package com.ethjava;

import sun.misc.Unsafe;

import java.lang.reflect.Field;

import java.lang.reflect.Modifier;

import java.util.HashSet;

public class ClearMemory {

public static Unsafe UNSAFE = null;

public static void main(String[] args) {

String password = new String("11111111");

String fake = new String(password.replaceAll(".", "?"));

System.out.println(password); // l00k@myHor$e

System.out.println(fake); // ????????????

getUnsafe().copyMemory(fake, 0L, null, toAddress(password), sizeOf(password));

// getUnsafe().copyMemory(fake, 0L, null, toAddress(password), password.getBytes().length);

System.out.println(password); // ????????????

System.out.println(fake); // ????????????

}

public static Unsafe getUnsafe() {

if (UNSAFE != null) return UNSAFE;

try {

Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");

theUnsafe.setAccessible(true);

UNSAFE = (Unsafe) theUnsafe.get(null);

System.out.println(UNSAFE);

} catch (NoSuchFieldException | IllegalAccessException e) {

e.printStackTrace();

}

return UNSAFE;

}

public static long toAddress(Object obj) {

Object[] array = new Object[]{obj};

long baseOffset = getUnsafe().arrayBaseOffset(Object[].class);

return normalize(getUnsafe().getInt(array, baseOffset));

}

public static Object fromAddress(long address) {

Object[] array = new Object[]{null};

long baseOffset = getUnsafe().arrayBaseOffset(Object[].class);

getUnsafe().putLong(array, baseOffset, address);

return array[0];

}

public static long normalize(int value) {

if (value >= 0) return value;

return (~0L >>> 32) & value;

}

public static long sizeOf(Object o) {

Unsafe u = getUnsafe();

HashSet<Field> fields = new HashSet<Field>();

Class c = o.getClass();

while (c != Object.class) {

for (Field f : c.getDeclaredFields()) {

if ((f.getModifiers() & Modifier.STATIC) == 0) {

fields.add(f);

}

}

c = c.getSuperclass();

}

// 获得偏移

long maxSize = 0;

for (Field f : fields) {

long offset = u.objectFieldOffset(f);

if (offset > maxSize) {

maxSize = offset;

}

}

return ((maxSize / 8) + 1) * 8; // padding

}

}