add geoson tile source

- based on a patch sent by: Yang (apachemaven)
- use jackson-core for stream parsing
- rewrite tags, this way one can use the same the for different data

vtm-extras/src/org/oscim/tiling/source/geojson/GeoJsonTileSource.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2014 Hannes Janetzek
+ *
+ * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
+ *
+ * This program is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.oscim.tiling.source.geojson;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.oscim.core.MapElement;
+import org.oscim.core.Tag;
+import org.oscim.tiling.ITileDataSource;
+import org.oscim.tiling.source.LwHttp;
+import org.oscim.tiling.source.UrlTileDataSource;
+import org.oscim.tiling.source.UrlTileSource;
+
+public abstract class GeoJsonTileSource extends UrlTileSource {
+
+	public GeoJsonTileSource(String url) {
+		super(url);
+		setExtension(".json");
+	}
+
+	@Override
+	public ITileDataSource getDataSource() {
+		Map<String, String> opt = new HashMap<String, String>();
+		opt.put("Accept-Encoding", "gzip");
+		return new UrlTileDataSource(this, new GeoJsonTileDecoder(this), new LwHttp(getUrl(), opt));
+	}
+
+	public Tag getFeatureTag() {
+		return null;
+	}
+
+	/** allow overriding tag handling */
+	public abstract void decodeTags(MapElement mapElement, Map<String, Object> properties);
+
+	public Tag rewriteTag(String key, Object value) {
+
+		if (value == null)
+			return null;
+
+		String val = (value instanceof String) ? (String) value : String.valueOf(value);
+
+		return new Tag(key, val);
+	}
+
+	/** modify mapElement before process() */
+	public void postGeomHook(MapElement mapElement) {
+
+	}
+}