ByteBuf
	提供了读索引和写索引来控制字节数组

	1.维护了readerIndex和writerIndex
	2.readerIndex大于writerIndex时会抛出越界异常
	3.ByteBuf容量=writerIndex
	4.ByteBuf可读容量=writerIndex-readerIndex
	5.readXXX()和writeXXX()方法将会推进其对应的索引
	6.getXXX()和setXXX()方法将对两个索引无影响

	使用模式分为:
		1.HeapBuffer
		2.DirectBuffer
		3.CompositeBuffer
	HeapBuffer:
		public static void heapBuffer() {
		    // 创建Java堆缓冲区
		    ByteBuf heapBuf = Unpooled.buffer(); 
		    if (heapBuf.hasArray()) { // 是数组支撑
		        byte[] array = heapBuf.array();
		        int offset = heapBuf.arrayOffset() + heapBuf.readerIndex();
		        int length = heapBuf.readableBytes();
		        handleArray(array, offset, length);
		    }
		}
	DirectBuffer:
		public static void directBuffer() {
		    ByteBuf directBuf = Unpooled.directBuffer();
		    if (!directBuf.hasArray()) {
		        int length = directBuf.readableBytes();
		        byte[] array = new byte[length];
		        directBuf.getBytes(directBuf.readerIndex(), array);
		        handleArray(array, 0, length);
		    }
		}
	CompositeBuffer:
		本质上类似于提供一个或多个ByteBuf的组合视图，可以根据需要添加和删除不同类型的ByteBuf
		public static void byteBufComposite() {
		    // 复合缓冲区，只是提供一个视图
		    CompositeByteBuf messageBuf = Unpooled.compositeBuffer();
		    ByteBuf headerBuf = Unpooled.buffer(); // can be backing or direct
		    ByteBuf bodyBuf = Unpooled.directBuffer();   // can be backing or direct
		    messageBuf.addComponents(headerBuf, bodyBuf);
		    messageBuf.removeComponent(0); // remove the header
		    for (ByteBuf buf : messageBuf) {
		        System.out.println(buf.toString());
		    }
		}