使用 Java 連上 PTT

因為需要嘗試透過 Telnet 登入 PTT，雖然理論上覺得 PTT 的 Android App 這麼多，應該不會找不到可以引用的 Open Source
但實際找了，好像還真的找不太到 @@
最後是參考了 Github 上的一個開源專案 [1]，擷取了其中連線和取得畫面的部份作為這次的實驗～。

與 PTT 建立連線

在建立連線的部份，[1] 的描述是說如果是 Telnet 可以使用 Apache Commons Net [2]，SSH 則可以使用 JSch [3]
本來是要直接實驗連 ptt.cc:443 的，但結果失敗了 XD
因此這段擷取的範例是用 Telnet 來實作。

使用 Apache Commons Net 與 PTT 建立連線

建立連線其實非常簡單，只要用 org.apache.commons.net.telnet.TelnetClient 指定跟 PTT 連線就好。程式碼如下：

private TelnetClient telnetClient = new TelnetClient();

public void connect() throws IOException {
    this.telnetClient.connect("ptt.cc");
}

取得 PTT 回覆的內容

在上面的 TelnetClient 建立連線後，可以取得 InputStream 和 OutputStream，用來取得回應以及發送指令
因為目前是要先取得 PTT 首頁的畫面，因此需要的是 InputStream 的部份。

public List<String> getScreen() throws IOException {
  LinkedList<String> screenLines = new LinkedList<String>();
  try (
      // Read the response in Big5 since PTT respond Big5 characters when
      // using telnet.
      InputStreamReader isr =
          new InputStreamReader(this.telnetClient.getInputStream(), "Big5");
      BufferedReader br = new BufferedReader(isr);
      PushbackReader pbr = new PushbackReader(br, 128)) {

    int length = 0;
    char[] buffer = new char[4096];
    while ((length = pbr.read(buffer)) != -1) {
      StringBuilder sb = new StringBuilder();
        
      // Collect and parse the response from the terminal.
      for (int pos = 0; pos < length; pos++) {
        char c = buffer[pos];

        switch (c) {
          case 0x0A: // LF
            screenLines.add(sb.toString());
            sb.setLength(0);
            break;
          case 0x0D: // CR
          case 0x1B: // ESC
            break;
          default:
            if (c < 0x20 || c == 0x7F) {
              break;
            }
            sb.append(String.valueOf(c));
        }
      }
        
      return screenLines;
    }
  }
}

這裡我把原本 [1] 的程式碼簡化了非常多的地方，因為目前我只是想實驗把畫面印出來看看而已 XD
所以本來回覆的共 4096 個 character，被我直接轉存成 String List
而轉存過程中做的檢查，也只有檢查是否該換行，然後其他似乎是非必要的控制碼就都略過了。

印出取得的回覆

取得回覆以後，第一件事自然是想看看到底拿到什麼東西了
因為上面已經把資料轉存成 String List 了，所以其實印出來…就只是尋訪 List 的每個字串而已囉 XD。

public void printScreen (List<string> screenLines) {
  log.trace("Screen ({} lines):", screenLines.size());
  for (String line : screenLines) {
    log.trace("Line: {}", line);
  }
}

然後我的實驗程式印出來的結果是這樣：

2016-12-27 15:35:28,088 | Screen (31 lines):
2016-12-27 15:35:28,089 | Line: HTTP/1.1 200 OK
2016-12-27 15:35:28,089 | Line: 
2016-12-27 15:35:28,089 | Line:      ˙      [33;1mPTT[m                ·   ◣        ·  ˙      [1m◢[47m██████[40m◤[m
2016-12-27 15:35:28,089 | Line:              [1m140.112.172.11 [m·     ◢[47m█[1m◥[40m█◤[m            [1m◢[47m█████[m
2016-12-27 15:35:28,089 | Line:   ┌─┐     [33;1m批踢踢實業坊[m        ◢[30;47m▃[37m██[1m◥█[40m◤[m   ·   [1m◢[47m█████[40m◤  [m·[m
2016-12-27 15:35:28,089 | Line:   │[1m–[m└┐   [1mptt.cc       [m     ◢[47m█████[1m◥[40m█◤[m    [1m◢[47m█████[m
2016-12-27 15:35:28,089 | Line:   │[1m–[m  │                   ◢[47m███[40m◤[47m███[1m◥[40m◤[m  [1m◢[47m█████[40m◤  [m˙  ·[m
2016-12-27 15:35:28,089 | Line: ─┘    │┌──┐  ·       ◥◤      [47m████[40m◣[1m◢[47m████[40m    [m·[m
2016-12-27 15:35:28,089 | Line:         └┤  [33;1m–[m│      ·           ◢[47m████[1m◢███[40m◤            [m·[m
2016-12-27 15:35:28,089 | Line:                 │┌───┐         [47m█████[40m▇▇▆▆▅▅▄▄▃▂▁[m
2016-12-27 15:35:28,089 | Line:             ┌─┴┘[1m–[33m–[m  └ ◢[47m█████[40m▇▇▆▆▅▅▄▄▃▃▂▂▁[m
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參考資料

1. g21589/PTTCrawler
2. Apache Commons Net
3. JSch