java 查看对象占用内存大小（代码库）

<dependency>
    <groupId>com.carrotsearch</groupId>
    <artifactId>java-sizeof</artifactId>
    <version>0.0.5</version>
</dependency>

import com.carrotsearch.sizeof.RamUsageEstimator;
import com.google.common.cache.Cache;

import java.util.UUID;

public class Test3 {
    // 10 秒钟过期
    private static Cache<String, Integer> guavaCache = CacheFactory.cached(10L, null);

    public static void main(String[] args) {
        for (int i = 0; i < 100000; i++) {
            String id = UUID.randomUUID().toString();
            guavaCache.put(id, i);
        }
        long size = RamUsageEstimator.sizeOf(guavaCache);
        System.out.println(size + " b");
        long kb = size / 1024;
        System.out.println(kb + " kb");
        long m = kb / 1024;
        System.out.println(m + " m");
    }
}

输出
20249888 b
19775 kb
19 m

10W数据，占19M