Java Object Size

Determining Java Object Size: Several approaches exist, each with trade-offs. For simple objects, Instrumentation offers precision but requires JVM agent attachment. For broader estimates, consider these:

1. Shallow Size (Instrumentation): This measures the object's header and its direct fields' sizes.

import java.lang.instrument.Instrumentation;

public class ObjectSize {
    private static Instrumentation instrumentation;

    public static void premain(String args, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object obj) {
        return instrumentation.getObjectSize(obj);
    }

    public static void main(String[] args) {
        // Requires agent attachment (e.g., -javaagent:path/to/agent.jar)
        MyObject myObj = new MyObject();
        System.out.println("Size: " + getObjectSize(myObj));
    }

    static class MyObject {
        int x;
        String s;
    }
}

2. Deep Size (Approximation): This accounts for referenced objects' sizes, recursively. No standard library provides this; consider a third-party library or manual calculation (highly complex and error-prone for large graphs).

3. Libraries: Libraries like SizeOf offer deep size estimation.

Spring Boot Considerations: Spring Boot doesn't directly impact object size calculation; the methods above apply equally.

Choosing the right method: Use Instrumentation for accurate shallow size. Deep size requires careful consideration; approximations may suffice for many use cases. Remember that heap fragmentation and JVM implementation can influence actual memory usage.