J2ME 網路應用開發實戰：HTTP 連線、MVC 架構與執行緒模式完整指南

J2ME 網路基礎

MIDP 強制支援 HTTP，Socket 為選擇性。核心類別在 javax.microedition.io，關鍵為 Connector.open(url) 回傳 Connection 介面，轉型為 HttpConnection 使用。

HTTP POST 完整流程範例

void postViaHttpConnection(String url) throws IOException {
    HttpConnection c = null;
    InputStream is = null;
    OutputStream os = null;
    try {
        c = (HttpConnection) Connector.open(url);
        c.setRequestMethod(HttpConnection.POST);
        c.setRequestProperty("User-Agent", "Profile/MIDP-2.0 Configuration/CLDC-1.0");
        c.setRequestProperty("Content-Type", "application/octet-stream");
        
        os = c.openOutputStream();
        os.write("LIST games\n".getBytes());
        os.flush();
        
        int rc = c.getResponseCode(); // 觸發實際連線與傳送
        if (rc != HttpConnection.HTTP_OK) 
            throw new IOException("HTTP response: " + rc);
        
        is = c.openInputStream();
        String type = c.getType();
        int len = (int) c.getLength();
        
        if (len > 0) {
            byte[] data = new byte[len];
            int read = 0, actual;
            while (read < len && (actual = is.read(data, read, len - read)) != -1)
                read += actual;
            process(data);
        } else {
            int ch;
            while ((ch = is.read()) != -1) process((byte) ch);
        }
    } finally {
        if (is != null) is.close();
        if (os != null) os.close();
        if (c != null) c.close();
    }
}

關鍵實務原則

1. 必須使用獨立執行緒：網路操作阻塞主執行緒會凍結 UI，甚至被系統終止。提供等待動畫提升體驗。
2. 採用 MVC 模式：介面多時，分離 Model(資料/邏輯)、View(Canvas/Form)、Controller(事件分發) 利於維護。
3. 資料協定設計：推薦 POST + DataOutputStream/DataInputStream。發送端 writeUTF()/writeInt()，接收端對應 readUTF()/readInt()，順序必須一致。
4. 錯誤處理：檢查回應碼、捕獲 IOException、ClassCastException，確保資源釋放。

完整專案架構範例

Servlet 伺服器端

public class MyServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {
        DataInputStream dis = new DataInputStream(req.getInputStream());
        String msg = dis.readUTF();
        DataOutputStream dos = new DataOutputStream(resp.getOutputStream());
        dos.writeUTF(msg + "haha");
        dis.close(); dos.close();
    }
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException { doPost(req, resp); }
}

用戶端核心類別

• HttpCommMIDlet：啟動 UIController
• UIController：管理畫面切換、事件分發（EventHandler 執行緒）
• InputCanvas：輸入介面，CommandListener 觸發連線事件
• DisplayCanvas：顯示伺服器回應
• HttpCommHandler：封裝 HTTP 連線、發送/接收、資源關閉邏輯

程式碼關鍵片段：HttpCommHandler

public class HttpCommHandler {
    private String url;
    public HttpCommHandler(String url) { this.url = url; }
    
    public String sendMessage(String msg) throws IOException {
        HttpConnection conn = null;
        DataInputStream in = null;
        DataOutputStream out = null;
        try {
            conn = openConnection();
            out = new DataOutputStream(conn.openOutputStream());
            out.writeUTF(msg);
            out.flush();
            
            in = new DataInputStream(conn.openDataInputStream());
            return in.readUTF();
        } finally {
            closeQuietly(conn, in, out);
        }
    }
    
    private HttpConnection openConnection() throws IOException {
        HttpConnection c = (HttpConnection) Connector.open(url);
        c.setRequestMethod(HttpConnection.POST);
        c.setRequestProperty("Content-Type", "application/octet-stream");
        c.setRequestProperty("User-Agent", System.getProperty("microedition.profiles"));
        return c;
    }
    // closeQuietly 略
}

部署建議

• 伺服器建議 Tomcat + Servlet/JSP
• 用戶端測試真機需注意 GPRS 費用與穩定性
• 生產環境應加入重試機制、逾時設定、憑證驗證（HTTPS）