How to Capture Java Heap Dumps Efficiently with jmap, jcmd, and JVisualVM

Heap dumps are essential for diagnosing memory leaks, garbage‑collection problems, java.lang.OutOfMemoryError, and for optimizing memory consumption.

jmap

jmap is bundled with the JDK and can write a heap dump to a specified file.

jmap -dump:format=b,file=<file-path> <pid>
# pid: Java process ID
# file-path: destination file for the dump

Example:

jmap -dump:format=b,file=/opt/tmp/heapdump.bin 37320

Use the live option to include only live objects and keep the dump size manageable.

HeapDumpOnOutOfMemoryError

Setting the JVM flag -XX:+HeapDumpOnOutOfMemoryError makes the JVM automatically generate a heap dump when an OOM occurs.

Specify the output location with -XX:HeapDumpPath.

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/opt/tmp/heapdump.bin

Best practice: enable this flag in all applications to ensure a dump is captured at the moment of failure.

jcmd

jcmd, also part of the JDK, sends diagnostic commands to a running JVM.

jcmd <pid> GC.heap_dump <file-path>
# pid: Java process ID
# file-path: destination file for the dump

Example:

jcmd 37320 GC.heap_dump /opt/tmp/heapdump.bin

JVisualVM

JVisualVM is a graphical monitoring and troubleshooting tool bundled with the JDK.

Launch jvisualvm from the JDK bin directory.

Right‑click a Java process and choose “Heap Dump”.

The dump is written to the file path shown under the “Summary → Basic Info → File” tab.

JMX (HotSpotDiagnostic MBean)

The MBean com.sun.management:type=HotSpotDiagnostic provides a dumpHeap operation. outputFile: path for the heap dump. live: set to true to capture only live objects.

Clients such as JConsole, jmxsh, or Java Mission Control can invoke this operation. Example using JConsole is shown below.

Programmatic Capture

Applications can trigger a heap dump programmatically by calling the same HotSpotDiagnostic MBean via JMX.

// Example Java code to invoke dumpHeap
HotSpotDiagnosticMXBean mxBean = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class);
mxBean.dumpHeap("/opt/tmp/heapdump.bin", true); // true = live objects only