19. Android简单示例_教你设计物联网系统

由于在某些嵌入式系统中使用的是Android系统，这里给出一个简单的Android App的示例，具体代码可以从clone自https://github.com/phodal/iot-android

代码说明，经过测试的版本有

Android 2.3
Android 4.0.4

机型有

HTC G1 (android 2.3)
Motor xt300 (android 2.3)
Sony ST25I (android 4.0.4)
MI2

应该可以在大部分的手机上工作。

19.1 调用Web Services GET

这里我们参考一篇文章来调用Web Services——Calling Web Services in Android using HttpClient

19.1.1 创建RESTClient

在这里我们首先会定义四个REST方法GET、POST、PUT、DELETE

public void Execute(RequestMethod method) throws Exception {
    switch (method) {
    case GET: {
        // add parameters
        String combinedParams = "";
        if (!params.isEmpty()) {
            combinedParams += "?";
            for (NameValuePair p : params) {
                String paramString = p.getName() + "="
                        + URLEncoder.encode(p.getValue(), HTTP.UTF_8);
                if (combinedParams.length() > 1) {
                    combinedParams += "&" + paramString;
                } else {
                    combinedParams += paramString;
                }
            }
        }
        HttpGet request = new HttpGet(url + combinedParams);
        request.addHeader("Accept-Encoding", "gzip");
        // add headers
        for (NameValuePair h : headers) {
            request.addHeader(h.getName(), h.getValue());
        }
        executeRequest(request, url);
        break;
    }
    case POST: {
        HttpPost request = new HttpPost(url);
        request.addHeader("Accept-Encoding", "gzip");
        // add headers
        for (NameValuePair h : headers) {
            request.addHeader(h.getName(), h.getValue());
        }
        if (!data.equals("")) {
            request.setEntity(new StringEntity(data, HTTP.UTF_8));
        }
        if (!params.isEmpty()) {
            request.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));
        }
        executeRequest(request, url);
        break;
    }
    case PUT: {
        HttpPut request = new HttpPut(url);
        request.addHeader("Accept-Encoding", "gzip");
        // add headers
        for (NameValuePair h : headers) {
            request.addHeader(h.getName(), h.getValue());
        }
        if (!data.equals("")) {
            request.setEntity(new StringEntity(data, HTTP.UTF_8));
        }
        if (!params.isEmpty()) {
            request.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));
        }
        executeRequest(request, url);
        break;
    }
    case DELETE: {
        HttpDelete request = new HttpDelete(url);
        request.addHeader("Accept-Encoding", "gzip");
        // add headers
        for (NameValuePair h : headers) {
            request.addHeader(h.getName(), h.getValue());
        }
        executeRequest(request, url);
        break;
    }
    }
}

这四个方法最后都执行executeRequest来获取响应结果。

protected void executeRequest(HttpUriRequest request, String url) {
        HttpParams httpParameters = new BasicHttpParams();
        HttpConnectionParams.setConnectionTimeout(httpParameters,
                timeoutConnection);
        HttpConnectionParams.setSoTimeout(httpParameters, timeoutSocket);
  
        HttpProtocolParams.setUseExpectContinue(httpParameters, false);
        request.setParams(httpParameters);
  
        setOauth(request);
  
        DefaultHttpClient client = new DefaultHttpClient();
        HttpResponse httpResponse;
        try {
            httpResponse = client.execute(request);
            responseCode = httpResponse.getStatusLine().getStatusCode();
            message = httpResponse.getStatusLine().getReasonPhrase();
            HttpEntity entity = httpResponse.getEntity();
            if (entity != null) {
                InputStream instream = httpResponse.getEntity().getContent();
                Header contentEncoding = httpResponse
                        .getFirstHeader("Content-Encoding");
                if (contentEncoding != null
                        && contentEncoding.getValue().equalsIgnoreCase("gzip")) {
                    instream = new GZIPInputStream(instream);
                }
                // instream = entity.getContent();
                response = convertStreamToString(instream);
                // Closing the input stream will trigger connection release
                instream.close();
            }
        } catch (ClientProtocolException e) {
            client.getConnectionManager().shutdown();
            e.printStackTrace();
        } catch (IOException e) {
            client.getConnectionManager().shutdown();
            e.printStackTrace();
        }
    }

接着，我们便可以执行getResponse()函数来获取结果。

19.2 使用REST Client获取结果

使用RESTClient时，便可以用下面的示例

RestClient client = new RestClient(tUrl);
try {
    client.Execute(RequestMethod.GET);
    if (client.getResponseCode() != 200) {
        //do something
    }
    //JSONArray jArray = new JSONArray(client.getResponse());
} catch (Exception e) {
    //do something
}

而这时，我们只需要对相应的数据进行处理就可以了，如

JSONArray jArray = new JSONArray(client.getResponse());
JSONObject jObj=jArray.getJSONObject(0);
vshow.setText(jObj.toString());
outputJSON(jObj);

将他转换为String，接着在Android端上显示最后的结果。

下一节：设计物联网系统是件有意思的事情，它需要考虑到软件、硬件、通讯等多个不同方面。通过探索不同的语言，不同的框架，从而形成不同的解决方案。