Android之JSON格式數據解析

JSON：JavaScript 對象表示法（JavaScript Object Notation）。獨立於語言和平台，比 XML 更小、更快，更易解析。如今JSON數據已經成為了互聯網中大多數數據的傳遞方式，所以必須要熟練掌握。

Android平台自帶了JSON解析的相關API，可以將文件、輸入流中的數據轉化為JSON對象，然后從對象中獲取JSON保存的數據內容。

Android的JSON解析部分都在包org.json下，主要有以下幾個類： 
JSONObject：可以看作是一個json對象,這是系統中有關JSON定義的基本單元，其包含一對兒(Key/Value)數值。它對外部(External：應用toString()方法輸出的數值)調用的響應體現為一個標准的字符串（例如：{"JSON": "Hello, World"}，最外被大括號包裹，其中的Key和Value被冒號":"分隔）。其對於內部(Internal)行為的操作格式略微，例如：初始化一個JSONObject實例，引用內部的put()方法添加數值：new JSONObject().put("JSON", "Hello, World!")，在Key和Value之間是以逗號","分隔。Value的類型包括：Boolean、JSONArray、JSONObject、Number、String或者默認值JSONObject.NULL object。

JSONStringer：json文本構建類 ，根據官方的解釋，這個類可以幫助快速和便捷的創建JSON text。其最大的優點在於可以減少由於 格式的錯誤導致程序異常，引用這個類可以自動嚴格按照JSON語法規則（syntax rules）創建JSON text。每個JSONStringer實體只能對應創建一個JSON text。。其最大的優點在於可以減少由於格式的錯誤導致程序異常，引用這個類可以自動嚴格按照JSON語法規則（syntax rules）創建JSON text。每個JSONStringer實體只能對應創建一個JSON text。

JSONArray：它代表一組有序的數值。將其轉換為String輸出(toString)所表現的形式是用方括號包裹，數值以逗號”,”分隔（例如：[value1,value2,value3]，大家可以親自利用簡短的代碼更加直觀的了解其格式）。這個類的內部同樣具有查詢行為，get()和opt()兩種方法都可以通過index索引返回指定的數值，put()方法用來添加或者替換數值。同樣這個類的value類型可以包括：Boolean、JSONArray、JSONObject、Number、String或者默認值JSONObject.NULL object。

JSONTokener：json解析類
JSONException：json中用到的異常

下面以聚合數據空氣質量城市空氣PM2.5指數數據接口為例來演示JSON格式數據的解析。

聚合數據空氣質量城市空氣PM2.5指數數據接口API文檔參見：http://www.juhe.cn/docs/api/id/33/aid/79
JSON返回示例：

 

{
    "resultcode": "200",
    "reason": "SUCCESSED!",
    "result": [
        {
            "city": "蘇州",  /*城市*/
            "PM2.5": "73",  /*PM2.5指數*/
            "AQI": "98",    /*空氣質量指數*/
            "quality": "良", /*空氣質量*/
            "PM10": "50",/*PM10*/
            "CO": "0.79",  /*一氧化碳*/
            "NO2": "65",  /*二氧化氮*/
            "O3": "28",    /*臭氧*/
            "SO2": "41",  /*二氧化硫*/
            "time": "2014-12-26 11:48:40"/*更新時間*/  
        }
    ],
    "error_code": 0
}

 

實例：JSONDemo
運行效果：

代碼清單：
布局文件：activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical"  
    tools:context=".MainActivity" >  
  
    <LinearLayout   
        android:layout_width="match_parent"  
        android:layout_height="wrap_content"   
        android:orientation="horizontal" >  
  
        <TextView  
            android:layout_width="wrap_content"  
            android:layout_height="wrap_content"  
            android:layout_weight="1"  
            android:gravity="center"  
            android:text="城市："  
            android:textSize="23sp" />  
  
        <EditText   
            android:id="@+id/city"  
            android:layout_width="wrap_content"  
            android:layout_height="wrap_content"  
            android:layout_weight="3"  
            android:inputType="text" />"  
    </LinearLayout>  
  
    <Button  
        android:id="@+id/query"  
        android:layout_width="match_parent"  
        android:layout_height="wrap_content"   
        android:text="查詢"   
        android:textSize="23sp" />  
      
