有没有办法只用Java在指针中创建一个直接的ByteBuffer？

问题描述

或者我必须有一个调用env-> NewDirectByteBuffer（缓冲区，大小）的JNI辅助函数？

解决方案

我所做的是创建一个普通的DirectByteBuffer并更改它的地址。

 字段地址= Buffer.class.getDeclaredField（address） ; 
 address.setAccessible（true）; 
字段容量= Buffer.class.getDeclaredField（capacity）; 
 capacity.setAccessible（true）; 
 
 ByteBuffer bb = ByteBuffer.allocateDirect（0）.order（ByteOrder.nativeOrder（））; 
 address.setLong（bb，addressYouWantToSet）; 
 capacity.setInt（bb，theSizeOf）; 
  

从这一点开始，您可以访问引用基础地址的ByteBuffer。我这样做是为了访问网络适配器上的内存零拷贝而且工作正常。

你可以直接为你的地址创建一个DirectByteBuffer，但这更加模糊。 / p>

---

另一种方法是使用Unsafe（这仅适用于OpenJDK / HotSpot JVM和本机字节顺序）

  Unsafe.getByte（address）; 
 Unsafe.getShort（address）; 
 Unsafe.getInt（address）; 
 Unsafe.getLong（地址）; 
  

Or do I have to have a JNI helper function that calls env->NewDirectByteBuffer(buffer, size)?

解决方案

What I do is create a normal DirectByteBuffer and change it's address.

Field address = Buffer.class.getDeclaredField("address");
address.setAccessible(true);
Field capacity = Buffer.class.getDeclaredField("capacity");
capacity.setAccessible(true);

ByteBuffer bb = ByteBuffer.allocateDirect(0).order(ByteOrder.nativeOrder());
address.setLong(bb, addressYouWantToSet);
capacity.setInt(bb, theSizeOf);

From this point you can access the ByteBuffer referencing the underlying address. I have done this for accessing memory on network adapters for zero copy and it worked fine.

You can create the a DirectByteBuffer for your address directly but this is more obscure.

---

An alternative is to use Unsafe (this only works on OpenJDK/HotSpot JVMs and in native byte order)

Unsafe.getByte(address);
Unsafe.getShort(address);
Unsafe.getInt(address);
Unsafe.getLong(address);

这篇关于有没有办法只用Java在指针中创建一个直接的ByteBuffer？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！