Extract coordinates from KML file in Java

Following the javadocs (unofficial) you need to check - using instanceof - each Feature whether is is a Placemark, if yes cast to it and get the Geometry which itself needs to be checked whether it is a Polygon, if yes then cast to it. After that the path to the coordinates is the following (just as it come in the kml-file):

getOuterBoundaryIs > getlinearRing > getCoordinates

Here is how it looks like in code:

@Test
public void parseKml() {
    String src = "misctests/stackoverflow/kml/labasa.kml";
    try(InputStream is = getClass().getClassLoader().getResourceAsStream(src)) {
        Assert.assertNotNull(is);
        Kml kml = Kml.unmarshal(is);
        Feature feature = kml.getFeature();
        parseFeature(feature);
    }
}

private void parseFeature(Feature feature) {
    if(feature != null) {
        if(feature instanceof Document) {
            Document document = (Document) feature;
            List<Feature> featureList = document.getFeature();
            for(Feature documentFeature : featureList) {
                if(documentFeature instanceof Placemark) {
                    Placemark placemark = (Placemark) documentFeature;
                    Geometry geometry = placemark.getGeometry();
                    parseGeometry(geometry);
                }
            }
        }
    }
}

private void parseGeometry(Geometry geometry) {
    if(geometry != null) {
        if(geometry instanceof Polygon) {
            Polygon polygon = (Polygon) geometry;
            Boundary outerBoundaryIs = polygon.getOuterBoundaryIs();
            if(outerBoundaryIs != null) {
                LinearRing linearRing = outerBoundaryIs.getLinearRing();
                if(linearRing != null) {
                    List<Coordinate> coordinates = linearRing.getCoordinates();
                    if(coordinates != null) {
                        for(Coordinate coordinate : coordinates) {
                            parseCoordinate(coordinate);
                        }
                    }
                }
            }
        }
    }
}

private void parseCoordinate(Coordinate coordinate) {
    if(coordinate != null) {
        System.out.println("Longitude: " +  coordinate.getLongitude());
        System.out.println("Latitude : " +  coordinate.getLatitude());
        System.out.println("Altitude : " +  coordinate.getAltitude());
        System.out.println("");
    }
}

With respect to A4L answer , thank you so much while i have added some more extraction methods which will get data from folder and document with point line and polygon extraction with spring MVC using javaapi4kml using package

<dependency>
<groupId>de.micromata.jak</groupId>
<artifactId>JavaAPIforKml</artifactId>
<version>2.2.0</version>
</dependency> 

@RequestMapping(value = "/testKml", method = RequestMethod.POST)
public Map<String, Object> parseKml(@RequestBody Map<String, Object> data){
    Map<String, Object> response = new HashMap<String, Object>();
    List<Map<String, Object>> wktObjrow = new ArrayList<Map<String, Object>>();
    String src = data.get("kmlfile").toString();
    try {
        URL url;
        url = new URL(src);
        URLConnection conn = url.openConnection();
        InputStream is = url.openStream();
        Assert.notNull(is);
        Kml kml = Kml.unmarshal(is);
        Feature feature = kml.getFeature();
        Map<String, Object> geodata = new HashMap<String, Object>();

