通過Java SDK向HBase Ganos匯入時空資料-ApsaraDB for HBase版-阿里雲

本文介紹HBase Ganos時空引擎功能如何通過API匯入資料。

構建SimpleFeature

HBase Ganos通過SimpleFeature類表示空間要素。每個SimpleFeature由ID，Geometry對象與其他屬性構成，GeoTools API提供了SimpleFeatureBuilder類協助使用者建立SimpleFeature對象。

SimpleFeatureType sft = ....;
SimpleFeatureBuilder sfBuilder = new SimpleFeatureBuilder(sft);
builder.set("屬性名稱", 屬性值);
 ...
builder.set("geom", Geometry);
SimpleFeature feature = builder.buildFeature(object_id + "_" + date.getTime());

說明構建SimpleFeature時，Ganos會預設產生128位的UUID作為Feature ID。為了節省儲存空間，使用者可以自己指定ID，具體方式可使用以下語句。

SimpleFeature feature =...
feature.getUserData().put(Hints.USE_PROVIDED_FID, java.lang.Boolean.TRUE);

建立Geometry對象

每個SimpleFeature包含一個Geometry對象用來表示要素的空間對象。Geometry的各個空間實體物件定義具體請參見空間對象說明。

GeoTools API提供了GeometryFactory工具類協助使用者建立Geometry對象，具體方法如下：

點要素

通過Coordinate對象建立Geometry。

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
Coordinate coord = new Coordinate(1, 1);
Point point = geometryFactory.createPoint(coord);

通過WKT語言建立Geometry。Well-known text（簡稱WKT）是一種文本標記語言，用於表示向量空間對象、空間參照系統及空間參照系統之間的轉換。
```
 GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
 WKTReader reader = new WKTReader(geometryFactory);
 Point point = (Point) reader.read("POINT (1 1)");
```

線要素

通過Coordinate對象建立Geometry。

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
Coordinate[] coords  =
 new Coordinate[] {new Coordinate(0, 2), new Coordinate(2, 0), new Coordinate(8, 6) };
LineString line = geometryFactory.createLineString(coordinates);

通過WKT語言建立Geometry。

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
WKTReader reader = new WKTReader( geometryFactory );
LineString line = (LineString) reader.read("LINESTRING(0 2, 2 0, 8 6)");

面要素

通過Coordinate對象建立Geometry。

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
Coordinate[] coords  =
   new Coordinate[] {new Coordinate(4, 0), new Coordinate(2, 2),
                     new Coordinate(4, 4), new Coordinate(6, 2), new Coordinate(4, 0) };
LinearRing ring = geometryFactory.createLinearRing( coords );
LinearRing holes[] = null; // use LinearRing[] to represent holes
Polygon polygon = geometryFactory.createPolygon(ring, holes );

通過WKT語言建立Geometry。

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory( null );
WKTReader reader = new WKTReader( geometryFactory );
Polygon polygon = (Polygon) reader.read("POLYGON((20 10, 30 0, 40 10, 30 20, 20 10))");

資料入庫

HBase Ganos通過GeoTools API中的SimpleFeatureWriter寫入資料，SimpleFeatureWriter支援事務，可以通過DataStore的getFeatureWriterAppend方法擷取。

插入單個SimpleFeature。

SimpleFeatureType sft = ....;
SimpleFeatureWriter writer=(SimpleFeatureWriter)ds.getFeatureWriterAppend(sft.getTypeName(), Transaction.AUTO_COMMIT);
SimpleFeature toWrite=writer.next();
toWrite.setAttributes(feature.getAttributes());
toWrite.getUserData().putAll(feature.getUserData());
writer.write();
writer.close();

批量插入SimpleFeature。

HBase Ganos支援批量插入SimpleFeature，通過GeoTools API中的SimpleFeatureStore類實現。

List<SimpleFeature> features=...
SimpleFeatureStore featureStore = (SimpleFeatureStore) ds.getFeatureSource(sft.getTypeName());
List<FeatureId> featureIds = featureStore.addFeatures(new ListFeatureCollection(sft,features));