使用 HttpURLConnection 呼叫 WebService

public String postRequest(String requestURL, JSONObject postDataParams) {

        URL url;
        String response = "";
        try {

            url = new URL(requestURL);

            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(30000);
            conn.setConnectTimeout(30000);
            conn.setRequestMethod("POST");
            conn.setDoInput(true);
            //== 設置此設定，才會真正的使用POST方式，反之 GET 時需改為 false
            conn.setDoOutput(true);

            String message = postDataParams.toString();

            conn.setFixedLengthStreamingMode(message.getBytes().length);

            //make some HTTP header nicety
            conn.setRequestProperty("Content-Type", "application/json;charset=utf-8");
            conn.setRequestProperty("X-Requested-With", "XMLHttpRequest");

            //open
            conn.connect();

            //setup send
            OutputStream os = new BufferedOutputStream(conn.getOutputStream());
            os.write(message.getBytes());
            //clean up
            os.flush();

            os.close();

            int responseCode = conn.getResponseCode();

            if (responseCode == HttpsURLConnection.HTTP_OK) {
                String line;
                BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                while ((line = br.readLine()) != null) {
                    response += line;
                }
            } else {
                response = "";

            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        return response;
}

private void callApi() {

    String res = postRequest(requestURL, postDataParams);

    // 轉為 JSONObject
    JSONObject jObj = new JSONObject(res);

}

使用 Volley 呼叫 WebService

Android呼叫Web Service請若非處理大量資料時，可使用Volley，此為Google所開發的一套網路框架，把Http請求和執行緒封裝起來，開發者可簡單的呼叫與使用。若需處理大量資料的話，仍需使用HttpURLConnection，並配合前項說明的AsyncTask來處理流程。

若需使用請在Gradle中設定下列參數

compile 'com.android.volley:volley:1.0.0'

建立JsonObject請求

final String url = "http://test.com/api/hello";

JSONObject params = new JSONObject();
params.put("name", "Polory");
params.put("age", "10");

    // 建立Request
JsonObjectRequest getRequest = new JsonObjectRequest(
    Request.Method.GET, url, null,

    new Response.Listener<JSONObject>() {
        @Override
        public void onResponse(JSONObject response) {
            Log.d("Response", response.toString());        
    }},

    new Response.ErrorListener() {         
        @Override         
        public void onErrorResponse(VolleyError error) {
            Log.d("Error.Response", response);
    }});

建立StringObject請求

StringRequest stringRequest = new StringRequest(
    Request.Method.POST, url, 

    new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            Log.d("Response", response);
        }},

    new Response.ErrorListener() {         
        @Override         
        public void onErrorResponse(VolleyError error) {
            Log.d("Error.Response", response);
    }})
        {
            @Override
            protected Map<String, String> getParams()
            {
                Map<String, String>  params = new HashMap<String,String>();
                params.put("name", "Polory");
                params.put("age", "10");
                return params;
            }
        };