Android JSON解析示例代码

来自Google官方的有关Android平台的JSON解析示例，如果远程服务器使用了json而不是xml的数据提供，在Android平台上已经内置的org.json包可以很方便的实现手机客户端的解析处理。下面Android123一起分析下这个例子，帮助Android开发者需要有关 HTTP通讯、正则表达式、JSON解析、appWidget开发的一些知识。

public class WordWidget extends AppWidgetProvider { //appWidget
@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager,
int[] appWidgetIds) {

context.startService(new Intent(context, UpdateService.class)); //避免ANR，所以Widget中开了个服务
}

public static class UpdateService extends Service {
@Override
public void onStart(Intent intent, int startId) {
// Build the widget update for today
RemoteViews updateViews = buildUpdate(this);

ComponentName thisWidget = new ComponentName(this, WordWidget.class);
AppWidgetManager manager = AppWidgetManager.getInstance(this);
manager.updateAppWidget(thisWidget, updateViews);
}

public RemoteViews buildUpdate(Context context) {
// Pick out month names from resources
Resources res = context.getResources();
String[] monthNames = res.getStringArray(R.array.month_names);

Time today = new Time();
today.setToNow();

String pageName = res.getString(R.string.template_wotd_title,
monthNames[today.month], today.monthDay);
RemoteViews updateViews = null;
String pageContent = "";

try {

SimpleWikiHelper.prepareUserAgent(context);
pageContent = SimpleWikiHelper.getPageContent(pageName, false);
} catch (ApiException e) {
Log.e("WordWidget", "Couldn't contact API", e);
} catch (ParseException e) {
Log.e("WordWidget", "Couldn't parse API response", e);
}

Pattern pattern = Pattern.compile(SimpleWikiHelper.WORD_OF_DAY_REGEX); //正则表达式处理，有关定义见下面的SimpleWikiHelper类
Matcher matcher = pattern.matcher(pageContent);
if (matcher.find()) {

updateViews = new RemoteViews(context.getPackageName(), R.layout.widget_word);

String wordTitle = matcher.group(1);
updateViews.setTextViewText(R.id.word_title, wordTitle);
updateViews.setTextViewText(R.id.word_type, matcher.group(2));
updateViews.setTextViewText(R.id.definition, matcher.group(3).trim());

String definePage = res.getString(R.string.template_define_url,
Uri.encode(wordTitle));
Intent defineIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(definePage)); //这里是打开相应的网页，所以Uri是http的url，action是view即打开web浏览器
PendingIntent pendingIntent = PendingIntent.getActivity(context,
0 /* no requestCode */, defineIntent, 0 /* no flags */);
updateViews.setOnClickPendingIntent(R.id.widget, pendingIntent); //单击Widget打开Activity

} else {

updateViews = new RemoteViews(context.getPackageName(), R.layout.widget_message);
CharSequence errorMessage = context.getText(R.string.widget_error);
updateViews.setTextViewText(R.id.message, errorMessage);
}
return updateViews;
}

@Override
public IBinder onBind(Intent intent) {
// We don't need to bind to this service
return null;
}
}
}

有关网络通讯的实体类，以及一些常量定义如下:

public class SimpleWikiHelper {
private static final String TAG = "SimpleWikiHelper";

public static final String WORD_OF_DAY_REGEX =
"(?s)\\{\\{wotd\\|(.+?)\\|(.+?)\\|([^#\\|]+).*?\\}\\}";

private static final String WIKTIONARY_PAGE =
"http://en.wiktionary.org/w/api.php?action=query&prop=revisions&titles=%s&" +
"rvprop=content&format=json%s";

private static final String WIKTIONARY_EXPAND_TEMPLATES =
"&rvexpandtemplates=true";

private static final int HTTP_STATUS_OK = 200;

private static byte[] sBuffer = new byte[512];

private static String sUserAgent = null;

public static class ApiException extends Exception {
public ApiException(String detailMessage, Throwable throwable) {
super(detailMessage, throwable);
}

public ApiException(String detailMessage) {
super(detailMessage);
}
}

public static class ParseException extends Exception {
public ParseException(String detailMessage, Throwable throwable) {
super(detailMessage, throwable);
}
}

public static void prepareUserAgent(Context context) {
try {
// Read package name and version number from manifest
PackageManager manager = context.getPackageManager();
PackageInfo info = manager.getPackageInfo(context.getPackageName(), 0);
sUserAgent = String.format(context.getString(R.string.template_user_agent),
info.packageName, info.versionName);

} catch(NameNotFoundException e) {
Log.e(TAG, "Couldn't find package information in PackageManager", e);
}
}

public static String getPageContent(String title, boolean expandTemplates)
throws ApiException, ParseException {

String encodedTitle = Uri.encode(title);
String expandClause = expandTemplates ? WIKTIONARY_EXPAND_TEMPLATES : "";

String content = getUrlContent(String.format(WIKTIONARY_PAGE, encodedTitle, expandClause));
try {

JSONObject response = new JSONObject(content);
JSONObject query = response.getJSONObject("query");
JSONObject pages = query.getJSONObject("pages");
JSONObject page = pages.getJSONObject((String) pages.keys().next());
JSONArray revisions = page.getJSONArray("revisions");
JSONObject revision = revisions.getJSONObject(0);
return revision.getString("*");
} catch (JSONException e) {
throw new ParseException("Problem parsing API response", e);
}
}

protected static synchronized String getUrlContent(String url) throws ApiException {
if (sUserAgent == null) {
throw new ApiException("User-Agent string must be prepared");
}

HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet(url);
request.setHeader("User-Agent", sUserAgent); //设置客户端标识

try {
HttpResponse response = client.execute(request);

StatusLine status = response.getStatusLine();
if (status.getStatusCode() != HTTP_STATUS_OK) {
throw new ApiException("Invalid response from server: " +
status.toString());
}

HttpEntity entity = response.getEntity();
InputStream inputStream = entity.getContent(); //获取HTTP返回的数据流

ByteArrayOutputStream content = new ByteArrayOutputStream();

int readBytes = 0;
while ((readBytes = inputStream.read(sBuffer)) != -1) {
content.write(sBuffer, 0, readBytes); //转化为字节数组流
}

return new String(content.toByteArray()); //从字节数组构建String
} catch (IOException e) {
throw new ApiException("Problem communicating with API", e);
}
}
}

有关整个每日维基的widget例子比较简单，主要是帮助大家积累常用代码，了解Android平台 JSON的处理方式，毕竟很多Server还是Java的。

http://www.android123.com.cn/androidkaifa/664.html

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