查看java对象所占内存大小的方法

System.setProperty("java.vm.name","Java HotSpot(TM) ");
System.out.println(ObjectSizeCalculator.getObjectSize(3L));

        <dependency>
            <groupId>org.apache.lucene</groupId>
            <artifactId>lucene-core</artifactId>
            <version>4.0.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.12.0</version>
        </dependency>

        Map<String, String> map = new HashMap<>();
        System.out.println("map init value is " + RamUsageEstimator.sizeOf(map));
        for (int i = 0; i < 100; i++) {
            RandomStringUtils.randomAlphanumeric(100);
            map.put(RandomStringUtils.randomAlphanumeric(10), RandomStringUtils.randomAlphanumeric(10));
        }
        System.out.println("map size 100, value is " + RamUsageEstimator.sizeOf(map));
        System.out.println("map size 100, value is " + RamUsageEstimator.humanSizeOf(map));

        <dependency>
            <groupId>org.openjdk.jol</groupId>
            <artifactId>jol-core</artifactId>
            <version>0.9</version>
        </dependency>

System.out.println(ClassLayout.parseInstance(23L).toPrintable());