1
// 创建ByteBuffer
2
ByteBuffer buffer = ByteBuffer.allocate(1024); // 堆内缓冲区
3
ByteBuffer directBuffer = ByteBuffer.allocateDirect(1024); // 直接缓冲区（堆外）
4

5
// 写入数据
6
buffer.put((byte) 1);
7
buffer.put(new byte[]{2, 3, 4});
8

9
// 切换到读模式——这个最容易忘！
10
buffer.flip();
11

12
// 读取数据
13
byte b1 = buffer.get();
14
byte[] bytes = new byte[3];
15
buffer.get(bytes);
16

17
// 清空缓冲区，切回写模式
18
buffer.clear();
19

20
// 压缩缓冲区——保留未读的数据
21
buffer.compact();
22

23
// 标记和重置
24
buffer.mark();
25
// 读了一些数据...
26
buffer.reset(); // 回到标记位置

1
// FileChannel 读写示例
2
RandomAccessFile file = new RandomAccessFile("data.txt", "rw");
3
FileChannel fileChannel = file.getChannel();
4

5
ByteBuffer buffer = ByteBuffer.allocate(1024);
6

7
// 从文件读到缓冲区
8
int bytesRead = fileChannel.read(buffer);
9
while (bytesRead != -1) {
10
    buffer.flip();
11
    while (buffer.hasRemaining()) {
12
        System.out.print((char) buffer.get());
13
    }
14
    buffer.clear();
15
    bytesRead = fileChannel.read(buffer);
16
}
17

18
// 写入数据到文件
19
buffer.put("Hello, NIO!".getBytes());
20
buffer.flip();
21
fileChannel.write(buffer);
22

23
fileChannel.close();
24
file.close();

1
// 创建选择器
2
Selector selector = Selector.open();
3

4
// 打开ServerSocketChannel，设置为非阻塞
5
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
6
serverSocketChannel.bind(new InetSocketAddress(8080));
7
serverSocketChannel.configureBlocking(false);
8

9
// 注册到选择器，关注ACCEPT事件
10
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
11

12
while (true) {
13
    // 阻塞直到有事件发生
14
    int readyChannels = selector.select();
15
    if (readyChannels == 0) continue;
16

17
    Set<SelectionKey> selectionKeys = selector.selectedKeys();
18
    Iterator<SelectionKey> iterator = selectionKeys.iterator();
19

20
    while (iterator.hasNext()) {
21
        SelectionKey key = iterator.next();
22

23
        if (key.isAcceptable()) {
24
            // 新连接来了
25
            ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
26
            SocketChannel socketChannel = serverChannel.accept();
27
            socketChannel.configureBlocking(false);
28
            socketChannel.register(selector, SelectionKey.OP_READ);
29
        } else if (key.isReadable()) {
30
            // 有数据可读
31
            SocketChannel socketChannel = (SocketChannel) key.channel();
32
            ByteBuffer buffer = ByteBuffer.allocate(1024);
33
            int bytesRead = socketChannel.read(buffer);
34
            if (bytesRead == -1) {
35
                socketChannel.close();
36
                key.cancel();
37
            } else if (bytesRead > 0) {
38
                buffer.flip();
39
                byte[] data = new byte[buffer.remaining()];
40
                buffer.get(data);
41
                System.out.println("收到: " + new String(data));
42
            }
43
        }
44

45
        // 重要！要移除已处理的key
46
        iterator.remove();
47
    }
48
}

1
SocketChannel socketChannel = SocketChannel.open();
2
socketChannel.configureBlocking(false);
3

4
// 非阻塞连接
5
boolean connected = socketChannel.connect(new InetSocketAddress("localhost", 8080));
6
if (!connected) {
7
    while (!socketChannel.finishConnect()) {
8
        // 可以做其他事情
9
        System.out.println("连接中...");
10
    }
11
}
12

13
// 非阻塞读取
14
ByteBuffer buffer = ByteBuffer.allocate(1024);
15
int bytesRead = socketChannel.read(buffer);
16
// bytesRead可能是0（没数据）、-1（连接关闭）、>0（有数据）

1
ByteBuffer directBuffer = ByteBuffer.allocateDirect(1024);

1
FileChannel fileChannel = new RandomAccessFile("data.txt", "rw").getChannel();
2
MappedByteBuffer mappedBuffer = fileChannel.map(
3
    FileChannel.MapMode.READ_WRITE, 0, fileChannel.size());
4

5
// 直接修改内存中的数据
6
for (int i = 0; i < mappedBuffer.limit(); i++) {
7
    byte b = mappedBuffer.get(i);
8
    mappedBuffer.put(i, (byte) (b + 1));
9
}
10

11
fileChannel.close();

1
// 分散读取
2
ByteBuffer header = ByteBuffer.allocate(100);
3
ByteBuffer body = ByteBuffer.allocate(1024);
4
ByteBuffer[] buffers = {header, body};
5
socketChannel.read(buffers);
6

7
// 聚集写入
8
ByteBuffer headerBuf = ByteBuffer.wrap("HTTP/1.1 200 OK\r\n".getBytes());
9
ByteBuffer bodyBuf = ByteBuffer.wrap("Hello, World!\r\n".getBytes());
10
socketChannel.write(new ByteBuffer[]{headerBuf, bodyBuf});