• 沒有統一的文件屬性（例如讀寫權限）；
• API能力比較弱，例如目錄的級聯創建和遞歸遍歷，往往需要自己實現；
• 底層存儲系統的一些高級API無法使用；
• 所有的文件操作都是同步阻塞調用，不支持異步文件讀寫操作。

• 提供能夠批量獲取文件屬性的API，這些API具有平臺無關性，不與特性的文件系統相耦合。另外它還提供了標準文件系統的SPI，供各個服務提供商擴展實現；
• 提供AIO功能，支持基于文件的異步i/O操作和針對網絡套接字的異步操作；

public class TimerServer {
    public static void main(String[] args) throws IOException {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
                //采用默認值
            }
        }
        ServerSocket server = null;
        try{
            server = new ServerSocket(port);
            System.out.println("The time server is start in port:" + port);
            Socket socket = null;
            while (true) {
                socket = server.accept();
                new Thread(new TimeServerHandler(socket)).start();
            }
        }finally {
            if (server != null) {
                System.out.println("The time server close");
                server.close();
                server = null;
            }
        }
    }
}

public class TimeServerHandler implements Runnable {

    private Socket socket;

    public TimeServerHandler() {

    }

    public TimeServerHandler(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        BufferedReader in = null;
        PrintWriter out = null;
        try {
            in = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
            out = new PrintWriter(this.socket.getOutputStream(), true);
            String currentTime = null;
            String body = null;
            while (true) {
                body = in.readLine();
                if (body == null) {
                    break;
                }
                System.out.println("The time server receive order:" + body);
                currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
                out.println(currentTime);
            }
        } catch (Exception e) {
            
        }finally{
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
            }
            if (out != null) {
                out.close();
                out = null;
            }
            if (this.socket != null) {
                try {
                    this.socket.close();
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
                this.socket = null;
            }
        }
    }
}

第37行通過BufferedReader讀取一行，如果已經讀到了輸入流的尾部，則返回值為null，推出循環。如果讀到了非空值，則對內容進行判斷，如果請求消息為查詢時間的指令

“QUERY TIME ORDER”，則獲取當前最新的系統時間，通過PrintWriter的println函數發送給客戶端，最后推出循環。

同步阻塞式IO創建的TimeClient源碼分析

public class TimeClient {
    public static void main(String[] args) {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
                //
            }
        }

        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;

        try {
            socket = new Socket("127.0.0.1", port);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
            out.println("QUERY TIME ORDER");
            System.out.println("Send order 2 server succeed.");
            String resp = in.readLine();
            System.out.println("Now is:" + resp);
        } catch (Exception e) {

        } finally {
            if (out != null) {
                out.close();
                out = null;
            }
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                in = null;
            }
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                socket = null;
            }
        }
    }
}