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我今天在使用 HttpURLConnection 时遇到了这个非常奇怪的事情。我有以下代码，它基本上从 URL 读取数据，并将数据（在使用 GSON 将其解析为 java 对象之后）存储到 Java 对象中。数据也同时存储在另一个我已序列化并保存到文件的对象中。如果我的 URL 不可访问，我会从文件中读取数据。该 URL 是我只能通过 VPN 访问的安全 URL。所以为了测试我的程序，我断开了 VPN 的连接，看看我是否能够从文件中读取数据。下面的第一个代码给我一个空指针，而第二个没有。如您所见，唯一的区别是我在第二个示例中使用了 HttpURLConnection。使用它有什么帮助？有人遇到过类似的事情，还是我忽略了什么？;)

无法访问 URL 时抛出空指针的代码-

public static void getInfoFromURL() throws IOException {
    Gson gson = null;
    URL url = null;
    BufferedReader bufferedReader = null;
    String inputLine = "";
    try {
        gson = new Gson();
        url = new URL(addressURL);
        bufferedReader = new BufferedReader(new InputStreamReader(url.openStream()));
        while ((inputLine = bufferedReader.readLine()) != null) {
            addressData = ((AddressData) gson.fromJson(inputLine,AddressData.class));               
        }                   

    } catch (MalformedURLException mue) {
        logger.error("Malformed URL exception " + mue+ " occured while accessing the URL ");
    } catch (IOException ioe) {
        logger.error("IO exception " + ioe+ " occured while accessing the URL ");
    } finally {
        if (bufferedReader != null)
            bufferedReader.close();
    }
}

工作正常的代码：

public static void getInfoFromURL() throws IOException {
    Gson gson = null;
    URL url = null;
    BufferedReader bufferedReader = null;
    HttpURLConnection connection =null;
    String inputLine = "";
    try {
        gson = new Gson();
        url = new URL(addressURL);          
                connection = (HttpURLConnection) url.openConnection(); //This seems to be helping
        connection.connect();
        bufferedReader = new BufferedReader(new InputStreamReader(url.openStream()));
        while ((inputLine = bufferedReader.readLine()) != null) {
            addressData = ((AddressData) gson.fromJson(inputLine,AddressData.class));               
        }                   

    } catch (MalformedURLException mue) {
        logger.error("Malformed URL exception " + mue+ " occured while accessing the URL ");
    } catch (IOException ioe) {
        logger.error("IO exception " + ioe+ " occured while accessing the URL ");
    } finally {
        if (bufferedReader != null)
            bufferedReader.close();
    }
}
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