NIO 伺服器和客戶端 demo 如下：

public class TestNonBlockingNIO {

    //客戶端
    @Test
    public void client() throws IOException{
        // 1. 獲取通道
        SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 9898));
        // 2. 切換非阻塞模式
        sChannel.configureBlocking(false);
        
 
// 3. 分配指定大小的緩衝區
        ByteBuffer buf = ByteBuffer.allocate(1024);
        // 4. 傳送資料給服務端
        String str = "hello";
        buf.put((new Date().toString() + "\n" + str).getBytes());
        buf.flip();
        sChannel.write(buf);
        sChannel.shutdownOutput();
        // 5. 關閉通道
        sChannel.close();
    }

    
 
//服務端
    @Test
    public void server() throws IOException{
        //1. 獲取通道
        ServerSocketChannel ssChannel = ServerSocketChannel.open();
        //2. 切換非阻塞模式
        ssChannel.configureBlocking(false);
        //3. 繫結連線
        ssChannel.bind(new InetSocketAddress(9898));
        //4. 獲取選擇器
        Selector selector = Selector.open();
        
 
//5. 將通道註冊到選擇器上, 並且指定“監聽接收事件”
        ssChannel.register(selector, SelectionKey.OP_ACCEPT);
        //6. 輪詢式的獲取選擇器上已經“準備就緒”的事件
        while(selector.select() > 0){
            //7. 獲取當前選擇器中所有註冊的“選擇鍵(已就緒的監聽事件)”
            Iterator<SelectionKey> it = selector.selectedKeys().iterator();
            while(it.hasNext()){
                //8. 獲取準備“就緒”的是事件
                SelectionKey sk = it.next();
                //9. 判斷具體是什麼事件準備就緒
                if(sk.isAcceptable()){
                    ServerSocketChannel ss = (ServerSocketChannel) sk.channel();
                    //10. 若“接收就緒”，獲取客戶端連線
                    SocketChannel sChannel = ss.accept();
                    //11. 切換非阻塞模式
                    sChannel.configureBlocking(false);
                    //12. 將該通道註冊到選擇器上
                    sChannel.register(selector, SelectionKey.OP_READ);
                }else if(sk.isReadable()){
                    //13. 獲取當前選擇器上“讀就緒”狀態的通道
                    SocketChannel sChannel = (SocketChannel) sk.channel();
                    //14. 讀取資料
                    ByteBuffer buf = ByteBuffer.allocate(1024);
                    int len = 0;
                    while((len = sChannel.read(buf)) > 0 ){
                        buf.flip();
                        System.out.println(new String(buf.array(), 0, len));
                        buf.clear();
                    }
                    if(len == -1){
                        System.out.println("斷開");
                        sChannel.close();
                    }
                }
                //15. 取消選擇鍵 SelectionKey
                it.remove();
            }
        }
    }
}

轉自：https://www.cnblogs.com/vegeta-xiao/p/12612561.html