OkHttpPost.java

        String result = null;
        RequestBody body = new FormEncodingBuilder()
                .addEncoded("key1", "value1")
                .addEncoded("key2", "value2")
                .addEncoded("key3", "value3")
                .build();

        // リクエストオブジェクトを作って
        Request request = new Request.Builder()
                .url(base_url)
                .header("Authorization", credential)
                .post(body)
                .build();

        // クライアントオブジェクトを作って
        OkHttpClient client = new OkHttpClient();
            
        // リクエストして結果を受け取って
        try {
            Response response = client.newCall(request).execute();
            if (response.isSuccessful()){
                result = response.body().string();
                Log.d("hoge", "doPost success");
            }
        } catch (IOException e) {
            e.printStackTrace();
            Log.e("hoge", "error orz:" + e.getMessage(), e);
        }

        // 返す
        return result;