Removed Jackson dependency

Signed-off-by: Abhijeet Shukla <abhijeetshuklaoist@gmail.com>

Fixed formatting

google-cloud-firestore/pom.xml

@@ -110,8 +110,8 @@
       <artifactId>gson</artifactId>
     </dependency>
     <dependency>
-      <groupId>com.fasterxml.jackson.core</groupId>
-      <artifactId>jackson-core</artifactId>
+      <groupId>com.google.code.gson</groupId>
+      <artifactId>gson</artifactId>
     </dependency>
     <dependency>
       <groupId>com.google.protobuf</groupId>
@@ -149,11 +149,6 @@
       <version>0.0.13</version>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>com.fasterxml.jackson.core</groupId>
-      <artifactId>jackson-databind</artifactId>
-      <scope>test</scope>
-    </dependency>
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-lang3</artifactId>

google-cloud-firestore/src/test/java/com/google/cloud/firestore/LocalFirestoreHelper.java

@@ -19,8 +19,6 @@
 import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.doAnswer;
 
-import com.fasterxml.jackson.core.type.TypeReference;
-import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
 import com.google.api.gax.retrying.RetrySettings;
@@ -55,13 +53,23 @@
 import com.google.firestore.v1.StructuredQuery.UnaryFilter;
 import com.google.firestore.v1.Value;
 import com.google.firestore.v1.Write;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.internal.LinkedTreeMap;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.google.gson.stream.JsonWriter;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.Empty;
 import com.google.protobuf.GeneratedMessageV3;
 import com.google.protobuf.Message;
 import com.google.protobuf.NullValue;
 import com.google.type.LatLng;
 import java.io.IOException;
+import java.lang.reflect.Type;
 import java.math.BigInteger;
 import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
@@ -970,18 +978,88 @@ public static <T> Map<String, T> mapAnyType(Object... entries) {
   }
 
   private static Map<String, Object> fromJsonString(String json) {
-    try {
-      ObjectMapper mapper = new ObjectMapper();
-      return mapper.readValue(json, new TypeReference<Map<String, Object>>() {});
-    } catch (IOException e) {
-      throw new RuntimeException(e);
-    }
+    Type type = new TypeToken<Map<String, Object>>() {}.getType();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapterFactory(CustomObjectTypeAdapter.FACTORY);
+    Gson gson = gsonBuilder.create();
+    return gson.fromJson(json, type);
   }
 
   public static Map<String, Object> fromSingleQuotedString(String json) {
     return fromJsonString(json.replace("'", "\""));
   }
 
+  static class CustomObjectTypeAdapter extends TypeAdapter<Object> {
+    public static final TypeAdapterFactory FACTORY =
+        new TypeAdapterFactory() {
+          @SuppressWarnings("unchecked")
+          @Override
+          public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+            if (Map.class.isAssignableFrom(type.getRawType())) {
+              return (TypeAdapter<T>) new CustomObjectTypeAdapter();
+            }
+            return null;
+          }
+        };
+
+    private final TypeAdapter<Object> delegate = new Gson().getAdapter(Object.class);
+
+    @Override
+    public Object read(JsonReader in) throws IOException {
+      JsonToken token = in.peek();
+      switch (token) {
+        case BEGIN_ARRAY:
+          List<Object> list = new ArrayList<Object>();
+          in.beginArray();
+          while (in.hasNext()) {
+            list.add(read(in));
+          }
+          in.endArray();
+          return list;
+
+        case BEGIN_OBJECT:
+          Map<String, Object> map = new LinkedTreeMap<String, Object>();
+          in.beginObject();
+          while (in.hasNext()) {
+            map.put(in.nextName(), read(in));
+          }
+          in.endObject();
+          return map;
+
+        case STRING:
+          return in.nextString();
+
+        case NUMBER:
+          String validNumber = in.nextString();
+          try {
+            return Integer.parseInt(validNumber);
+          } catch (NumberFormatException nfe) {
+            try {
+              return Long.parseLong(validNumber);
+            } catch (NumberFormatException nfe2) {
+              return Double.parseDouble(validNumber);
+            }
+          }
+
+        case BOOLEAN:
+          return in.nextBoolean();
+
+        case NULL:
+          in.nextNull();
+          return null;
+
+        default:
+          throw new IllegalStateException();
+      }
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public void write(JsonWriter out, Object value) throws IOException {
+      delegate.write(out, value);
+    }
+  }
+
   public static String fullPath(DocumentReference ref, FirestoreOptions options) {
     return ResourcePath.create(
             DatabaseRootName.of(options.getProjectId(), options.getDatabaseId()),

google-cloud-firestore/src/test/java/com/google/cloud/firestore/MapperTest.java

@@ -1214,7 +1214,7 @@ public void primitiveDeserializeLong() {
   @Test
   public void primitiveDeserializeWrongTypeMap() {
     assertExceptionContains(
-        "Failed to convert value of type java.util.LinkedHashMap to String "
+        "Failed to convert value of type com.google.gson.internal.LinkedTreeMap to String "
             + "(found in field 'value')",
         new Runnable() {
           @Override