Question

问题在于：

public static <T> T execute(String query, Function<List<JsonNode>, T> function) {
        String jsonString = HttpRequest.get("http://overpass-api.de/api/interpreter", true, "data", query).body();

        List<JsonNode> list = toJsonNodeList(jsonString);

        T res = function.apply(list);

        return res;
    }

此方法：

执行返回json字符串的查询
将该字符串转换为JsonNode列表
最后，将每个JsonNode转换为特定对象

这是将每个JsonNode转换为geojson几何体并返回geojson结果集的函数示例：

public class GeojsonMapper implements Function<List<JsonNode>, GeojsonSingleListResultSet> {

    @Override
    public GeojsonSingleListResultSet apply(List<JsonNode> list) {
        List<Element> elementList = list.parallelStream()
                .map(jsonNode -> {
                    String id = jsonNode.get("id").asText();
                    JsonNode tags = jsonNode.get("tags");
                    switch (jsonNode.get("type").asText()) {
                        case "node":
                            return new Point(jsonNode.get("lat").asDouble(), jsonNode.get("lon").asDouble(), id, tags);
                        case "way":
                            ArrayList<Point> points = new ArrayList<>();
                            JsonNode nodeList = jsonNode.get("geometry");
                            for (int j = 0; j < nodeList.size(); j++) {
                                JsonNode wayNode = nodeList.get(j);
                                points.add(j, new Point(wayNode.get("lat").asDouble(), wayNode.get("lon").asDouble()));
                            }
                            if (Polygon.isPolygon(points, tags)) {
                                return new Polygon(points, id, tags);
                            } else {
                                return new LineString(points, id, tags);
                            }
                        default:
                            Iterator<JsonNode> iterator = jsonNode.get("members").getElements();
                            List<List<Point>> rings = new ArrayList<>();
                            List<Point> ring = null;
                            while (iterator.hasNext()) {
                                JsonNode member = iterator.next();
                                JsonNode geometry = member.get("geometry");
                                ring = new ArrayList<>();
                                for (int ringIndex = 0; ringIndex < geometry.size(); ringIndex++) {
                                    JsonNode coordinates = geometry.get(ringIndex);
                                    ring.add(new Point(coordinates.get("lat").asDouble(), coordinates.get("lon").asDouble()));
                                }
                                rings.add(ring);
                            }
                            return new Multipolygon(Polygon.buildPolygons(rings), id, tags);
                    }
                })
                .collect(toList());

        return new GeojsonSingleListResultSet(elementList);
    }
}

一切都运行良好，但与使用Stream的方法function.apply（）相比，toJsonNodeList（）方法非常慢。这是toJsonNodeList（）的代码：

private static List<JsonNode> toJsonNodeList(String s){

        ObjectMapper mapper = new ObjectMapper();
        List<JsonNode> list = new ArrayList<>();
        try{
        JsonNode resultSet = mapper.readTree(s).get("elements");
            Iterator<JsonNode> iterator = resultSet.getElements();
            while (iterator.hasNext()) {
                list.add(iterator.next());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return list;
    }

有没有办法使用parallelStream解析json字符串，以便提取每个元素并将其转换为JsonNode？

Java使用Stream API解析String

0 个答案: