Fix GeoJsonReader to handle empty arrays (#600)

Signed-off-by: Martin Davis <mtnclimb@gmail.com>

modules/io/common/src/main/java/org/locationtech/jts/io/geojson/GeoJsonReader.java

@@ -98,32 +98,31 @@ public Geometry read(String json) throws ParseException {
    * @return The resulting JTS Geometry
    * 
    * @throws ParseException
-   *           throws a ParseException if the JSON string cannot be parsed
+   *           throws a ParseException if the JSON string cannot be parsed as a Geometry
    */
+  @SuppressWarnings("unchecked")
   public Geometry read(Reader reader) throws ParseException {
-
-    Geometry result = null;
-
+    Map<String, Object> geometryMap = null;
     JSONParser parser = new JSONParser();
     try {
-      @SuppressWarnings("unchecked")
-      Map<String, Object> geometryMap = (Map<String, Object>) parser
-          .parse(reader);
-
-      GeometryFactory geometryFactory = null;
-      if (this.gf == null) {
-        geometryFactory = this.getGeometryFactory(geometryMap);
-      } else {
-        geometryFactory = this.gf;
-      }
-
-      result = create(geometryMap, geometryFactory);
-
-    } catch (org.json.simple.parser.ParseException e) {
+      Object obj =  parser.parse(reader);
+      geometryMap = (Map<String, Object>) obj;
+    } catch (ClassCastException e) {
+      throw new ParseException("Could not parse Geometry from Json string.");
+    }catch (org.json.simple.parser.ParseException e) {
       throw new ParseException(e);
     } catch (IOException e) {
       throw new ParseException(e);
     }
+
+    GeometryFactory geometryFactory = null;
+    if (this.gf == null) {
+      geometryFactory = this.getGeometryFactory(geometryMap);
+    } else {
+      geometryFactory = this.gf;
+    }
+
+    Geometry result = create(geometryMap, geometryFactory);
 
     return result;
   }

modules/io/common/src/test/java/org/locationtech/jts/io/geojson/GeoJsonReaderTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2020 Martin Davis.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
+ * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ */
+
+package org.locationtech.jts.io.geojson;
+
+import org.locationtech.jts.geom.Geometry;
+import org.locationtech.jts.io.ParseException;
+
+import test.jts.GeometryTestCase;
+
+public class GeoJsonReaderTest extends GeometryTestCase {
+
+  public GeoJsonReader geoJsonRdr;
+
+  public GeoJsonReaderTest(String name) {
+    super(name);
+  }
+
+  @Override
+  public void setUp() throws Exception {
+    this.geoJsonRdr = new GeoJsonReader();
+  }
+
+  public void testEmptyArray() throws ParseException {
+    runParseEx("[]");
+  }
+
+  public void testEmptyObject() throws ParseException {
+    runParseEx("{}");
+  }
+
+  private void runParseEx(String json) {
+    try {
+      Geometry geom = geoJsonRdr.read(json);
+    }
+    catch (ParseException ex) {
+      assertTrue(true);
+    }
+  }
+
+}