Spring Boot Memory Leak Debugging — Practical Guide

Memory leaks are one of the most dangerous production problems.
The application works fine at startup… then slowly becomes slow, CPU spikes, and finally crashes.

In Spring Boot applications, leaks usually come from object retention — not from missing free() like in C/C++.

This guide shows how to detect, analyze, and fix memory leaks in real production systems.

📌 Symptoms of Memory Leak

Typical production signs:

  • RAM usage keeps increasing

  • GC runs continuously

  • CPU usage rises

  • Application restarts automatically

  • Eventually OutOfMemoryError

🖼️ Memory Leak Behavior Over Time

Step 1️⃣ Confirm the Leak

Check memory usage inside JVM.

jstat -gc <pid> 1000

If heap never drops after GC → leak confirmed.

Step 2️⃣ Capture Heap Dump

jmap -dump:live,format=b,file=heap.hprof <pid>

This file contains all objects currently in memory.

Step 3️⃣ Analyze Heap Dump

Open using:

  • Eclipse MAT

  • VisualVM

🖼️ Heap Dump Analysis

Look for:

Largest retained objects
That’s usually the leak.

Common Spring Boot Leak Causes

1️⃣ Static Collections

static List<User> cache = new ArrayList<>();

Objects never removed → heap grows forever.

2️⃣ Unbounded Cache

Map<Long, Order> orders = new HashMap<>();

Fix → use size limit or expiry.

3️⃣ ThreadLocal Not Cleared

ThreadLocal<User> userContext = new ThreadLocal<>();

Always call:

userContext.remove();

4️⃣ Entity Graph Loading

Returning full entities loads huge object graphs.

Fix → DTOs.

5️⃣ Listener / Scheduler Objects

Objects stored in scheduled tasks remain forever.

🖼️ Retained Objects Example

Step 4️⃣ Fix & Verify

After fixing:

Monitor heap again.

Memory should stabilize after GC cycles.

Prevent Memory Leaks

✔ Limit caches
✔ Close streams
✔ Avoid static collections
✔ Monitor heap
✔ Use weak references when needed

Useful JVM Options

-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/logs

Automatically capture dump in production.

📚 Recommended Reading

🎯 Conclusion

Memory leaks are not random failures.

They are retained references.

Once you learn heap analysis, debugging becomes systematic instead of guessing.

💼 Professional Support Available

If you are facing issues in real projects related to enterprise backend development or workflow automation, I provide paid consulting, production debugging, project support, and focused trainings.

Technologies covered include Java, Spring Boot, PL/SQL, CMS, Azure, and workflow automation (jBPM, Camunda BPM, RHPAM).


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