OutOfMemoryError exception: Java heap space, how to debug...?

Question

I'm getting a java.lang.OutOfMemoryError exception: Java heap space.

I'm parsing a XML file, storing data and outputting a XML file when the parsing is complete.

I'm bit surprised to get such error, because the original XML file is not long at all.

Code: http://d.pr/RSzp File: http://d.pr/PjrE

Answer 1

Short answer to explain why you have an OutOfMemoryError, for every centroid found in the file you loop over the already "registered" centroids to check if it is already known (to add a new one or to update the already registered one). But for every failed comparison you add a new copy of the new centroid. So for every new centroid it add it as many times as there are already centroids in the list then you encounter the first one you added, you update it and you leave the loop...

Here is some refactored code:

public class CentroidGenerator {

    final Map<String, Centroid> centroids = new HashMap<String, Centroid>();

    public Collection<Centroid> getCentroids() {
        return centroids.values();
    }

    public void nextItem(FlickrDoc flickrDoc) {

        final String event = flickrDoc.getEvent();
        final Centroid existingCentroid = centroids.get(event);

        if (existingCentroid != null) {
            existingCentroid.update(flickrDoc);
        } else {
            final Centroid newCentroid = new Centroid(flickrDoc);
            centroids.put(event, newCentroid);
        }
    }


    public static void main(String[] args) throws IOException, SAXException {

        // instantiate Digester and disable XML validation
        [...]


        // now that rules and actions are configured, start the parsing process
        CentroidGenerator abp = (CentroidGenerator) digester.parse(new File("PjrE.data.xml"));

        Writer writer = null;

        try {
            File fileOutput = new File("centroids.xml");
            writer = new BufferedWriter(new FileWriter(fileOutput));
            writeOuput(writer, abp.getCentroids());

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (writer != null) {
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

    private static void writeOuput(Writer writer, Collection<Centroid> centroids) throws IOException {

        writer.append("<?xml version='1.0' encoding='utf-8'?>" + System.getProperty("line.separator"));
        writer.append("<collection>").append(System.getProperty("line.separator"));

        for (Centroid centroid : centroids) {
            writer.append("<doc>" + System.getProperty("line.separator"));

            writer.append("<title>" + System.getProperty("line.separator"));
            writer.append(centroid.getTitle());
            writer.append("</title>" + System.getProperty("line.separator"));

            writer.append("<description>" + System.getProperty("line.separator"));
            writer.append(centroid.getDescription());
            writer.append("</description>" + System.getProperty("line.separator"));

            writer.append("<time>" + System.getProperty("line.separator"));
            writer.append(centroid.getTime());
            writer.append("</time>" + System.getProperty("line.separator"));

            writer.append("<tags>" + System.getProperty("line.separator"));
            writer.append(centroid.getTags());
            writer.append("</tags>" + System.getProperty("line.separator"));

            writer.append("<geo>" + System.getProperty("line.separator"));

            writer.append("<lat>" + System.getProperty("line.separator"));
            writer.append(centroid.getLat());
            writer.append("</lat>" + System.getProperty("line.separator"));

            writer.append("<lng>" + System.getProperty("line.separator"));
            writer.append(centroid.getLng());
            writer.append("</lng>" + System.getProperty("line.separator"));

            writer.append("</geo>" + System.getProperty("line.separator"));

            writer.append("</doc>" + System.getProperty("line.separator"));

        }
        writer.append("</collection>" + System.getProperty("line.separator") + System.getProperty("line.separator"));

    }

    /**
     * JavaBean class that holds properties of each Document entry. It is important that this class be public and
     * static, in order for Digester to be able to instantiate it.
     */
    public static class FlickrDoc {
        private String id;
        private String title;
        private String description;
        private String time;
        private String tags;
        private String latitude;
        private String longitude;
        private String event;

        public void setId(String newId) {
            id = newId;
        }

        public String getId() {
            return id;
        }

        public void setTitle(String newTitle) {
            title = newTitle;
        }

        public String getTitle() {
            return title;
        }

        public void setDescription(String newDescription) {
            description = newDescription;
        }

        public String getDescription() {
            return description;
        }

        public void setTime(String newTime) {
            time = newTime;
        }

        public String getTime() {
            return time;
        }

        public void setTags(String newTags) {
            tags = newTags;
        }

        public String getTags() {
            return tags;
        }

        public void setLatitude(String newLatitude) {
            latitude = newLatitude;
        }

        public String getLatitude() {
            return latitude;
        }

        public void setLongitude(String newLongitude) {
            longitude = newLongitude;
        }

        public String getLongitude() {
            return longitude;
        }

        public void setEvent(String newEvent) {
            event = newEvent;
        }

        public String getEvent() {
            return event;
        }
    }

    public static class Centroid {
        private final String event;
        private String title;
        private String description;

        private String tags;

        private Integer time;
        private int nbTimeValues = 0; // needed to calculate the average later

        private Float latitude;
        private int nbLatitudeValues = 0; // needed to calculate the average later
        private Float longitude;
        private int nbLongitudeValues = 0; // needed to calculate the average later

        public Centroid(FlickrDoc flickrDoc) {
            event = flickrDoc.event;
            title = flickrDoc.title;
            description = flickrDoc.description;
            tags = flickrDoc.tags;
            if (flickrDoc.time != null) {
                time = Integer.valueOf(flickrDoc.time.trim());
                nbTimeValues = 1; // time is the sum of one value
            }            
            if (flickrDoc.latitude != null) {
                latitude = Float.valueOf(flickrDoc.latitude.trim());
                nbLatitudeValues = 1; // latitude is the sum of one value
            }
            if (flickrDoc.longitude != null) {
                longitude = Float.valueOf(flickrDoc.longitude.trim());
                nbLongitudeValues = 1; // longitude is the sum of one value
            }
        }

        public void update(FlickrDoc newData) {
            title = title + " " + newData.title;
            description = description + " " + newData.description;
            tags = tags + " " + newData.tags;
            if (newData.time != null) {
                nbTimeValues++;
                if (time == null) {
                    time = 0;
                }
                time += Integer.valueOf(newData.time.trim());
            }
            if (newData.latitude != null) {
                nbLatitudeValues++;
                if (latitude == null) {
                    latitude = 0F;
                }
                latitude += Float.valueOf(newData.latitude.trim());
            }
            if (newData.longitude != null) {
                nbLongitudeValues++;
                if (longitude == null) {
                    longitude = 0F;
                }
                longitude += Float.valueOf(newData.longitude.trim());
            }
        }

        public String getTitle() {
            return title;
        }

        public String getDescription() {
            return description;
        }

        public String getTime() {
            if (nbTimeValues == 0) {
                return null;
            } else {
                return Integer.toString(time / nbTimeValues);
            }
        }

        public String getTags() {
            return tags;
        }

        public String getLat() {
            if (nbLatitudeValues == 0) {
                return null;
            } else {
                return Float.toString(latitude / nbLatitudeValues);
            }
        }

        public String getLng() {
            if (nbLongitudeValues == 0) {
                return null;
            } else {
                return Float.toString(longitude / nbLongitudeValues);
            }
        }

        public String getEvent() {
            return event;
        }
    }
}