在GeoTools中，如何在单个图层中的所有多边形周围绘制一条线？

import org.geotools.data.collection.ListFeatureCollection;
import org.geotools.feature.simple.SimpleFeatureBuilder;
import org.geotools.feature.simple.SimpleFeatureTypeBuilder;
import org.geotools.geometry.jts.JTSFactoryFinder;
import org.locationtech.jts.geom.*;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;

public class PolygonOutline {
    public static void main(String[] args) throws Exception {
        // 创建一个空的FeatureCollection
        SimpleFeatureTypeBuilder typeBuilder = new SimpleFeatureTypeBuilder();
        typeBuilder.setName("PolygonOutline");
        typeBuilder.setCRS(DefaultGeographicCRS.WGS84);
        typeBuilder.add("geometry", LineString.class);
        SimpleFeatureType featureType = typeBuilder.buildFeatureType();
        ListFeatureCollection featureCollection = new ListFeatureCollection(featureType);

        // 遍历图层的所有要素
        SimpleFeatureIterator featureIterator = layer.features();
        try {
            while (featureIterator.hasNext()) {
                SimpleFeature feature = featureIterator.next();

                // 获取多边形几何对象
                Geometry geometry = (Geometry) feature.getDefaultGeometry();
                if (geometry instanceof Polygon) {
                    Polygon polygon = (Polygon) geometry;

                    // 获取外环的坐标序列
                    Coordinate[] coordinates = polygon.getExteriorRing().getCoordinates();

                    // 创建新的线几何对象
                    GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
                    LineString lineString = geometryFactory.createLineString(coordinates);

                    // 创建新的Feature对象
                    SimpleFeatureBuilder featureBuilder = new SimpleFeatureBuilder(featureType);
                    featureBuilder.add(lineString);
                    SimpleFeature newFeature = featureBuilder.buildFeature(null);

                    // 将新的Feature对象添加到FeatureCollection中
                    featureCollection.add(newFeature);
                }
            }
        } finally {
            featureIterator.close();
        }

        // 可以将FeatureCollection保存到新的图层中，或者将其绘制在地图上
        // ...
    }
}