        if(feature != null) {
            if(feature instanceof Document) {
                Document document = (Document) feature;
                List<Feature> featureList = document.getFeature();
                for(Feature documentFeature : featureList) {
                    if(documentFeature instanceof Placemark) {
                        geodata = new HashMap<String, Object>();
                        Placemark placemark = (Placemark) documentFeature;
                        Geometry geometry = placemark.getGeometry();
                        geodata = parseGeometry(geometry, documentFeature.getName().toString());
                        if(!geodata.isEmpty())
                        {
                            wktObjrow.add(geodata);
                        }
                    }
                    else if(documentFeature instanceof Folder) 
                    {
                        Folder folder = (Folder) documentFeature;
                        List<Feature> folderfeaturList = folder.getFeature();
                        for(Feature folderfeature : folderfeaturList) 
                        {
                            geodata = new HashMap<String, Object>();
                            if(folderfeature instanceof Placemark) {
                                Placemark placemark = (Placemark) folderfeature;
                                Geometry geometry = placemark.getGeometry();
                                //push each of return store in list
                                geodata = parseGeometry(geometry, placemark.getName().toString());
                                if(!geodata.isEmpty())
                                {
                                    wktObjrow.add(geodata);
                                }
                            }
                            else
                            {
                                System.err.println("folderfeatures was not of type Placemark"); 
                            }
                        }
                    }
                    else
                    {
                        System.err.println("Was not instance of Placemark or Folder");
                    }
                }
                System.out.println("wktObjrow : "+wktObjrow);
            }
            else
            {
                System.err.println("instance of feature was Not Document");
                if(feature instanceof Folder) {
                    Folder folder = (Folder) feature;
                    List<Feature> featureList = folder.getFeature();

                    geodata = new HashMap<String, Object>();

                    for(Feature documentFeature : featureList) {

                        if(documentFeature instanceof Placemark) {
                            Placemark placemark = (Placemark) documentFeature;
                            Geometry geometry = placemark.getGeometry();
                            if(documentFeature.getName().toString().length() > 0)
                            {
                                geodata =  parseGeometry(geometry, documentFeature.getName().toString());
                                if(!geodata.isEmpty())
                                {
                                    wktObjrow.add(geodata);
                                }
                            }
                            else 
                            {
                                geodata = parseGeometry(geometry, placemark.getName().toString());
                                if(!geodata.isEmpty())
                                {
                                    wktObjrow.add(geodata);
                                }
                            }

                        }else
                        {
                            System.err.println("Was not instance of Placemark");
                        }
                    }
                    System.out.println("wktObjrow : "+wktObjrow);

                }
            }
        }
        else
        {
            System.err.println("Feature was null");
            response.put("Null", "Feature was null");
        }
    }
    catch (Exception e) {
        // TODO: handle exception
        System.err.println("Exception @ : "+ e);
    }

    if(!wktObjrow.isEmpty() && wktObjrow != null)
    {
        response.put("data", wktObjrow);
    }

    return response;
}

public Map<String, Object> parseGeometry(Geometry geometry,String name) {
    // <Point> <LinearRing> <Geometry> <Model> <LineString> <Polygon> <MultiGeometry>

    Map<String, Object> response = new HashMap<String, Object>();
    List<Map<String, Object>> wktObjrow = new ArrayList<Map<String, Object>>();

    if(geometry != null) {
        if(geometry instanceof Polygon) {
            Polygon polygon = (Polygon) geometry;
            Boundary outerBoundaryIs = polygon.getOuterBoundaryIs();
            if(outerBoundaryIs != null) {
                LinearRing linearRing = outerBoundaryIs.getLinearRing();
                if(linearRing != null) {
                    List<Coordinate> coordinates = linearRing.getCoordinates();
                    if(coordinates != null) {
                        Map<String, Object> map = new HashMap<String, Object>();
                        ArrayList<String> wkt_lonlat = new ArrayList<String>();
                        for(Coordinate coordinate : coordinates) {
                            wkt_lonlat.add(coordinate.getLongitude()+" "+coordinate.getLatitude());
                        }
                        response.put("name",name);
                        response.put("category","POLYGON");
                        response.put("row","POLYGON(("+String.join(",", wkt_lonlat)+"))");
                    }
                    else
                    {
                        System.err.println("coordinate was null");
                    }
                }
            }
        }
        else if(geometry instanceof Point)
        {
            Point point = (Point) geometry;
            List<Coordinate> coordinates = point.getCoordinates();
            if(coordinates != null  && !coordinates.isEmpty())
            {
                if(coordinates != null) {

