Why InputStream is closed when I use a BuffferedReader?

Question

I get this error when I read an InputStream and try to used it again.

07-20 17:36:24.762  11253-11277/? W/System.err﹕ java.io.IOException
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at java.io.InputStream.reset(InputStream.java:208)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at demo31.com.maps.GMapDirections$DownloadDocumentTask.doInBackground(GMapDirections.java:134)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at demo31.com.maps.GMapDirections$DownloadDocumentTask.doInBackground(GMapDirections.java:86)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:292)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at javautil.concurrent.FutureTask.run(FutureTask.java:237)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
07-20 17:36:24.762  11253-11277/? W/System.err﹕ at java.lang.Thread.run(Thread.java:818)
07-20 17:36:24.762  11253-11277/? D/GMapDirections﹕ Exception while downloading data: java.io.IOException

The code that I'm using is ...

@Override
protected Document doInBackground(ArrayList... latLngs) {
  Log.d(TAG, "DownloadDocumentTask(doInBackground): Estoy dentro del background!!!");
  try {
    HttpsURLConnection urlConnection;
    FileService file = new FileService();
    InputStream iStream;
    Document result;

    file.writeLog(TAG, GMapDirections.class.getName(), getUrlConnection());

    URL url = new URL(getUrlConnection());

    // Creating an http connection to communicate with url
    urlConnection = (HttpsURLConnection) url.openConnection();

    // Connecting to url
    urlConnection.setRequestMethod("POST");
    urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    urlConnection.setRequestProperty("charset", "utf-8");
    urlConnection.setRequestProperty("Accept", "application/xml");
    urlConnection.setDoOutput(true);
    urlConnection.setDoInput(true);
    urlConnection.setUseCaches(false);
    urlConnection.connect();

    //Return data
    iStream = urlConnection.getInputStream();

    //Display what returns POST request
    BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
    StringBuilder sb = new StringBuilder();

    String line;
    while ((line = br.readLine()) != null) {
      sb.append(line + "\n");
    }
    br.close();
    file.writeLog(GMapDirections.TAG, "doInBackground", sb.toString());

    // Parse the data to a Document Object
    DocumentBuilder builder =  DocumentBuilderFactory.newInstance().newDocumentBuilder();
    result = builder.parse(iStream);
    urlConnection.disconnect();

    return result;
  } catch (Exception e) {
     e.printStackTrace();
     Log.d(TAG, "Exception while downloading data: " + e.toString());
  }
  return null;
}

The exception is launched when I try to parse the content of iStream because previously I have read it using BufferedReader.

DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
result = builder.parse(iStream);

So, how I can read the iStream with the BufferedReader and then used it to parse the content and not get an error?

Answer 1

Your stack trace and code do not seem to match up. From the stack trace it looks like doInBackground is recursively calling itself and then InputStream.reset(). But I can see neither call in your code.

Regarding your actual problem re-reading the stream: Since you apparently already tried (and failed) with InputStream.reset(), the amount of data in that stream is probably too large for that (or you forgot to call InputStream.mark()). The easy way is to create another connection + stream and read that. It does mean that you will actually and inefficiently transfer that data twice from the URL.

More efficient ways to do this:

1. Read the entire contents of the stream into memory / or into a temporary file (depending on size) and then use that as your data source.

2. Use TeeInputStream (https://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/input/TeeInputStream.html) to copy stream data as you go.

Answer 2

If you want to read from a Stream again, you'll have to reset it by calling iStream.reset()

From the InputStream docs: http://developer.android.com/reference/java/io/InputStream.html

public synchronized void reset ()

Added in API level 1

Rests this stream to the last marked location. Throws anIOException if the number of bytes read since the mark has been set is greater than the limit provided to mark, or if no mark has been set.

This implementation always throws an IOException and concrete subclasses should provide the proper implementation.

Throws

IOExceptionif this stream is closed or another IOException occurs.

Answer 3

It's because you call BufferedReader.close(). From the Javadocs,

Closes the stream and releases any system resources associated with it.

I looked at this a while ago because I was worried that a sequence like:

new BufferedReader(new FileReader(...))

would leak a Reader handle for the FileReader. Turns out that the BufferedReader.close also closed the underlying reader as well.

Answer 4

Add finally section where you close all streams. Move declaration of streams outside of your try block, i.e. :

BufferedReader br;
InputStream iStream;
try {
    // your regular code, but remove this line as you'll close later
    // br.close();
} catch (Exception whatever) {
    //...
} finally {
    if (iStream != null) {
        iStream.close(); // TODO you need to catch exception here too
    }
}

Answer 5

According with the answer of @emu (see point 1)

More efficient ways to do this:
1. Read the entire contents of the stream into memory / or into a temporary file (depending on size) and then use that as your data source.

The best solution would be ...

        @Override
    protected Document doInBackground(Void... voids) {
        try {
            HttpsURLConnection urlConnection;
            FileService file = new FileService();
            InputStream iStream;
            Document result;

            file.writeLog(TAG, GMapDirections.class.getName(), getUrlConnection());


            URL url = new URL(getUrlConnection());

            // Creating an http connection to communicate with url
            urlConnection = (HttpsURLConnection) url.openConnection();

            // Connecting to url
            urlConnection.setRequestMethod("POST");
            urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            urlConnection.setRequestProperty("charset", "utf-8");
            urlConnection.setRequestProperty("Accept", "application/xml");
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setUseCaches(false);
            urlConnection.connect();

            //Return data
            iStream = urlConnection.getInputStream();

            // Parse the data to a Document Object
            DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            result = builder.parse(iStream);
            urlConnection.disconnect();

            //Write data get it from POST request
            //Transform Document 2 InputStream
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            Source xmlSource = new DOMSource(result);
            Result outputTarget = new StreamResult(outputStream);
            TransformerFactory.newInstance().newTransformer().transform(xmlSource, outputTarget);
            iStream = new ByteArrayInputStream(outputStream.toByteArray());

            //Write document in a file
            BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
            StringBuilder sb = new StringBuilder();

            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line + "\n");
            }
            br.close();
            file.writeLog(GMapDirections.TAG, "doInBackground", sb.toString());

            //Return Document with data
            return result;

        } catch (Exception e) {
            e.printStackTrace();
            Log.d(TAG, "Exception while downloading data: " + e.toString());
        }

        return null;
    }