我正在尝试使用文件流来解析geojson文件,因为该文件可能是一个巨大的文件。 1KB,20MG或1 TB。
我解析所有文件使用流式传输,正如您在ParseGeojsonStream类中看到的那样。
但是当我尝试使用gson解析为json并将其存储在postgressql数据库中时,field属性是一个空对象。
但是我在将其强制转换为json之前做了一个日志,
希望您能理解我。
助焊剂是下一个:
那么,为什么当转换为json以将其存储在数据库中时返回一个空的属性对象?
代码如下:
public class ParseGeojsonStream {
private static List<Feature> features = new ArrayList<Feature>();
public static List<Feature> parseJson(InputStream is) throws IOException {
// Create and configure an ObjectMapper instance
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
// Create a JsonParser instance
try (JsonParser jsonParser = mapper.getFactory().createParser(is)) {
// Check the first token
if (jsonParser.nextToken() != JsonToken.START_OBJECT) {
throw new IllegalStateException("Expected content to be an object");
}
JsonParser featureJson = findFeaturesToken(jsonParser);
if (featureJson == null) {
throw new IOException("Expected content to be not null");
}
if (featureJson.nextToken() != JsonToken.START_ARRAY) {
throw new IOException("Expected content to be an array");
}
// Iterate over the tokens until the end of the array
while (featureJson.nextToken() != JsonToken.END_ARRAY) {
// Read a contact instance using ObjectMapper and do something with it
Feature feature = mapper.readValue(featureJson, Feature.class);
features.add(feature);
}
return features;
}
}
private static JsonParser findFeaturesToken(JsonParser jsonParser) throws IOException {
JsonParser json = jsonParser;
while(json.nextToken() != JsonToken.END_OBJECT) {
String text = json.getText();
if ( text.equalsIgnoreCase(GEOJSONConstants.ApiJSON.FEATURES) ) {
return json;
}
}
return null;
}
}
此存储所有功能,这是一项记录:Feature: Feature(properties={ELEMENTO=null}, geometry={type=MultiPolygon, coordinates=[-3.691344883619331, 40.424004164131894] })
功能分类:
@Data
public class Feature {
private Object properties;
private Object geometry;
}
TableGeojsonStream中的方法:
public String createTable(final String name, final List<Feature> features) {
Gson gson = new Gson();
checkedNameTable= nameTable(name);
jdbcTemplate.execute("CREATE TABLE IF NOT EXISTS " + checkedNameTable + " ( table_id SERIAL, properties jsonb not null, geom geometry(GeometryZ,4326), primary key (table_id));");
for (int i=0; i<1; i++ ) {
Object geometry = features.get(i).getGeometry();
Object property = features.get(i).getProperties();
log.info("property: " + property);
String jsonGeometry = gson.toJson(geometry);
String jsonProperty = gson.toJson(property);
log.info("jsonGeometry: " + jsonGeometry);
log.info("jsonProperty: " + jsonProperty);
String SQL = "INSERT INTO " + checkedNameTable + " ( properties, geom ) VALUES ( '" + property + "', ST_Force3D(ST_SetSRID(ST_GeomFromGeoJSON('" + geometry + "'), 4326) ));";
jdbcTemplate.batchUpdate(SQL);
}
return checkedNameTable;
}
log.info(“属性:” +属性)->显示:property: {ELEMENTO=null}
log.info(“ jsonGeometry:” + jsonGeometry)->显示:jsonGeometry: {"type":"MultiPolygon","coordinates":[-3.691344883619331, 40.424004164131894] }
log.info(“ jsonProperty:” + jsonProperty)->显示:jsonProperty:{}
这是geojson的一部分:
{
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"properties": {
"ELEMENTO": null
},
"geometry": {
"type": "MultiPolygon",
"coordinates": [
[
[
[-3.721150157449075, 40.41560855514652],
[-3.721148651840721, 40.41557793380572],
[-3.721118017962975, 40.41557902578145],
[-3.721113597363736, 40.41549617019551],
[-3.7211442312040024, 40.415495078221284],
[-3.721143913813499, 40.41546535037238],
[-3.72119576233073, 40.41546412605902],
[-3.721195464155001, 40.41543619989809],
[-3.7213085995073105, 40.415434593222656],
[-3.7213088881096974, 40.41546161853896],
[-3.721313602485271, 40.415461589126885],
[-3.7213206932891425, 40.41546334669616],
[-3.721326615119707, 40.415466012462055],
[-3.7213313679771427, 40.41546958642474],
[-3.7213372994291647, 40.41547315303393],
[-3.721340883314031, 40.41547763519334],
[-3.7213444671993554, 40.41548211735267],
[-3.721346882111449, 40.415487507709095],
[-3.7213975616676365, 40.415487191502386],
[-3.721400871367978, 40.41557636033541],
[-3.7213490227697066, 40.41557758474146],
[-3.7213478922770142, 40.415582096314125],
[-3.721345583188133, 40.415586615240166],
[-3.721343274098946, 40.415591134166164],
[-3.7213397767926453, 40.415594759601625],
[-3.7213351008897226, 40.415598392390244],
[-3.721330415365877, 40.415601124334835],
[-3.7213245416249427, 40.41560296278854],
[-3.7213186678836525, 40.41560480124199],
[-3.721316310690866, 40.415604815948214],
[-3.7213165896778255, 40.41563094041987],
[-3.7211999566810587, 40.41563617253719],
[-3.7211996585017926, 40.41560824637715],
[-3.721150157449075, 40.41560855514652]
],
[
[-3.721260835104088, 40.41548714363045],
[-3.7212219511090683, 40.41548828710062],
[-3.7212160966125767, 40.415491927236594],
[-3.721188031570835, 40.41551282309202],
[-3.721190898542824, 40.41556055311452],
[-3.721222980337708, 40.41558467739598],
[-3.7212866245246525, 40.41558428036298],
[-3.7212912908093743, 40.41557974673244],
[-3.7213158296797295, 40.41555977375542],
[-3.72131649840387, 40.41551202167758],
[-3.721282040182673, 40.41548611043945],
[-3.721260835104088, 40.41548714363045]
]
]
]
}
}]
}
答案 0 :(得分:3)
默认情况下,Gson
不会序列化null
的值。自"ELEMENTO": null
起,默认情况下将其排除。这就是输出为空的原因。
要强制对空值进行序列化,请使用以下代码:
GsonBuilder builder = new GsonBuilder();
builder.serializeNulls();
Gson gson = builder.create();
String property = gson.toJson(property);
GsonBuilder
创建一个Gson
,该序列将空值序列化为您想要的值。