JOL JAVA对象布局

JOL = Java Object Layout 分析对象在JVM的大小和分布

官网：http://openjdk.java.net/projects/code-tools/jol/

pom依赖
<dependencies>
    <!-- https://mvnrepository.com/artifact/org.openjdk.jol/jol-core -->
    <dependency>
        <groupId>org.openjdk.jol</groupId>
        <artifactId>jol-core</artifactId>
        <version>0.9</version>
    </dependency>
</dependencies>

上代码：

public class Test {
    static Object getObject() {
        Map<String, Object> map = new HashMap<>();
        map.put("a", 1L);
        map.put("b", "b");
        map.put("c", new Date());
        for (int i = 0; i < 10; i++) {
            map.put(String.valueOf(i), String.valueOf(i));
        }
        return map;
    }

    public static void main(String[] args) {
        Object obj = getObject();
        //查看对象内部信息
        System.out.println(ClassLayout.parseInstance(obj).toPrintable());
        System.out.println("----------我是分割线---------------");
        //查看对象外部信息
        System.out.println(GraphLayout.parseInstance(obj).toPrintable());
        System.out.println("----------我是分割线---------------");
        //获取对象总大小
        System.out.println("size : " + GraphLayout.parseInstance(obj).totalSize());
    }
}