mark 是在读取时，做一个标记，即使 position 改变，只要调用 reset 就能回到 mark 的位置
注意
rewind 和 flip 都会清除 mark 位置
字符串与 ByteBuffer 互转
ByteBuffer buffer1 = StandardCharsets.UTF_8.encode("你好"); ByteBuffer buffer2 = Charset.forName("utf-8").encode("你好");
debug(buffer1); debug(buffer2);
CharBuffer buffer3 = StandardCharsets.UTF_8.decode(buffer1); System.out.println(buffer3.getClass()); System.out.println(buffer3.toString());
结果 +-------------------------------------------------+ | 0 1 2 3 4 5 6 7 8 9 a b c d e f | +--------+-------------------------------------------------+----------------+ |00000000| e4 bd a0 e5 a5 bd |...... | +--------+-------------------------------------------------+----------------+ +-------------------------------------------------+ | 0 1 2 3 4 5 6 7 8 9 a b c d e f | +--------+-------------------------------------------------+----------------+ |00000000| e4 bd a0 e5 a5 bd |...... | +--------+-------------------------------------------------+----------------+ class java.nio.HeapCharBuffer 你好
