httpConnectionPost 實作
===

- `HttpUtils.java`

- 使用一個 Util 類別來處理 http 的連線，接收兩參數：
- `apiUrl` 為 server domain，`string` 格式，Ex：`http://192.168.1.100:8000/rest/test`
- `jString` 為自定義物件的 `string` 格式，透過 **[Gson](https://github.com/google/gson)** 將物件轉成 `string`
- 結果回傳 `string` 格式，再透過 **Gson** 將 `string` 轉成自定義物件

public class HttpUtils {
    private static Logger logger = LoggerFactory.getLogger(FileViewerUtils.class.getName());

    public static String httpConnectionPost(String apiUrl, String jString) {
        HttpURLConnection conn = null;
        StringBuilder response = new StringBuilder();

        try {
            // server domain
            URL url = new URL(apiUrl);

            // 建立要連線的 HttpURLConnection 物件
            conn = (HttpURLConnection) url.openConnection();

            // 設定 Header 參數
            conn.setRequestProperty("Content-Type","application/json; charset=UTF-8");
            conn.setRequestProperty("Accept", "application/json");

            // 設定連線方法
            conn.setRequestMethod("POST");

            // 設定雙向溝通
            conn.setDoInput(true);  // app 端是否接收 server 的回傳結果
            conn.setDoOutput(true); // app 端是否傳送資料給 server; if true, connection 會自動將 RequestMethod 設為 POST

            // 設定等待時間(ms). 等待時間到若 server 無回應則會跳例外
            conn.setConnectTimeout(5000);

            // 其他參數
            //conn.setReadTimeout(10000);
            //conn.setUseCaches(false);
            
            DataOutputStream os = new DataOutputStream(conn.getOutputStream());

            os.writeBytes(jString);
            os.flush();
            os.close();

            /** Get Response */
            InputStream is = conn.getInputStream();

            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            String line;

            while ((line = reader.readLine()) != null) {
                response.append(line);
                response.append('\r');
            }

            reader.close();
        }
        catch (Exception e) {
            logger.error(String.valueOf(e));
        }
        finally {
            if(conn != null) {
                // 關閉連線
                conn.disconnect();
            }
        }

        return response.toString();
    }
}

## Ref.
[[Android]HttpURLConnection 之POST&GET手把手完整教學解析](https://medium.com/%E4%B8%80%E8%B5%B7%E5%8B%95%E6%89%8B%E5%81%9Aandroidapp/android-%E4%BD%BF%E7%94%A8httpurlconnection-%E9%80%B2%E8%A1%8Cpost-get%E9%80%A3%E7%B7%9A-b44c62dedd37)
[Android - HttpURLConnection POST Json](https://dotblogs.com.tw/newmonkey48/2017/09/21/152425)
[Android网络之HttpUrlConnection和Socket关系图解](https://blog.51cto.com/u_15758326/5610706)
###### tags: `實作相關`