                    for(Coordinate coordinate : coordinates) {
                        Map<String, Object> map = new HashMap<String, Object>();
                        response.put("lon",coordinate.getLongitude());
                        response.put("lat",coordinate.getLatitude());
                        response.put("name",name);
                        response.put("category","POINT");
                    }
                }
            }
        }
        else if(geometry instanceof LineString)
        {
            LineString line = (LineString) geometry;
            List<Coordinate> coordinates = line.getCoordinates();
            if(coordinates != null  && !coordinates.isEmpty())
            {
                if(coordinates != null) {
                    Map<String, Object> map = new HashMap<String, Object>();
                    ArrayList<String> wkt_lonlat = new ArrayList<String>();
                    for(Coordinate coordinate : coordinates) {
                        wkt_lonlat.add(coordinate.getLongitude()+" "+coordinate.getLatitude());
                    }
                    response.put("name",name);
                    response.put("category","LINESTRING");
                    response.put("row","LINESTRING("+String.join(",", wkt_lonlat)+")");
                }
            }
       }
       else if(geometry instanceof MultiGeometry)
       {

            MultiGeometry multigeometry = (MultiGeometry) geometry;
               for (int j = 0; j < multigeometry.getGeometry().size(); j++) {
                    if(multigeometry.getGeometry().get(j) instanceof LineString)
                    {
                        LineString line = (LineString) multigeometry.getGeometry().get(j);
                        List<Coordinate> coordinates = line.getCoordinates();
                        if(coordinates != null  && !coordinates.isEmpty())
                        {
                            if(coordinates != null) {
                                Map<String, Object> map = new HashMap<String, Object>();

                                ArrayList<String> wkt_lonlat = new ArrayList<String>();

                                for(Coordinate coordinate : coordinates) {
                                    wkt_lonlat.add(coordinate.getLongitude()+" "+coordinate.getLatitude());
                                }
                                response.put("name",name);
                                response.put("category","LINESTRING");
                                response.put("row","LINESTRING("+String.join(",", wkt_lonlat)+")");
                            }
                        }
                    }
                    else if(multigeometry.getGeometry().get(j) instanceof Point)
                    {
                        Point point = (Point) multigeometry.getGeometry().get(j);
                        List<Coordinate> coordinates = point.getCoordinates();
                           if(coordinates != null  && !coordinates.isEmpty())
                           {
                               if(coordinates != null) {
                                   for(Coordinate coordinate : coordinates) {
                                    Map<String, Object> map = new HashMap<String, Object>();
                                    response.put("lon",coordinate.getLongitude());
                                    response.put("lat",coordinate.getLatitude());
                                    response.put("name",name);
                                    response.put("category","POINT");
                                   }
                               }
                           }
                    }
                    else if(multigeometry.getGeometry().get(j) instanceof Polygon)
                    {
                        Polygon polygon = (Polygon) multigeometry.getGeometry().get(j);
                        Boundary outerBoundaryIs = polygon.getOuterBoundaryIs();
                        if(outerBoundaryIs != null) {
                            LinearRing linearRing = outerBoundaryIs.getLinearRing();
                            if(linearRing != null) {
                                List<Coordinate> coordinates = linearRing.getCoordinates();
                                if(coordinates != null) {

                                    Map<String, Object> map = new HashMap<String, Object>();

                                    ArrayList<String> wkt_lonlat = new ArrayList<String>();

                                    for(Coordinate coordinate : coordinates) {
                                        wkt_lonlat.add(coordinate.getLongitude()+" "+coordinate.getLatitude());
                                    }
                                    response.put("name",name);
                                    response.put("category","POLYGON");
                                    response.put("row","POLYGON(("+String.join(",", wkt_lonlat)+"))");
                                }
                                else
                                {
                                    System.err.println("coordinate was null");
                                }
                            }
                        }
                    }
               }

       }
    }
    else
    {
        System.err.println("geometry was null");
        response.put("Null", "geometry was null");
    }
    return response;
}