $PULSAR_CLASSPATH $OPTS"

pom.xml

@@ -98,7 +98,8 @@ flexible messaging model and an intuitive client API.</description>
       --add-opens java.base/java.io=ALL-UNNAMED <!--Bookkeeper NativeIO-->
       --add-opens java.base/java.util=ALL-UNNAMED <!--System Lambda-->
       --add-opens java.base/sun.net=ALL-UNNAMED <!--netty.DnsResolverUtil-->
-      --add-opens java.management/sun.management=ALL-UNNAMED <!--JvmDefaultGCMetricsLogger-->
+      --add-opens java.management/sun.management=ALL-UNNAMED <!--JvmDefaultGCMetricsLogger & MBeanStatsGenerator-->
+      --add-opens jdk.management/com.sun.management.internal=ALL-UNNAMED <!--MBeanStatsGenerator-->
     </test.additional.args>
     <testReuseFork>true</testReuseFork>
     <testForkCount>4</testForkCount>

pulsar-broker/src/test/java/org/apache/pulsar/broker/admin/BrokerStatTest.java

@@ -0,0 +1,50 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.admin;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.pulsar.broker.auth.MockedPulsarServiceBaseTest;
+import org.apache.pulsar.client.admin.PulsarAdminException;
+import org.apache.pulsar.common.util.ObjectMapperFactory;
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.Test;
+
+@Slf4j
+@Test(groups = "broker-admin")
+public class BrokerStatTest extends MockedPulsarServiceBaseTest {
+    @BeforeMethod
+    @Override
+    public void setup() throws Exception {
+        super.internalSetup();
+    }
+
+    @AfterMethod(alwaysRun = true)
+    @Override
+    public void cleanup() throws Exception {
+        super.internalCleanup();
+    }
+
+    @Test
+    public void testGetMBeans() throws PulsarAdminException, JsonProcessingException {
+        String data = admin.brokerStats().getMBeans();
+        ObjectMapperFactory.create().readTree(data);
+    }
+}