如何在Android中获取对象大小

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[TODO] 如何在Android中获取对象大小。

如何在Java中获取对象大小

instrumentation

一种方式是使用instrumentation，该方法在Calculate size of Object in Java和In Java, what is the best way to determine the size of an object?中均有介绍

但这种方式最终需要以如下较为繁琐的方式调用：

java -javaagent:ObjectSizeFetcherAgent.jar C

其中jar包包含检查对象大小的代码，而C是待测试的对象。

ObjectGraphMeasurer

https://github.com/DimitrisAndreou/memory-measurer

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import objectexplorer.ObjectGraphMeasurer;

public class Measurer {

  public static void main(String[] args) {
    Set<Integer> hashset = new HashSet<Integer>();
    Random random = new Random();
    int n = 10000;
    for (int i = 1; i <= n; i++) {
      hashset.add(random.nextInt());
    }
    System.out.println(ObjectGraphMeasurer.measure(hashset));
  }
}

ObjectSizeCalculator

jdk.nashorn.internal.ir.debug.ObjectSizeCalculator

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System.out.println(ObjectSizeCalculator.getObjectSize(new gnu.trove.map.hash.TObjectIntHashMap<String>(12000, 0.6f, -1)));
System.out.println(ObjectSizeCalculator.getObjectSize(new HashMap<String, Integer>(100000)));
System.out.println(ObjectSizeCalculator.getObjectSize(3));
System.out.println(ObjectSizeCalculator.getObjectSize(new int[]{1, 2, 3, 4, 5, 6, 7 }));
System.out.println(ObjectSizeCalculator.getObjectSize(new int[100]));

164192
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416

其他方式

jol

jol

sizeof

sizeof

an article on determining the size of composite and potentially nested Java objects

ObjectSizer

ObjectSizer

序列化

序列化(但有些人不推荐这种做法)

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Serializable ser;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(ser);
oos.close();
return baos.size();

如何在Android中获取对象大小

貌似没有好的解决办法。但是LeakCanary中可以输出类似日志。它是如何获取对象大小的呢？

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In com.sunmoonblog.memperf:1.0:1.
            * com.sunmoonblog.memperf.Box has leaked:
            * GC ROOT static com.sunmoonblog.memperf.Docker.container
            * leaks com.sunmoonblog.memperf.Box instance
            
            * Retaining: 20 B.
            * Reference Key: 04d239b5-2409-48f5-bc54-2432d6eabe61
            * Device: Genymotion Android Google Nexus 5X - 7.0.0 - API 24 - 1080x1920 vbox86p
            * Android Version: 7.0 API: 24 LeakCanary: 1.5.4 74837f0
            * Durations: watch=5001ms, gc=104ms, heap dump=5136ms, analysis=19166ms

方案二

来源

建议翻一下Dalvik VM源码。对象的大小存储在 ClassObject::objectSize : size_t, 源码见 dalvik/vm/oo/Object.h

建议从 dalvik/vm/alloc/Alloc.cpp 的 dvmTrackAllocation()开始看起。 new操作符会调用到这个方法。