java - 我正在获取HttpResponse，但是responce.getEntity()。getContent()显示NullPointerException

protected String doInBackground(String... urls) {
    String url = urls[0];
    String result = "";

    HttpResponse response = doResponse(url);

    if (response == null) {
        return result;
    } else {

        try {
            result = inputStreamToString(response.getEntity().getContent());

        } catch (IllegalStateException e) {
            Log.e(TAG, e.getLocalizedMessage(), e);

        } catch (IOException e) {
            Log.e(TAG, e.getLocalizedMessage(), e);
        }

    }

    return result;
}

我要在下面将数据发布到数据库中，并附上我剩余的代码，因此请检查并清除我的问题

private HttpResponse doResponse(String url) {

    HttpClient httpclient = new DefaultHttpClient(getHttpParams());

    HttpResponse response = null;

    try {
        switch (taskType) {

        case POST_TASK:
            HttpPost httppost = new HttpPost(url);
            // Add parameters
            httppost.setEntity(new UrlEncodedFormEntity(params));
            response = httpclient.execute(httppost);

            break;
        case GET_TASK:
            HttpGet httpget = new HttpGet(url);
            response = httpclient.execute(httpget);
            break;
        }
    } catch (Exception e) {

        Log.e(TAG, e.getLocalizedMessage(), e);

    }

    return response;
}

private String inputStreamToString(InputStream is) {

    String line = "";
    StringBuilder total = new StringBuilder();

    // Wrap a BufferedReader around the InputStream
    BufferedReader rd = new BufferedReader(new InputStreamReader(is));

    try {
        // Read response until the end
        while ((line = rd.readLine()) != null) {
            total.append(line);
        }
    } catch (IOException e) {
        Log.e(TAG, e.getLocalizedMessage(), e);
    }

    // Return full string
    return total.toString();
}

我在下一行得到NullPointerException，

result = inputStreamToString(response.getEntity().getContent());。

我不了解实体和内容。有人可以帮助我吗？

最佳答案

您的HTTP响应没有实体。这就是getEntity()返回null的原因。

getEntity()的JavaDoc指出可以返回null值。因此，您应该始终进行检查。

例如，代替：

result = inputStreamToString(response.getEntity().getContent());

你可以这样做：

final HttpEntity entity = response.getEntity();
if (entity == null) {
    Log.w(TAG, "The response has no entity.");

    //  NOTE: this method will return "" in this case, so we must check for that in onPostExecute().

    // Do whatever is necessary here...
} else {
    result = inputStreamToString(entity.getContent());
}