    <TextView  
        android:id="@+id/result"  
        android:layout_width="match_parent"  
        android:layout_height="match_parent" />  
</LinearLayout>  

Java源代碼文件：MainActivity.java

package com.rainsong.jsondemo;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.view.Menu;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
import android.widget.EditText;  
import android.widget.TextView;  
import android.widget.Toast;  
  
public class MainActivity extends Activity {  
    EditText et_city;  
    Button btn_query;  
    TextView tv_result;  
    QueryTask task;  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
  
        et_city = (EditText)findViewById(R.id.city);  
        tv_result = (TextView)findViewById(R.id.result);  
        btn_query = (Button)findViewById(R.id.query);  
  
        btn_query.setOnClickListener(new OnClickListener() {  
            public void onClick(View view) {  
                String city = et_city.getText().toString();  
                if (city.length() < 1) {  
                    Toast.makeText(MainActivity.this, "請輸入城市名",  
                            Toast.LENGTH_LONG).show();  
                    return;  
                }  
                task = new QueryTask(MainActivity.this, tv_result);  
                task.execute(city);  
            }  
        });  
    }  
  
    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        // Inflate the menu; this adds items to the action bar if it is present.  
        getMenuInflater().inflate(R.menu.main, menu);  
        return true;  
    }  
  
} 

Java源代碼文件：QueryTask.java

package com.rainsong.jsondemo;  
  
import java.io.IOException;  
import java.net.URLEncoder;  
import java.util.ArrayList;  
  
import org.apache.http.HttpResponse;  
import org.apache.http.NameValuePair;  
import org.apache.http.client.HttpClient;  
import org.apache.http.client.methods.HttpGet;  
import org.apache.http.impl.client.DefaultHttpClient;  
import org.apache.http.message.BasicNameValuePair;  
import org.apache.http.util.EntityUtils;  
import org.json.JSONArray;  
import org.json.JSONException;  
import org.json.JSONObject;  
  
import android.content.Context;  
import android.os.AsyncTask;  
import android.widget.TextView;  
import android.widget.Toast;  
  
public class QueryTask extends AsyncTask<String, Void, String> {  
    Context context;  
    TextView tv_result;  
  
    private static final String JUHE_URL_ENVIRONMENT_AIR_PM =   
                                    "http://web.juhe.cn:8080/environment/air/pm";  
    private static final String JUHE_APPKEY = "你申請的APPKEY值";  
  
    public QueryTask(Context context, TextView tv_result) {  
        // TODO Auto-generated constructor stub  
        super();  
        this.context = context;  
        this.tv_result = tv_result;   
    }  
  
    @Override  
    protected String doInBackground(String... params) {  
        String city = params[0];  
  
        ArrayList<NameValuePair> headerList = new ArrayList<NameValuePair>();  
        headerList.add(new BasicNameValuePair("Content-Type", "text/html; charset=utf-8"));  
  
        String targetUrl = JUHE_URL_ENVIRONMENT_AIR_PM;  
  
        ArrayList<NameValuePair> paramList = new ArrayList<NameValuePair>();  
        paramList.add(new BasicNameValuePair("key", JUHE_APPKEY));  
        paramList.add(new BasicNameValuePair("dtype", "json"));  
        paramList.add(new BasicNameValuePair("city", city));  
  
        for (int i = 0; i < paramList.size(); i++) {  
            NameValuePair nowPair = paramList.get(i);  
            String value = nowPair.getValue();  
            try {  
                value = URLEncoder.encode(value, "UTF-8");  
            } catch (Exception e) {  
            }  
            if (i == 0) {  
                targetUrl += ("?" + nowPair.getName() + "=" + value);  
            } else {  
                targetUrl += ("&" + nowPair.getName() + "=" + value);  
            }  
        }  
  
        HttpGet httpRequest = new HttpGet(targetUrl);  
        try {  
            for (int i = 0; i < headerList.size(); i++) {  
                httpRequest.addHeader(headerList.get(i).getName(),  
                                        headerList.get(i).getValue());  
            }  
  
            HttpClient httpClient = new DefaultHttpClient();  
  
