興大物件導向程式設計 Assignment Ch28 參考詳解

28.3#

Distinguish between connection-oriented and connectionless network services.

Connection-oriented network services
- 在傳輸數據前必須先建立連接（eg. TCP）
- 數據傳輸穩定可靠，可以確保傳輸的數據按順序到達、完整傳達
Connectionless network services
- 直接發送數據，不需要先建立連接（eg. UDP）
- 數據可能會丟失、重覆、亂序送達

28.4#

How does a client determine the host name of the client computer?

可以從電腦的設定中查看，也可以用 Java 程式取得：

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import java.net.InetAddress;
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import java.net.UnknownHostException;
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public class Test {
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    public static void main(String[] args) {
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        try {
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            InetAddress addr = InetAddress.getLocalHost();
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            String hostname = addr.getHostName();
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            System.out.println("Host name: " + hostname);
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        } catch (UnknownHostException e) {
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            e.printStackTrace();
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        }
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    }
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}

輸出結果：

28.5#

Under what circurmstances would a Socket Exception be thrown?

試著連接到一個已關閉的 port（連接埠/端口）
在傳輸數據的過程中，連接意外中斷
網路錯誤導致傳輸失敗
客戶端（Client）或伺服器（Server）的資源耗盡

28.6#

How can a client get a line of text from a server?

客戶端透過 Socket 連接到 Server 後，可以使用 BufferedReader 從 InputStream 中讀取文字。假設 Server 的 ip 是 localhost:8080：

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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.net.Socket;
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public class Client {
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    public static void main(String[] args) {
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        try (Socket socket = new Socket("localhost", 8080);
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                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
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            String line;
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            while ((line = in.readLine()) != null) {
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                System.out.println(line);
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            }
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        } catch (Exception e) {
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            e.printStackTrace();
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        }
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    }
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}

28.7#

Describe how a client connects to a server.

一樣假設 Server 的 ip 是 localhost:8080：

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import java.net.Socket;
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public class Client {
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    public static void main(String[] args) {
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        try (Socket socket = new Socket("localhost", 8080)) {
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            System.out.println("Connected to the server");
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        } catch (Exception e) {
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            e.printStackTrace();
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        }
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    }
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}

28.8#

Describe how a server sends data to a client.

伺服器可以使用 OutputStream 向已連接的 Client 發送數據：

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import java.io.OutputStream;
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import java.net.ServerSocket;
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import java.net.Socket;
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public class Server {
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    public static void main(String[] args) {
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        try (ServerSocket serverSocket = new ServerSocket(8000)) {
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            System.out.println("Server is listening on port 8000");
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            Socket socket = serverSocket.accept();
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            OutputStream out = socket.getOutputStream();
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            out.write("Hello, Client".getBytes());
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            out.flush();
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        } catch (Exception e) {
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            e.printStackTrace();
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        }
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    }
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}

28.9#

Describe how to prepare a server to receive a stream-based connection from a single client.

創建一個 ServerSocket 的 Object，綁定到指定的 Port
調用 accept() 方法，等待 client 連接
獲取到 Socket Object 後，通過 InputStream 和 OutputStream 進行數據傳輸

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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.net.ServerSocket;
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import java.net.Socket;
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public class SingleClientServer {
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    public static void main(String[] args) {
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        try (ServerSocket serverSocket = new ServerSocket(8080)) {
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            System.out.println("Server is listening on port 8080");
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            Socket socket = serverSocket.accept();
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            System.out.println("Client connected");
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            // 使用 BufferedReader 和 PrintWriter 傳輸數據
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            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
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            String clientMessage;
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            while ((clientMessage = in.readLine()) != null) {
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                System.out.println("Client says: " + clientMessage);
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            }
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            socket.close();
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            System.out.println("Client disconnected");
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        } catch (Exception e) {
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            e.printStackTrace();
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        }
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    }
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}

28.10#

How does a server listen for stream-based socket connections at a port?

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package anytime;
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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.io.PrintWriter;
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import java.net.ServerSocket;
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import java.net.Socket;
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public class Server {
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    public static void main(String[] args) {
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        try (ServerSocket serverSocket = new ServerSocket(8000)) {
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            System.out.println("Server is listening on port 8000");
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            while (true) {
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                Socket socket = serverSocket.accept();
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                System.out.println("New client connected: " + socket.getInetAddress());
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                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
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                PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
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                String clientMessage;
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                while ((clientMessage = in.readLine()) != null) {
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                    System.out.println("Client says: " + clientMessage);
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                    out.println("Server received: " + clientMessage);
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                }
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                socket.close();
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                System.out.println("Client disconnected: " + socket.getInetAddress());
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            }
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        } catch (Exception e) {
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            e.printStackTrace();
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        }
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    }
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}

28.13#

Write an JAVA application and use a socket connection to allow a cliet to specify a filename of a text file (test.txt) and have the server send the concents of the file or indicate that the file does not exist.

程式碼（Github）：傳送門

執行結果：

歹喙斗 PytreeDao