GPS辅助数据下载工具

辅助数据下载实现

• 在GPS内容提供者一节，我们分析了对于辅助信息的处理是通过GpsXtraDownloader类来完成，该类需要从gps.conf的配置文件中得到下载地址，并通过AndroidHttpClient实现数据的下载功能。
• 该类也可作为Http协议下载的范例来学习。

GpsXtraDownloader

GpsXtraDownloader(Context context, Properties properties) {
    mContext = context;

    // 读取服务器地址
    int count = 0;
    String server1 = properties.getProperty("XTRA_SERVER_1");
    String server2 = properties.getProperty("XTRA_SERVER_2");
    String server3 = properties.getProperty("XTRA_SERVER_3");
    if (server1 != null) count++;
    if (server2 != null) count++;
    if (server3 != null) count++;
    
    if (count == 0) {
        return;
    } else {
        mXtraServers = new String[count];
        count = 0;
        if (server1 != null) mXtraServers[count++] = server1;
        if (server2 != null) mXtraServers[count++] = server2;
        if (server3 != null) mXtraServers[count++] = server3;

        // randomize first server
        Random random = new Random();
        mNextServerIndex = random.nextInt(count);
    }       
}

downloadXtraData

byte[] downloadXtraData() {
    String proxyHost = Proxy.getHost(mContext);
    int proxyPort = Proxy.getPort(mContext);
    byte[] result = null;
    ...... 

    while (result == null) {
        // 调用doDownload处理下载任务
        result = doDownload(mXtraServers[mNextServerIndex], useProxy, proxyHost, proxyPort);
        ......    
    }

    return result;
}

doDownload

protected static byte[] doDownload(String url, boolean isProxySet, 
                                   String proxyHost, int proxyPort) {
    AndroidHttpClient client = null;
    try {
        // 创建AndroidHttpClient实例
        client = AndroidHttpClient.newInstance("Android");
        // 创建请求对象
        HttpUriRequest req = new HttpGet(url);

        // 如果需要，创建代理服务
        if (isProxySet) {
            HttpHost proxy = new HttpHost(proxyHost, proxyPort);
            ConnRouteParams.setDefaultProxy(req.getParams(), proxy);
        }

        // 添加请求头信息
        req.addHeader(
                "Accept",
                "*/*, application/vnd.wap.mms-message, application/vnd.wap.sic");

        req.addHeader(
                "x-wap-profile",
                "http://www.openmobilealliance.org/tech/profiles/UAPROF/ccppschema-20021212#");

        // 执行请求，并获取HttpResponse对象
        HttpResponse response = client.execute(req);
        // 获取状态码
        StatusLine status = response.getStatusLine();
        if (status.getStatusCode() != 200) { // HTTP 200 is success.
            if (DEBUG) Log.d(TAG, "HTTP error: " + status.getReasonPhrase());
            return null;
        }

        // 获取HttpEntity对象，并读取返回信息
        HttpEntity entity = response.getEntity();
        byte[] body = null;
        if (entity != null) {
            try {
                if (entity.getContentLength() > 0) {
                    body = new byte[(int) entity.getContentLength()];
                    DataInputStream dis = new DataInputStream(entity.getContent());
                    try {
                        dis.readFully(body);
                    } finally {
                        try {
                            dis.close();
                        } catch (IOException e) {
                            Log.e(TAG, "Unexpected IOException.", e);
                        }
                    }
                }
            } finally {
                if (entity != null) {
                    entity.consumeContent();
                }
            }
        }
        return body;
    } catch (Exception e) {
        if (DEBUG) Log.d(TAG, "error " + e);
    } finally {
        if (client != null) {
            client.close();
        }
    }
    return null;
}