Use flat data structure to store lists of points

CHANGELOG.md

@@ -4,6 +4,9 @@ Mapbox welcomes participation and contributions from everyone.
 
 ### main
 - Added `DirectionsRefreshResponse#fromJson(Reader)`, a static factory method that deserializes a `DirectionsRefreshResponse` from a `java.io.Reader`.
+- Added `FlattenListOfPoints` to hold a list of points in a more memory-efficient way.
+- Deprecate `LineString#coordinates()` and `Point#coordinates()`. It's encouraged to use the new `flattenCoordinates()` methods.
+
 
 ### v7.9.0 - November 20, 2025
 

services-geojson/src/main/java/com/mapbox/geojson/BaseCoordinatesTypeAdapter.java

@@ -1,22 +1,20 @@
 package com.mapbox.geojson;
 
 import androidx.annotation.Keep;
+import androidx.annotation.NonNull;
 
 import com.google.gson.TypeAdapter;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
-import com.mapbox.geojson.exception.GeoJsonException;
 import com.mapbox.geojson.shifter.CoordinateShifterManager;
 import com.mapbox.geojson.utils.GeoJsonUtils;
 
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
 
 /**
- *  Base class for converting {@code T} instance of coordinates to JSON and
- *  JSON to instance of {@code T}.
+ * Base class for converting {@code T} instance of coordinates to JSON and
+ * JSON to instance of {@code T}.
  *
  * @param <T> Type of coordinates
  * @since 4.6.0
@@ -25,25 +23,19 @@
 abstract class BaseCoordinatesTypeAdapter<T> extends TypeAdapter<T> {
 
 
-  protected void writePoint(JsonWriter out, Point point) throws  IOException {
+  protected void writePoint(JsonWriter out, Point point) throws IOException {
     if (point == null) {
       return;
     }
-    writePointList(out, point.coordinates());
+    writePointList(out, point.flattenCoordinates());
   }
 
   protected Point readPoint(JsonReader in) throws IOException {
-
-    List<Double> coordinates = readPointList(in);
-    if (coordinates != null && coordinates.size() > 1) {
-      return new Point("Point",null, coordinates);
-    }
-
-    throw new GeoJsonException(" Point coordinates should be non-null double array");
+    return new Point("Point", null, readPointList(in));
   }
 
 
-  protected void writePointList(JsonWriter out, List<Double> value) throws IOException {
+  protected void writePointList(JsonWriter out, double[] value) throws IOException {
 
     if (value == null) {
       return;
@@ -52,38 +44,52 @@ protected void writePointList(JsonWriter out, List<Double> value) throws IOExcep
     out.beginArray();
 
     // Unshift coordinates
-    List<Double> unshiftedCoordinates =
-            CoordinateShifterManager.getCoordinateShifter().unshiftPoint(value);
+    double[] unshiftedCoordinates = CoordinateShifterManager.getCoordinateShifter()
+            .unshiftPointArray(value);
 
-    out.value(GeoJsonUtils.trim(unshiftedCoordinates.get(0)));
-    out.value(GeoJsonUtils.trim(unshiftedCoordinates.get(1)));
+    out.value(GeoJsonUtils.trim(unshiftedCoordinates[0]));
+    out.value(GeoJsonUtils.trim(unshiftedCoordinates[1]));
 
     // Includes altitude
-    if (value.size() > 2) {
-      out.value(unshiftedCoordinates.get(2));
+    if (value.length > 2) {
+      out.value(unshiftedCoordinates[2]);
     }
     out.endArray();
   }
 
-  protected List<Double> readPointList(JsonReader in) throws IOException {
-
+  @NonNull
+  protected double[] readPointList(JsonReader in) throws IOException {
     if (in.peek() == JsonToken.NULL) {
       throw new NullPointerException();
     }
 
-    List<Double> coordinates = new ArrayList<Double>(3);
+    double lon;
+    double lat;
+    double altitude;
     in.beginArray();
-    while (in.hasNext()) {
-      coordinates.add(in.nextDouble());
+    if (in.hasNext()) {
+      lon = in.nextDouble();
+    } else {
+      throw new IndexOutOfBoundsException("Point coordinates should contain at least two values");
     }
-    in.endArray();
-
-    if (coordinates.size() > 2) {
-      return CoordinateShifterManager.getCoordinateShifter()
-              .shiftLonLatAlt(coordinates.get(0), coordinates.get(1), coordinates.get(2));
+    if (in.hasNext()) {
+      lat = in.nextDouble();
+    } else {
+      throw new IndexOutOfBoundsException("Point coordinates should contain at least two values");
+    }
+    if (in.hasNext()) {
+      altitude = in.nextDouble();
+      // Consume any extra value but don't store it
+      while (in.hasNext()) {
+        in.skipValue();
+      }
+      in.endArray();
+      return CoordinateShifterManager.getCoordinateShifter().shift(lon, lat, altitude);
+    } else {
+      in.endArray();
+      return CoordinateShifterManager.getCoordinateShifter().shift(lon, lat);
     }
-    return CoordinateShifterManager.getCoordinateShifter()
-            .shiftLonLat(coordinates.get(0), coordinates.get(1));
+
   }
 
