source: josm/src/org/openstreetmap/josm/io/ObjectListDownloader.java@ 153

package org.openstreetmap.josm.io;

import static org.openstreetmap.josm.tools.I18n.tr;

import java.io.IOException;
import java.io.InputStream;
import java.util.Collection;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.osm.DataSet;
import org.openstreetmap.josm.data.osm.OsmPrimitive;
import org.openstreetmap.josm.data.osm.visitor.MergeVisitor;
import org.openstreetmap.josm.data.osm.visitor.NameVisitor;
import org.xml.sax.SAXException;

public class ObjectListDownloader extends OsmServerReader {

        /**
         * All the objects to download (if not downloading bounding boxes instead)
         */
        private final Collection<OsmPrimitive> toDownload;
        private final DataSet ds = new DataSet();
        private final MergeVisitor merger = new MergeVisitor(ds);

        public ObjectListDownloader(Collection<OsmPrimitive> toDownload) {
                this.toDownload = toDownload;
        }

        public DataSet parse() throws SAXException, IOException {
                Main.pleaseWaitDlg.progress.setMaximum(toDownload.size());
                Main.pleaseWaitDlg.progress.setValue(0);
                try {
                        final NameVisitor namer = new NameVisitor();
                        for (OsmPrimitive osm : toDownload) {
                                osm.visit(namer);
                                download(tr(namer.className), osm.id);
                                if (cancel)
                                        break;
                        }
                        if (!merger.conflicts.isEmpty())
                                throw new RuntimeException(tr("Conflicts in disjunct objects"));
                        return ds;
                } catch (IOException e) {
                        if (cancel)
                                return null;
                        throw e;
                } catch (SAXException e) {
                        throw e;
                } catch (Exception e) {
                        if (cancel)
                                return null;
                        if (e instanceof RuntimeException)
                                throw (RuntimeException)e;
                        throw new RuntimeException(e);
                }
        }

        private void download(String className, long id) throws IOException, SAXException {
                Main.pleaseWaitDlg.currentAction.setText(tr("Downloading {0} {1}", className, id));
                InputStream in = getInputStream(className+"/"+id);
                if (in == null)
                        return;
                DataSet data = OsmReader.parseDataSet(in, null, null);
                Main.pleaseWaitDlg.progress.setValue(Main.pleaseWaitDlg.progress.getValue()+1);
                if (data.allPrimitives().size() > 1)
                        throw new SAXException(tr("Got more than one object when expecting only one."));
                for (OsmPrimitive osm : data.allPrimitives())
                        osm.visit(merger);
        }
}