Android JSON解析示例代碼

來自Google官方的有關android平台的JSON解析示例，如果遠程服務器使用了JSon而不是XML的數據提供，在Android平台上已經內置的org.json包可以很方便的實現手機客戶端的解析處理。下面Android123一起分析下這個例子，幫助android開發者需要有關 HTTP通訊、正則表達式、JSON解析、appWidget開發的一些知識。

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中開了個服務
    }

    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); //正則表達式處理，有關定義見下面的SimpleWikiHelper類
            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)); //這裡是打開相應的網頁，所以Uri是http的url，action是vIEw即打開web浏覽器
                PendingIntent pendingIntent = PendingIntent.getActivity(context,
                        0 /* no requestCode */, defineIntent, 0 /* no flags */);
                updateVIEws.setOnClickPendingIntent(R.id.widget, pendingIntent); //單擊Widget打開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;
        }
    }
}

  有關網絡通訊的實體類，以及一些常量定義如下:

  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); //設置客戶端標識

        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(); //獲取HTTP返回的數據流

            ByteArrayOutputStream content = new ByteArrayOutputStream();

            int readBytes = 0;
            while ((readBytes = inputStream.read(sBuffer)) != -1) {
                content.write(sBuffer, 0, readBytes); //轉化為字節數組流
            }

            return new String(content.toByteArray()); //從字節數組構建String
        } catch (IOException e) {
            throw new ApIException("Problem communicating with API", e);
        }
    }
}

 有關整個每日維基的widget例子比較簡單，主要是幫助大家積累常用代碼，了解android平台 JSON的處理方式，畢竟很多Server還是Java的。