Java ByteBuffer - 在 put 调用链中相对重新定位？

Question

这就是我想要做的，除了它有两个问题:position() 执行绝对定位，而不是相对定位(因此 -1 的参数是非法的)，并且您显然无法链接另一个方法调用在调用position()之后 - 编译器提示它无法识别putShort()。

// Method to create a packet header for sending a packet. The placement of the two numbers is
//  done according to little-endian encoding.
private byte[] createPacketHeader(EPacketType packetType, int fourBits,
                                  int totalMessageLength, int segmentSize) {

    return ByteBuffer.allocate(CPacketHeaderSize).order(ByteOrder.LITTLE_ENDIAN).
            put((byte) ((byte) (packetType.getValue() << 4) | (byte) fourBits)).
            putInt(totalMessageLength).  // Bottom 3 bytes of total length (+ 1 byte discarded)
            position(-1).  // Reposition to discard last byte from above call !!DOESN'T WORK!!
            putShort((short) segmentSize).  // Segment length
            put(_connectIdUtf8).  // Connection ID in UTF-8, should be <= 10 bytes
            array();  // This assumes zero initialization so final bytes are zero
}

这就是我目前正在做的事情。它确实有效，但与我希望我能做的相比似乎相当不优雅。

    ByteBuffer byteBuffer =
                     ByteBuffer.allocate(CPacketHeaderSize).order(ByteOrder.LITTLE_ENDIAN);

    byteBuffer.put((byte) ((byte) (packetType.getValue() << 4) | (byte) fourBits)).
            putInt(totalMessageLength).  // Bottom 3 bytes of total length (+ 1 byte discarded)
            position(byteBuffer.position() -1);  // Discard last byte from above call

    byteBuffer.putShort((short) segmentSize).  // Segment length
            put(_connectIdUtf8);  // Connection ID in UTF-8, should be <= 10 bytes

    return byteBuffer.array();  // This assumes zero initialization so final bytes are zero

关于如何回到更接近第一次尝试的事情，有什么建议吗？

编辑: 感谢您的回答，他们都很有帮助。如果有人好奇，这就是我最终所做的:

// Method to create a packet header for sending a packet. The placement of the two numbers is
//  done according to little-endian encoding.
private byte[] createPacketHeader(EPacketType packetType, int fourBits,
                                  int totalMessageLength, int segmentSize) {

    return ByteBuffer.allocate(CPacketHeaderSize).order(ByteOrder.LITTLE_ENDIAN).
            put((byte) ((byte) (packetType.getValue() << 4) | (byte) fourBits)).
            put(intToThreeBytes(totalMessageLength)).  // Bottom 3 bytes of total length
            putShort((short) segmentSize).  // Segment length
            put(_connectIdUtf8).  // Connection ID in UTF-8, should be <= 10 bytes
            array();  // This assumes zero initialization so final bytes are zero
}


// Method to convert an int into a three-byte byte array, using little-endian encoding
private byte[] intToThreeBytes(int aNumber) {
    byte[] byteArray = new byte[3];
    for (int i = 0; i < 3; i++)
        byteArray[i] = (byte)(aNumber >> i * 8);
    return byteArray;
}

Answer 1

也缺少优雅:

byte[] bytes = ByteBuffer.allocate(4).putInt(totalMessageLength).array();
byteBuffer.put(bytes, 0, 3);