2、计算Java对象所占内存的大小

当一个对象有多个属性，需要计算整个对象的大小时，可以借助org.apache.lucene工具类
首先引入maven依赖

<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>

测试代码

public void test() {
    List<User> userList = new ArrayList<>();
    User xh = new User();
    xh.setName("xiaohong");
    xh.setAge(2);
    for (int i = 0; i < 1000; i++) {
        userList.add(xh);
    }
    System.out.println("value is:" + RamUsageEstimator.humanSizeOf(userList));
}
@Data
class User {
    private String name;
    private int age;
}

执行结果展示

value is:4.9 KB