简介：我有一个ByteBuffer,我在其中提取一些数据.之后,我想通过Socket发送这些数据.

所以,我写了这样的代码：

    private static void serialize(ByteBuffer buffer, EmployeeData emp, CharsetEncoder encoder)
{
    // id
    buffer.putInt(emp.getId());

    CharBuffer nameBuffer = CharBuffer.wrap(emp.getFirstName().toCharArray());
    ByteBuffer nbBuffer = null;

    // length of first name
    try
    {
        nbBuffer = encoder.encode(nameBuffer);
    } 
    catch(CharacterCodingException e)
    {
        throw new ArithmeticException();
    }

    System.out.println(String.format("String [%1$s] #bytes = %2$s", emp.getFirstName(), nbBuffer.limit()));
    buffer.putInt(nbBuffer.limit());
    buffer.put(nbBuffer);

    // put lastname
    nameBuffer = CharBuffer.wrap(emp.getLastName().toCharArray());
    nbBuffer = null;

    // length of first name
    try
    {
        nbBuffer = encoder.encode(nameBuffer);          
    } 
    catch(CharacterCodingException e)
    {
        throw new ArithmeticException();
    }

    System.out.println(String.format("String [%1$s] #bytes = %2$s", emp.getLastName(), nbBuffer.limit()));
    buffer.putInt(nbBuffer.limit());
    buffer.put(nbBuffer);

    // salary
    buffer.putInt(emp.getSalary());
}

在调用代码中,我执行以下操作.我首先得到序列化的ByteBuffer,然后将其写入套接字……

            Socket client = new Socket("localhost", 8080);

        OutputStream oStream = client.getOutputStream();

        serialize(buffer, emp, encoder);

        buffer.rewind();            
        while(buffer.hasRemaining())
        {
            byte temp = buffer.get();
            ++ written;
        }

        buffer.rewind();
        System.out.println("#Bytes in output buffer: " + written + " limit = " + buffer.limit() + " pos = " + buffer.position() + " remaining = " + buffer.remaining());

        int remaining = buffer.remaining();
        while(remaining > 0)
        {
            oStream.write(buffer.get());
            -- remaining;
        }

我期望buffer.remaining()应该完全等于我输入缓冲区的#bytes.但是我发现它不是,它总是等于1024,这是缓冲区底层数组的大小.

这就是我创建缓冲区的方法……

        Charset charset = Charset.forName("UTF-8");
    CharsetDecoder decoder = charset.newDecoder();
    CharsetEncoder encoder = charset.newEncoder();
    byte [] underlyingBuffer = new byte[1024];
    ByteBuffer buffer = ByteBuffer.wrap(underlyingBuffer);
    buffer.order(ByteOrder.LITTLE_ENDIAN);

这就是我得到的print语句输出…

String [John] #bytes = 4 String [Smith] #bytes = 5

#Bytes in output buffer: 1024 limit = 1024 pos = 0 remaining = 1024

如何获得放入缓冲区的确切#bytes？

谢谢！

解决方法:

当你完成将字节放入缓冲区时,你应该flip它.您可以这样做,而不是第一次回拨.

java.nio.Buffer区分容量和限制.如果不翻转它,则limit和capacity与初始化它的数组的长度相同.

通过翻转它,限制将设置为您编码的数据的末尾,容量仍然是1024. ByteBuffer#remaining查看位置和限制之间的差值.