来自Google官方的关于Android的JSON解析示例，如果远程服务器使用了json而不是xml，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, booleanexpandTemplates)
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。