            HttpResponse httpResponse = httpClient.execute(httpRequest);  
            if (httpResponse.getStatusLine().getStatusCode() == 200) {  
                String strResult = EntityUtils.toString(httpResponse.getEntity());  
                return strResult;  
            } else {  
                return null;  
            }  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
        return null;  
    }  
  
    @Override    
    protected void onPostExecute(String result) {  
        if (result != null) {  
            try {  
                JSONObject jsonObject = new JSONObject(result);  
                int resultCode = jsonObject.getInt("resultcode");  
                if (resultCode == 200) {  
                    JSONArray resultJsonArray = jsonObject.getJSONArray("result");  
                    JSONObject resultJsonObject = resultJsonArray.getJSONObject(0);  
                    String output = context.getString(R.string.city) + ": " + resultJsonObject.getString("city") + "\n"  
                            + context.getString(R.string.PM25) + ": " + resultJsonObject.getString("PM2.5") + "\n"  
                            + context.getString(R.string.AQI) + ": " + resultJsonObject.getString("AQI") + "\n"  
                            + context.getString(R.string.quality) + ": " + resultJsonObject.getString("quality") + "\n"  
                            + context.getString(R.string.PM10) + ": " + resultJsonObject.getString("PM10") + "\n"  
                            + context.getString(R.string.CO) + ": " + resultJsonObject.getString("CO") + "\n"  
                            + context.getString(R.string.NO2) + ": " + resultJsonObject.getString("NO2") + "\n"  
                            + context.getString(R.string.O3) + ": " + resultJsonObject.getString("O3") + "\n"  
                            + context.getString(R.string.SO2) + ": " + resultJsonObject.getString("SO2") + "\n"  
                            + context.getString(R.string.time) + ": " + resultJsonObject.getString("time") + "\n";  
                    tv_result.setText(output);  
                } else if (resultCode == 202) {  
                    String reason = jsonObject.getString("reason");  
                    tv_result.setText(reason);  
                } else {  
                    Toast.makeText(context, "查詢失敗",  
                            Toast.LENGTH_LONG).show();  
                    tv_result.setText("");  
                }  
            } catch (JSONException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
        } else {  
            Toast.makeText(context, "查詢失敗",  
                                    Toast.LENGTH_LONG).show();  
            tv_result.setText("");  
        }  
    }    
    
}  

 字符串資源：string.xml

<?xml version="1.0" encoding="utf-8"?>  
<resources>  
  
    <string name="app_name">JSONDemo</string>  
    <string name="action_settings">Settings</string>  
    <string name="hello_world">Hello world!</string>  
  
    <string name="city">城市</string>  
    <string name="PM25">PM2.5指數</string>  
    <string name="AQI">空氣質量指數</string>  
    <string name="quality">空氣質量</string>  
    <string name="PM10">PM10</string>  
    <string name="CO">一氧化碳</string>  
    <string name="NO2">二氧化氮</string>  
    <string name="O3">臭氧</string>  
    <string name="SO2">二氧化硫</string>  
    <string name="time">更新時間</string>  
      
</resources>  

API知識點
public class 
JSONObject
extends Object

org.json.JSONObject

Class Overview
A modifiable set of name/value mappings. Names are unique, non-null strings. Values may be any mix of JSONObjects, JSONArrays, Strings, Booleans, Integers, Longs, Doubles or NULL. Values may not be null, NaNs, infinities, or of any type not listed here. 

JSONObject(String json) 
Creates a new JSONObject with name/value mappings from the JSON string.
 
Object  get(String name) 
Returns the value mapped by name. 

int  getInt(String name) 
Returns the value mapped by name if it exists and is an int or can be coerced to an int. 

String  getString(String name) 
Returns the value mapped by name if it exists, coercing it if necessary. 

JSONArray  getJSONArray(String name) 
Returns the value mapped by name if it exists and is a JSONArray. 

public class 
JSONArray
extends Object

org.json.JSONArray

Class Overview
A dense indexed sequence of values. Values may be any mix of JSONObjects, other JSONArrays, Strings, Booleans, Integers, Longs, Doubles, null or NULL. Values may not be NaNs, infinities, or of any type not listed here. 

JSONObject  getJSONObject(int index) 

Returns the value at index if it exists and is a JSONObject.