NIO
java IO 的核心是流Stream。
输入流和输出流
字节流和字符流
读数据的逻辑：
- open a stream
- while more information
- read information
- close the stream
写数据的逻辑：
- open a stream
- while more information
- write information
- close the stream
节点流和过滤流
Decorator设计模式
InputStream
FilterInputStream
BufferedInputStream
A container for data of a specific primitive type.
A buffer is a linear, finite sequence of elements of a specific primitive type. Aside from its content, the essential properties of a buffer are its capacity, limit, and position
A buffer's limit is the index of the first element that should not be read or written.
