How Can JHat Help Me Find and Fix Java Memory Leaks?

Understanding Java Memory Leaks Using JHat

Finding memory leaks in Java can be a daunting task. However, by leveraging specialized tools such as JHat, you can effectively identify and resolve these issues.

One common approach is to analyze heap dumps taken from the JVM. After loading the heap dump into JHat, look for objects that have large sizes or are referenced by many other objects. To identify potential memory leaks, you can:

• Search for Large Objects: Use the "Objects" tab in JHat to sort objects by size. This allows you to identify objects that may be responsible for significant memory consumption.
• Identify Potential Roots: Examine the "Retained" tab to determine the references that are keeping objects alive. This can help you understand the source of the memory leak and identify the root cause.

In the case where large maps are suspected to cause the leak, you can apply the following technique:

1. Start the application and let it reach a stable state.
2. Perform the operation that triggers memory usage, repeating it several times to ensure initialization is complete.
3. Run GC and take a memory snapshot using JHat.
4. Repeat steps 2-3, taking a second memory snapshot.
5. Run a diff between the two snapshots and analyze the differences in object types.

This approach allows you to pinpoint the specific objects that are causing the memory leak, based on the increased object count between snapshots.

While paid tools like JProfiler offer advanced features, JHat, which is included with the JDK, provides a valuable resource for identifying Java memory leaks. By understanding the concepts of heap dumps and object references, you can effectively troubleshoot and resolve memory issues in your applications.

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