flozano · March 24, 2022 10:23 · Jan 15, 2016
diff --git a/MonBuffers.java b/MonBuffers.java
@@ -0,0 +1,65 @@
+import java.io.File;
+import java.util.*;
+import java.lang.management.BufferPoolMXBean;
+import java.lang.management.ManagementFactory;
+import javax.management.MBeanServerConnection;
+import javax.management.ObjectName;
+import javax.management.remote.*;
+
+import com.sun.tools.attach.VirtualMachine; // Attach API
+
+/**
+ * Simple tool to attach to running VM to report buffer pool usage.
+ */
+
+public class MonBuffers {
+    static final String CONNECTOR_ADDRESS =
+          "com.sun.management.jmxremote.localConnectorAddress";
+
+    public static void main(String args[]) throws Exception {
+        // attach to target VM to get connector address
+        VirtualMachine vm = VirtualMachine.attach(args[0]);
+        String connectorAddress = vm.getAgentProperties().getProperty(CONNECTOR_ADDRESS);
+        if (connectorAddress == null) {
+            // start management agent
+            String agent = vm.getSystemProperties().getProperty("java.home") +
+                    File.separator + "lib" + File.separator + "management-agent.jar";
+            vm.loadAgent(agent);
+            connectorAddress = vm.getAgentProperties().getProperty(CONNECTOR_ADDRESS);
+            assert connectorAddress != null;
+        }
+
+        // connect to agent
+        JMXServiceURL url = new JMXServiceURL(connectorAddress);
+        JMXConnector c = JMXConnectorFactory.connect(url);
+        MBeanServerConnection server = c.getMBeanServerConnection();
+
+        // get the list of pools
+        Set<ObjectName> mbeans = server.queryNames(
+            new ObjectName("java.nio:type=BufferPool,*"), null);
+        List<BufferPoolMXBean> pools = new ArrayList<BufferPoolMXBean>();
+        for (ObjectName name: mbeans) {
+            BufferPoolMXBean pool = ManagementFactory
+                .newPlatformMXBeanProxy(server, name.toString(), BufferPoolMXBean.class);
+            pools.add(pool);
+        }
+
+        // print headers
+        for (BufferPoolMXBean pool: pools)
+            System.out.format("         %8s             ", pool.getName());
+        System.out.println();
+        for (int i=0; i<pools.size(); i++)
+            System.out.format("%6s %10s %10s  ",  "Count", "Capacity", "Memory");
+        System.out.println();
+
+        // poll and print usage
+        for (;;) {
+            for (BufferPoolMXBean pool: pools) {
+                System.out.format("%6d %10d %10d  ",
+                    pool.getCount(), pool.getTotalCapacity(), pool.getMemoryUsed());
+            }
+            System.out.println();
+            Thread.sleep(2000);
+        }
+    }
+}