//下面KKState類實現了一個有趣的對話過程的主要流程：用戶啟動服務程序，服務程序監聽來自網絡的連接請求，
//如果有客戶連接，則建立連接。然后，在客戶終端上顯示"Knock! Knock!"，客戶端如果輸入”Who's there?”，則
//回答"Turnip"。客戶輸入"Turnip who?"，回答"Turnip the heat, it's cold in here! Want another? (y/n)"。如果客戶
//輸入"y"，則進行下一輪新的對話，否則結束。關于對話的內容事先存儲在兩個字符串數組中。
import java.net.*;
import java.io.*;
/**
 * @com.register ( clsid=F8188795-F5FC-11D2-A9DF-000021E9BCD1, typelib=F8188794-F5FC-11D2-A9DF-000021E9BCD1 )
 */
class KKState {
    private static final int WAITING = 0;
    private static final int SENTKNOCKKNOCK = 1;
    private static final int SENTCLUE = 2;
    private static final int ANOTHER = 3;
    private static final int NUMJOKES = 5;
    private int state = WAITING;
    private int currentJoke = 0;

    private String[] clues = { "Turnip", "Little Old Lady", "Atch", "Who", "Who" };
    private String[] answers = { "Turnip the heat, it's cold in here!",
                                 "I didn't know you could yodel!",
                                 "Bless you!",
                                 "Is there an owl in here?",
                                 "Is there an echo in here?" };
    String processInput(String theInput) {
    String theOutput = null;

    if (state == WAITING) {
            theOutput = "Knock! Knock!";
            state = SENTKNOCKKNOCK;
        } else if (state == SENTKNOCKKNOCK) {
            if (theInput.equalsIgnoreCase("Who's there?")) {
                theOutput = clues[currentJoke];
                state = SENTCLUE;
            } else {
                theOutput = "You're supposed to say \"Who's there?\"! Try again. Knock! Knock!";
            }
        } else if (state == SENTCLUE) {
            if (theInput.equalsIgnoreCase(clues[currentJoke] + " who?")) {
                theOutput = answers[currentJoke] + " Want another? (y/n)";
                state = ANOTHER;
            } else {
                theOutput = "You're supposed to say \"" + clues[currentJoke] + " who?\"" + "! Try again. Knock! Knock!";
                state = SENTKNOCKKNOCK;
            }
        } else if (state == ANOTHER) {
            if (theInput.equalsIgnoreCase("y")) {
                theOutput = "Knock! Knock!";
                if (currentJoke == (NUMJOKES - 1))
                    currentJoke = 0;
                else
                    currentJoke++;
                state = SENTKNOCKKNOCK;
            } else {
                theOutput = "Bye.";
                state = WAITING;
            }
        }
        return theOutput;
    }
}


//服務器程序
/**
 * @com.register ( clsid=F8188796-F5FC-11D2-A9DF-000021E9BCD1, typelib=F8188794-F5FC-11D2-A9DF-000021E9BCD1 )
 */
class KnockKnockServer {
public static void main(String[] args) {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444); //創建服務器端socket
        } catch (IOException e) {
        System.out.println("Could not listen on port: " + 4444 + ", " + e);
        System.exit(1);
        }
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();//監聽申請連接到該socket的要求并建立連接
} catch (IOException e) {
System.out.println("Accept failed: " + 4444 + ", " + e);
System.exit(1);
}
try {
//通過客戶端socket，獲取輸入數據流對象，通過它可以讀入客戶端輸入的信息
//通過客戶端socket，獲取輸出數據流對象，通過它可以向客戶端輸入的信息
DataInputStream is = new DataInputStream(new BufferedInputStream(clientSocket.getInputStream()));
PrintStream os=new PrintStream(new BufferedOutputStream(clientSocket.getOutputStream(), 1024), false);
//KKState類用于處理輸入的會話信息，然后返回設定好的回答
KKState kks = new KKState();
String inputLine, outputLine;

     outputLine = kks.processInput(null);
     os.println(outputLine);//第一次運行，輸入參數為null，kks返回："Knock! Knock!"；然后向客戶端寫入。
     os.flush();
	//如果客戶端沒有輸入，readLine將阻塞；如果客戶端關閉，readLine返回為null。
	//在下面循環語句中，以讀一行，再寫一行的方式與客戶交互。
     while ((inputLine = is.readLine()) != null) {
		System.out.println("cli:"+inputLine);
		outputLine = kks.processInput(inputLine);
		os.println(outputLine);
        os.flush();
          if (outputLine.equals("Bye.")) break;
      }
//以下完成清除工作。
     os.close();
     is.close();
     clientSocket.close();
     serverSocket.close();
     } catch (IOException e) {
     	e.printStackTrace();
     }
    }
}