我试图从这个网址http://digitalcollections.tcd.ie/home/getMeta.php?pid=MS4418_021获取json对象作为字符串。它不起作用我在downloadUrl函数后得到一个错误。
java.io.IOException: unexpected end of stream on Connection{digitalcollections.tcd.ie:80, proxy=DIRECT@ hostAddress=134.226.115.12 cipherSuite=none protocol=http/1.1} (recycle count=0)
虽然它适用于此androidhive网址http://api.androidhive.info/volley/person_object.json。 我是新的httpconnection下面是我的下载url功能。错误似乎在这一行显示HttpURLConnection conn =（HttpURLConnection）url.openConnection（）;在该行之后的调试器中，conn.getInputStream（）显示IO异常并导致java.io.EOFException：\ n未找到：size = 0 content = ...
// Given a string representation of a URL, sets up a connection and gets
// an input stream.
private InputStream downloadUrl(String urlString) throws IOException {
URL url = new URL(urlString);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(20000 /* milliseconds */);
conn.setConnectTimeout(30000 /* milliseconds */);
conn.setRequestMethod("GET");
//conn.setDoInput(true);
// Starts the query
conn.connect();
InputStream stream = conn.getInputStream();
return stream;
}
其他功能。
// Uses AsyncTask to create a task away from the main UI thread. This task takes a
// URL string and uses it to create an HttpUrlConnection. Once the connection
// has been established, the AsyncTask downloads the contents of the webpage as
// an InputStream. Finally, the InputStream is converted into a string, which is
// displayed in the UI by the AsyncTask's onPostExecute method.
private class DownloadXMLTask extends AsyncTask<String, Void, List<Entry>> {
private String urlFront = "";
@Override
protected List<Entry> doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
try {
return loadJsonFromNetwork(urls[0]);
} catch (IOException e) {
Log.d(TAG, "Unable to retrieve web page. URL may be invalid.");
return null;
} catch (JSONException e) {
Log.d(TAG, "XMLPULLPARSER ERROR IN download json task function");
return null;
}
}
}
// onPostExecute displays the results of the AsyncTask.
@Override
protected void onPostExecute(List<Entry> result) {
//post execution stuff
}
}
加载json和解析器，解析器可能无法正常运行尚未测试。
private List<Entry> loadJsonFromNetwork(String urlString) throws IOException, JSONException {
InputStream stream = null;
int len = 20000; //max amount of characters to display in string
List<Entry> entries = new ArrayList<Entry>();
try {
stream = downloadUrl(urlString); //IOException
String jsonStr = readit(stream,len);
if(jsonStr.equals(null)){
Log.d(TAG, "ERROR json string returned null");
return entries;
}
JSONObject jsonObj = new JSONObject(jsonStr);
//Not sure if the json parser works yet haven't got that far
// Getting JSON Array node
identifier = jsonObj.getJSONArray("identifier");
// looping through All Contacts
for (int i = 0; i < identifier.length(); i++) {
JSONObject c = identifier.getJSONObject(i);
String id = c.getString("type");
if(id.equals("DRIS_FOLDER")) {
String folder = c.getString("$");
entries.add(new Entry(null,null,null,folder));
}
}
// Makes sure that the InputStream is closed after the app is
// finished using it.
//This is where IOexception is called and stream is null
} catch (IOException e) {
Log.d(TAG, "Unable to retrieve json web page. URL may be invalid."+ e.toString());
return entries;
}
finally {
if (stream != null) {
stream.close();
}
}
return entries;
}
我在Nexus_5_API_23仿真器上运行它。
提前致谢。
更新：
在Nexus_5_API_23仿真器上不起作用？虽然它适用于三星GT-ST7500外置手机。希望它适用于模拟器。
答案 0 :(得分：1)
问题是我的计算机上的防病毒/防火墙。它阻止了我的连接，这就是为什么它在外部手机而不是模拟器上工作的原因。我禁用了我的防病毒/防火墙，它工作正常。这里有一个网络限制列表http://developer.android.com/tools/devices/emulator.html#networkinglimitations
答案 1 :(得分：0)
我刚在设备上尝试了该网址，但没有收到任何错误。这是我使用的代码。
返回UI线程的界面
public interface AsyncResponse<T> {
void onResponse(T response);
}
返回String的通用AsyncTask - 可以随意修改它以解析您的JSON并返回List。
public class WebDownloadTask extends AsyncTask<String, Void, String> {
private AsyncResponse<String> callback;
public void setCallback(AsyncResponse<String> callback) {
this.callback = callback;
}
@Override
protected String doInBackground(String... params) {
String url = params[0];
return readFromUrl(url);
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
if (callback != null) {
callback.onResponse(s);
} else {
Log.w(WebDownloadTask.class.getSimpleName(), "The response was ignored");
}
}
private String streamToString(InputStream is) throws IOException {
StringBuilder sb = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
String line;
while ((line = rd.readLine()) != null) {
sb.append(line);
}
return sb.toString();
}
private String readFromUrl(String myWebpage) {
String response = null;
HttpURLConnection urlConnection = null;
try {
URL url = new URL(myWebpage);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
if (inputStream != null) {
response = streamToString(inputStream);
inputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}
return response;
}
}
调用AsyncTask的Activity部分。
String url = "http://digitalcollections.tcd.ie/home/getMeta.php?pid=MS4418_021";
WebDownloadTask task = new WebDownloadTask();
task.setCallback(new AsyncResponse<String>() {
@Override
public void onResponse(String response) {
Toast.makeText(getApplicationContext(), response, Toast.LENGTH_SHORT).show();
}
});
task.execute(url);
答案 2 :(得分：0)
请确保使用 https 而不是 http 来避免Android模拟器上出现此类错误。
private static final String BASE_URL = "https://content.guardianapis.com/search?";