Android-那些年我们进过的坑-ByteBuffer导致的bug

Android-那些年我们进过的坑-ByteBuffer导致的bug

前几天发现这么一个问题，自己实现的序列化，按字节操作。5.0一直没测试，发现反序列化有问题，一直以为数据库的问题。折腾了一晚上。

都知道在5.0 google做了好多优化。

我们使用了allocateDirect,debug发现5.0上出问题的时候offset不是0，而5.0一下的时候offset都是0

4.4中的源码

DirectByteBuffer第三个参数是offset，5.0一下是写死的

/**
* Creates a direct byte buffer based on a newly allocated memory block.
*
* @param capacity
*            the capacity of the new buffer
* @return the created byte buffer.
* @throws IllegalArgumentException
*             if {@code capacity < 0}.
*/
public static ByteBuffer allocateDirect(int capacity) {
if (capacity < 0) {
throw new IllegalArgumentException("capacity < 0: " + capacity);
}
return new DirectByteBuffer(MemoryBlock.allocate(capacity), capacity, 0, false, null);
}

5.0的源码这样子

/**
* Creates a direct byte buffer based on a newly allocated memory block.
*
* @param capacity
*            the capacity of the new buffer
* @return the created byte buffer.
* @throws IllegalArgumentException
*             if {@code capacity < 0}.
*/
public static ByteBuffer allocateDirect(int capacity) {
if (capacity < 0) {
throw new IllegalArgumentException("capacity < 0: " + capacity);
}
// Ensure alignment by 8.
MemoryBlock memoryBlock = MemoryBlock.allocate(capacity + 7);
long address = memoryBlock.toLong();
long alignedAddress = (address + 7) & ~(long)7;
return new DirectByteBuffer(memoryBlock, capacity, (int)(alignedAddress - address), false, null);
}

在5.0后 做了内存对齐alignedAddress - address，直接读取的字节array还是从地址最开始，导致读取了一堆0.反序列化就出问题了。