feat: use gson instead of jackson (#25)

Author: jiangmichaellll

pom.xml

@@ -99,20 +99,14 @@
       <artifactId>api-common</artifactId>
     </dependency>
     <dependency>
-      <groupId>com.fasterxml.jackson.core</groupId>
-      <artifactId>jackson-core</artifactId>
-      <version>2.12.1</version>
+      <groupId>com.google.code.gson</groupId>
+      <artifactId>gson</artifactId>
     </dependency>
     <dependency>
       <groupId>com.github.ben-manes.caffeine</groupId>
       <artifactId>caffeine</artifactId>
       <version>2.8.8</version>
     </dependency>
-    <dependency>
-      <groupId>com.fasterxml.jackson.core</groupId>
-      <artifactId>jackson-databind</artifactId>
-      <version>2.12.1</version>
-    </dependency>
     <dependency>
       <groupId>org.scala-lang</groupId>
       <artifactId>scala-library</artifactId>

src/main/java/com/google/cloud/pubsublite/spark/SparkSourceOffset.java

@@ -18,23 +18,21 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 
-import com.fasterxml.jackson.core.JsonProcessingException;
-import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.SerializationFeature;
 import com.google.cloud.pubsublite.Partition;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
-import java.io.IOException;
+import com.google.gson.Gson;
+import com.google.gson.reflect.TypeToken;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.TreeMap;
 import java.util.stream.Collectors;
 
 public final class SparkSourceOffset
     extends org.apache.spark.sql.sources.v2.reader.streaming.Offset {
-  private static final ObjectMapper objectMapper =
-      new ObjectMapper().configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
+  private static final Gson gson = new Gson();
 
   // Using a map to ensure unique partitions.
   private final ImmutableMap<Partition, SparkPartitionOffset> partitionOffsetMap;
@@ -79,26 +77,17 @@ public static SparkSourceOffset merge(SparkPartitionOffset[] offsets) {
     return new SparkSourceOffset(map);
   }
 
-  @SuppressWarnings("unchecked")
   public static SparkSourceOffset fromJson(String json) {
-    Map<String, Number> map;
-    try {
-      // TODO: Use TypeReference instead of Map.class, currently TypeReference breaks spark with
-      // java.lang.LinkageError: loader constraint violation: loader previously initiated loading
-      // for a different type.
-      map = objectMapper.readValue(json, Map.class);
-    } catch (IOException e) {
-      throw new IllegalStateException("Unable to deserialize PslSourceOffset.", e);
-    }
+    Map<Long, Long> map = gson.fromJson(json, new TypeToken<Map<Long, Long>>() {}.getType());
     Map<Partition, SparkPartitionOffset> partitionOffsetMap =
         map.entrySet().stream()
             .collect(
                 Collectors.toMap(
-                    e -> Partition.of(Long.parseLong(e.getKey())),
+                    e -> Partition.of(e.getKey()),
                     e ->
                         SparkPartitionOffset.builder()
-                            .partition(Partition.of(Long.parseLong(e.getKey())))
-                            .offset(e.getValue().longValue())
+                            .partition(Partition.of(e.getKey()))
+                            .offset(e.getValue())
                             .build()));
     return new SparkSourceOffset(partitionOffsetMap);
   }
@@ -109,13 +98,9 @@ public Map<Partition, SparkPartitionOffset> getPartitionOffsetMap() {
 
   @Override
   public String json() {
-    try {
-      Map<Long, Long> map =
-          partitionOffsetMap.entrySet().stream()
-              .collect(Collectors.toMap(e -> e.getKey().value(), e -> e.getValue().offset()));
-      return objectMapper.writeValueAsString(map);
-    } catch (JsonProcessingException e) {
-      throw new IllegalStateException("Unable to serialize PslSourceOffset.", e);
-    }
+    Map<Long, Long> map =
+        partitionOffsetMap.entrySet().stream()
+            .collect(Collectors.toMap(e -> e.getKey().value(), e -> e.getValue().offset()));
+    return gson.toJson(new TreeMap<>(map));
   }
 }