 }

services-geojson/src/main/java/com/mapbox/geojson/BaseGeometryTypeAdapter.java

@@ -18,29 +18,68 @@
  *
  * @param <G> Geometry
  * @param <T> Type of coordinates
+ * @param <A> The type of coordinates adapter
  * @since 4.6.0
  */
 @Keep
-abstract class BaseGeometryTypeAdapter<G, T> extends TypeAdapter<G> {
+abstract class BaseGeometryTypeAdapter<G, T, A> extends TypeAdapter<G> {
 
   private volatile TypeAdapter<String> stringAdapter;
   private volatile TypeAdapter<BoundingBox> boundingBoxAdapter;
-  private volatile TypeAdapter<T> coordinatesAdapter;
+  private final BaseCoordinatesTypeAdapter<A> coordinatesAdapter;
 
   private final Gson gson;
 
-  BaseGeometryTypeAdapter(Gson gson, TypeAdapter<T> coordinatesAdapter) {
+  BaseGeometryTypeAdapter(Gson gson, BaseCoordinatesTypeAdapter<A> coordinatesAdapter) {
+    if (coordinatesAdapter == null) {
+      throw new GeoJsonException("Coordinates type adapter is null");
+    }
     this.gson = gson;
     this.coordinatesAdapter = coordinatesAdapter;
     this.boundingBoxAdapter = new BoundingBoxTypeAdapter();
   }
 
-  public void writeCoordinateContainer(JsonWriter jsonWriter, CoordinateContainer<T> object)
+  public void writeFlattenedCoordinateContainer(
+          JsonWriter jsonWriter,
+          FlattenedCoordinateContainer<T, A> object
+  ) throws IOException {
+    if (object == null) {
+      jsonWriter.nullValue();
+      return;
+    }
+    writeCommon(jsonWriter, object);
+    jsonWriter.name("coordinates");
+    coordinatesAdapter.write(jsonWriter, object.flattenCoordinates());
+    jsonWriter.endObject();
+  }
+
+  public void writeCoordinateContainer(JsonWriter jsonWriter, CoordinateContainer<A> object)
           throws IOException {
     if (object == null) {
       jsonWriter.nullValue();
       return;
     }
+
+    writeCommon(jsonWriter, object);
+
+    jsonWriter.name("coordinates");
+    if (object.coordinates() == null) {
+      jsonWriter.nullValue();
+    } else {
+      coordinatesAdapter.write(jsonWriter, object.coordinates());
+    }
+
+    jsonWriter.endObject();
+  }
+
+  /**
+   * Write the common part of the coordinate container: "type" and "bbox".
+   */
+  private void writeCommon(
+          JsonWriter jsonWriter,
+          @SuppressWarnings("rawtypes")
+          CoordinateContainer object
+  ) throws IOException {
     jsonWriter.beginObject();
     jsonWriter.name("type");
     if (object.type() == null) {
@@ -64,17 +103,6 @@ public void writeCoordinateContainer(JsonWriter jsonWriter, CoordinateContainer<
       }
       boundingBoxAdapter.write(jsonWriter, object.bbox());
     }
-    jsonWriter.name("coordinates");
-    if (object.coordinates() == null) {
-      jsonWriter.nullValue();
-    } else {
-      TypeAdapter<T> coordinatesAdapter = this.coordinatesAdapter;
-      if (coordinatesAdapter == null) {
-        throw new GeoJsonException("Coordinates type adapter is null");
-      }
-      coordinatesAdapter.write(jsonWriter, object.coordinates());
-    }
-    jsonWriter.endObject();
   }
 
   public CoordinateContainer<T> readCoordinateContainer(JsonReader jsonReader) throws IOException {
@@ -86,7 +114,7 @@ public CoordinateContainer<T> readCoordinateContainer(JsonReader jsonReader) thr
     jsonReader.beginObject();
     String type = null;
     BoundingBox bbox = null;
-    T coordinates = null;
+    A coordinates = null;
 
     while (jsonReader.hasNext()) {
       String name = jsonReader.nextName();
@@ -114,7 +142,7 @@ public CoordinateContainer<T> readCoordinateContainer(JsonReader jsonReader) thr
           break;
 
         case "coordinates":
-          TypeAdapter<T> coordinatesAdapter = this.coordinatesAdapter;
+          TypeAdapter<A> coordinatesAdapter = this.coordinatesAdapter;
           if (coordinatesAdapter == null) {
             throw new GeoJsonException("Coordinates type adapter is null");
           }
@@ -133,5 +161,5 @@ public CoordinateContainer<T> readCoordinateContainer(JsonReader jsonReader) thr
 
   abstract CoordinateContainer<T> createCoordinateContainer(String type,
                                                             BoundingBox bbox,
-                                                            T coordinates);
+                                                            A coordinates);
 }