zoukankan      html  css  js  c++  java
  • Chapter 10 Networking/JSON Services

    <1>JSON Service

      In the previous section, you learned how to consume XML web services by using HTTP to connect to the web server and then obtain the

        results in XML. You also learned how to use DOM to parse the result of the XML document.

      However, manipulating XML documents is a computationally expensive operation for mobile devices, for the following reasons:

      <i> XML documents are lengthy.

        They use tags to embed information, and the size of an XML document can get very big pretty quickly. A large XML document means

          that your device has to use more bandwidth to download it, which translates into higher cost.

      <ii> XML documents are more difficult to process.

        As shown earlier, you have to use DOM to traverse the tree in order to locate the information you want. In addition, DOM itself has

          to build the entire document in memory as a tree structure before you can traverse it. This is both memory and CPU intensive.

      JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write

        It is also easy for machines to parse and generate.

    [
        {
            “appeId”:”1”,
            “survId”:”1”,
           “location”:””,
         “surveyDate”:”2008-03 14”,
         “surveyTime”:”12:19:47”,
         “inputUserId”:”1”,
         “inputTime”:”2008-03-14 12:21:51”,
         “modifyTime”:”0000-00-00 00:00:00”
       },
        {
         “appeId”:”2”,
         “survId”:”32”,
         “location”:””,
         “surveyDate”:”2008-03-14”,
         “surveyTime”:”22:43:09”,
         “inputUserId”:”32”,
         “inputTime”:”2008-03-14 22:43:37”,
         “modifyTime”:”0000-00-00 00:00:00”
       },
       {
         “appeId”:”3”,
         “survId”:”32”,
         “location”:””,
         “surveyDate”:”2008-03-15”,
         “surveyTime”:”07:59:33”,
         “inputUserId”:”32”,
         “inputTime”:”2008-03-15 08:00:44”,
         “modifyTime”:”0000-00-00 00:00:00”
       }
    ] 

      information is represented as a collection of key/value pairs. each key/value pair is grouped into an ordered list of objects. 

      Unlike XML, there are no lengthy tag names, only brackets and braces.

    package mirror.android.jsonservice;
    
    import java.io.BufferedReader;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import org.apache.http.HttpEntity;
    import org.apache.http.HttpResponse;
    import org.apache.http.StatusLine;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.impl.client.DefaultHttpClient;
    import org.json.JSONArray;
    import org.json.JSONException;
    import org.json.JSONObject;
    import android.app.Activity;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.util.Log;
    import android.widget.Toast;
    
    public class JSONActivity extends Activity {
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_json);
            
            new ReadJSONFeedTask().execute("https://twitter.com/statuses/user_timeline/weimenglee.json");
        }
        
        public String ReadJSONFeed(String URL){
            
            StringBuilder stringBuilder = new StringBuilder();
            HttpClient client = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(URL);
            
            try {
                HttpResponse response = client.execute(httpGet);
                StatusLine statusLine = response.getStatusLine();
                int statusCode = statusLine.getStatusCode();
                
                if(statusCode == 200){
                    HttpEntity entity = response.getEntity();
                    InputStream in = entity.getContent();
                    
                    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                    String line;
                    
                    while((line = reader.readLine()) != null){
                        stringBuilder.append(line);
                    }
                }
                else{
                    Log.e("JSON", "Failed to download file");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            return stringBuilder.toString();
        }
        
        private class ReadJSONFeedTask extends AsyncTask<String, Void, String>{
            @Override
            protected String doInBackground(String... urls) {
                return ReadJSONFeed(urls[0]);
            }
    
            @Override
            protected void onPostExecute(String result) {
                try {
                    JSONArray jsonArray = new JSONArray(result);
                    Log.i("JSON", "Number of surveys in feed:" + jsonArray.length());
                    
                    for (int i = 0; i < jsonArray.length(); i++) {
                        JSONObject jsonObject = jsonArray.getJSONObject(i);
                        Toast.makeText(getApplication(), 
                                    jsonObject.getString("text") + " - " + jsonObject.getString("created_at"),
                                    Toast.LENGTH_SHORT).show();
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }
    }
  • 相关阅读:
    调整浏览器兼容性的利器条件判断注释器
    Automatic uninstall IE9 and roll back to IE8
    How to use cmd with C#
    [转]在设计和执行测试用例的时候的几点心得和经验
    Move all files in subfolders to another folder using c#
    数据驱动单元测试实例
    测试web开源项目时如何收集代码覆盖率
    2013春节期间玩CentOS 6.3记录
    当使用ckeditor控件时,需要校验输入内容是否为空的一种解决办法(转帖)
    Enterprise Architect 8.0 注册码
  • 原文地址:https://www.cnblogs.com/iMirror/p/4117266.html
Copyright © 2011-2022 走看看