Java NIO：读取可变大小的块

发布于 2024-08-02 13:01:21 字数 428 浏览 5 评论 0原文

我想从 TCP 流中读取一个字符串，该字符串给出字节长度，后跟实际数据。在Python中，我会做

length = ord(stream.read(1))
data = stream.read(length)

如何在Java NIO中做同样的事情？我拥有的是一个缓冲区（容量为 257）

stream.read(buffer); // cannot specify a size here
int length = buffer.get();
byte[] data = new byte[length];
buffer.get(data);

不幸的是，这不起作用： get() 调用读取过去缓冲区中的数据:-(

我可能需要翻转、倒带的某种组合，重置等等，但我无法弄清楚。

原文

I would like to read a string from a TCP stream that is given with a byte length followed by the actual data. In Python, I would do

length = ord(stream.read(1))
data = stream.read(length)

How do I do the same in Java NIO? What I have is a buffer (of capacity 257)

stream.read(buffer); // cannot specify a size here
int length = buffer.get();
byte[] data = new byte[length];
buffer.get(data);

Unfortunately, this doesn't work: the get() calls read past the data in the buffer :-(

I probably need some combination of flip, rewind, reset, etc., but I can't figure it out.

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野稚 2024-08-09 13:01:21

如果 stream 是 SocketChannel 并且 buffer 是 ByteBuffer，您可以执行以下操作：

//assuming buffer is a ByteBuffer
buffer.position(0);
buffer.limit(1);
while (buffer.hasRemaining()) { 
   stream.read(buffer);
}
buffer.rewind();

//get the byte and cast it into the range 0-255
int length = buffer.get() & 0xFF;
buffer.clear();
buffer.limit(length);
while (buffer.hasRemaining()) { 
   stream.read(buffer);
}
buffer.rewind();
//the buffer is now ready for reading the data from

if stream is a SocketChannel and buffer is a ByteBuffer, you can do the following:

//assuming buffer is a ByteBuffer
buffer.position(0);
buffer.limit(1);
while (buffer.hasRemaining()) { 
   stream.read(buffer);
}
buffer.rewind();

//get the byte and cast it into the range 0-255
int length = buffer.get() & 0xFF;
buffer.clear();
buffer.limit(length);
while (buffer.hasRemaining()) { 
   stream.read(buffer);
}
buffer.rewind();
//the buffer is now ready for reading the data from

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