Android 客戶端對接伺服器入門：從 Servlet 到資料庫

完成 Android 客戶端後，需建立伺服器接收資料。最簡單路徑：Java + Tomcat + Servlet + MySQL，無需複雜框架即可快速驗證流程。

極簡架構圖

Android App (HttpURLConnection/OkHttp/Retrofit)
        ↓ HTTP POST/GET (JSON)
Tomcat Servlet (doPost/doGet)
        ↓ JDBC
MySQL Database

伺服器端核心程式碼

@WebServlet("/api/data")
public class DataServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        // 1. 讀取 JSON
        StringBuilder sb = new StringBuilder();
        try (BufferedReader br = req.getReader()) {
            String line;
            while ((line = br.readLine()) != null) sb.append(line);
        }
        JSONObject json = new JSONObject(sb.toString());

        // 2. 寫入資料庫
        try (Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
             PreparedStatement ps = conn.prepareStatement(
                     "INSERT INTO records (content, created_at) VALUES (?, NOW())")) {
            ps.setString(1, json.getString("content"));
            ps.executeUpdate();
            resp.setStatus(HttpServletResponse.SC_OK);
            resp.getWriter().write("{\"status\":\"success\"}");
        } catch (SQLException e) {
            resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e.getMessage());
        }
    }
}

Android 端呼叫範例

OkHttpClient client = new OkHttpClient();
JSONObject json = new JSONObject().put("content", "測試資料");
RequestBody body = RequestBody.create(json.toString(), MediaType.get("application/json"));
Request request = new Request.Builder()
        .url("https://your-server:8080/api/data")
        .post(body)
        .build();
client.newCall(request).enqueue(new Callback() {
    @Override public void onResponse(Call call, Response response) {
        Log.d("Server", response.body().string());
    }
    @Override public void onFailure(Call call, IOException e) {
        Log.e("Server", "請求失敗", e);
    }
});

進階演進方向

• 引入連線池：HikariCP 或 Druid。
• 採用框架：Spring Boot、MyBatis、JPA 簡化開發。
• 安全強化：JWT 驗證、HTTPS、輸入驗證、SQL 注入防護。
• 非同步處理：CompletableFuture、訊息佇列（RabbitMQ/Kafka）削峰填谷。

先跑通最簡流程，再按需求逐步重構，是穩健的工程實踐。