Creates a newly allocated byte array. Its size is the current size of this output stream and the valid contents of the buffer have been copied into it.
Creates a newly allocated byte array. Its size is the current size of this output stream and the valid contents of the buffer have been copied into it.
新创建一个过渡性的瞬态的字节数组，这个数组的大小是输入流在缓冲中当前的大小，内容是输入流在缓冲中当前的内容，这个方法执行后，当前输入流的缓冲被重置。