Android之JSON格式數據解析
來源：程序員人生 發布時間：2015-01-07 08:13:08 閱讀次數：4808次
JSON：JavaScript 對象表示法（JavaScript Object Notation）。獨立于語言和平臺，比 XML 更小、更快，更容易解析。如今JSON數據已成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平臺自帶了JSON解析的相干API，可以將文件、輸入流中的數據轉化為JSON對象，然后從對象中獲得JSON保存的數據內容。
Android的JSON解析部份都在包org.json下，主要有以下幾個類：
JSONObject：可以看做是1個json對象,這是系統中有關JSON定義的基本單元，其包括1對兒(Key/Value)數值。它對外部(External：利用toString()方法輸出的數值)調用的響應體現為1個標準的字符串（例如：{"JSON": "Hello, World"}，最外被大括號包裹，其中的Key和Value被冒號":"分隔）。其對內部(Internal)行動的操作格式稍微，例如：初始化1個JSONObject實例，援用內部的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或默許值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。其最大的優點在于可以減少由于 格式的毛病致使程序異常，援用這個類可以自動嚴格依照JSON語法規則（syntax rules）創建JSON text。每一個JSONStringer實體只能對應創建1個JSON text。。其最大的優點在于可以減少由于格式的毛病致使程序異常，援用這個類可以自動嚴格依照JSON語法規則（syntax rules）創建JSON text。每一個JSONStringer實體只能對應創建1個JSON
text。
JSONArray：它代表1組有序的數值。將其轉換為String輸出(toString)所表現的情勢是用方括號包裹，數值以逗號”,”分隔（例如：[value1,value2,value3]，大家可以親身利用簡短的代碼更加直觀的了解其格式）。這個類的內部一樣具有查詢行動，get()和opt()兩種方法都可以通過index索引返回指定的數值，put()方法用來添加或替換數值。一樣這個類的value類型可以包括：Boolean、JSONArray、JSONObject、Number、String或默許值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：
{ /*JSONObject*/
"resultcode": "200",
"reason": "SUCCESSED!",
"result": [ /*JSONArray*/
{ /*JSONObject*/
"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", /*1氧化碳*/
"NO2": "65", /*2氧化氮*/
"O3": "28", /*臭氧*/
"SO2": "41", /*2氧化硫*/
"time": "2014⑴2⑵6 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=utf⑻"));
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, "UTF⑻");
} 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") + "
"
+ context.getString(R.string.PM25) + ": " + resultJsonObject.getString("PM2.5") + "
"
+ context.getString(R.string.AQI) + ": " + resultJsonObject.getString("AQI") + "
"
+ context.getString(R.string.quality) + ": " + resultJsonObject.getString("quality") + "
"
+ context.getString(R.string.PM10) + ": " + resultJsonObject.getString("PM10") + "
"
+ context.getString(R.string.CO) + ": " + resultJsonObject.getString("CO") + "
"
+ context.getString(R.string.NO2) + ": " + resultJsonObject.getString("NO2") + "
"
+ context.getString(R.string.O3) + ": " + resultJsonObject.getString("O3") + "
"
+ context.getString(R.string.SO2) + ": " + resultJsonObject.getString("SO2") + "
"
+ context.getString(R.string.time) + ": " + resultJsonObject.getString("time") + "
";
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="utf⑻"?>
<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">1氧化碳</string>
<string name="NO2">2氧化氮</string>
<string name="O3">臭氧</string>
<string name="SO2">2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.
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