Java の Object のサイズを簡単に測定する

コード

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;

public class ObjectUtils {
    public static int getObjectSize(Object o) {
        ObjectOutput out = null;
        try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
            out = new ObjectOutputStream(bos);
            out.writeObject(o);
            out.flush();
            byte[] b = bos.toByteArray();
            return b.length;
        } catch (IOException e) {
            return -1;
        }
    }
}

使い方

    public static void main(String[] args) {
        {
            String o = "ABC";
            System.err.println(ObjectUtils.getObjectSize(o));
        }
        {
            Integer o = 100;
            System.err.println(ObjectUtils.getObjectSize(o));
        }
        {
            String[] o = { "ABC", "ABC", "ABC" };
            System.err.println(ObjectUtils.getObjectSize(o));
        }
    }

実行結果例

10
81
60