Add runtime support for V2 int64 string-encoded fields (#2179)

* Serialize v2 int64's as String

* Fix formatting

Author: mbroshi-stripe

src/main/java/com/stripe/model/StringInt64TypeAdapter.java

@@ -0,0 +1,31 @@
+package com.stripe.model;
+
+import com.google.gson.TypeAdapter;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+
+public class StringInt64TypeAdapter extends TypeAdapter<Long> {
+  /** Serializes Long values as JSON strings and deserializes string-encoded integers. */
+  @Override
+  public void write(JsonWriter out, Long value) throws IOException {
+    if (value == null) {
+      out.nullValue();
+      return;
+    }
+
+    out.value(value.toString());
+  }
+
+  @Override
+  public Long read(JsonReader in) throws IOException {
+    JsonToken token = in.peek();
+    if (token == JsonToken.NULL) {
+      in.nextNull();
+      return null;
+    }
+
+    return Long.valueOf(in.nextString());
+  }
+}

src/test/java/com/stripe/net/ApiRequestParamsConverterTest.java

@@ -5,7 +5,11 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.annotations.JsonAdapter;
 import com.google.gson.annotations.SerializedName;
+import com.stripe.model.StringInt64TypeAdapter;
 import com.stripe.param.common.EmptyParam;
 import java.time.Instant;
 import java.util.Arrays;
@@ -122,6 +126,12 @@ private static class HasInstantParam extends ApiRequestParams {
     public Instant instantParam;
   }
 
+  private static class HasStringInt64Param extends ApiRequestParams {
+    @SerializedName("divide_by")
+    @JsonAdapter(StringInt64TypeAdapter.class)
+    public Long divideBy;
+  }
+
   @Test
   public void testHasExtraParams() {
     ModelHasExtraParams params = new ModelHasExtraParams(ParamCode.ENUM_FOO);
@@ -288,6 +298,28 @@ public void testObjectMaps() {
     assertEquals(objBar.get("hello"), "world");
   }
 
+  @Test
+  public void testToMapWithStringInt64Params() {
+    HasStringInt64Param params = new HasStringInt64Param();
+    params.divideBy = 123L;
+
+    Map<String, Object> paramMap = toMap(params);
+
+    TestCase.assertEquals(1, paramMap.size());
+    TestCase.assertTrue(paramMap.containsKey("divide_by"));
+    TestCase.assertEquals("123", paramMap.get("divide_by"));
+  }
+
+  @Test
+  public void testFromJsonWithStringInt64ResourceField() {
+    Gson gson = new GsonBuilder().create();
+
+    HasStringInt64Param resource =
+        gson.fromJson("{\"divide_by\":\"123\"}", HasStringInt64Param.class);
+
+    TestCase.assertEquals(Long.valueOf(123L), resource.divideBy);
+  }
+
   @Test
   public void testToMapWithInstantParams() {
     HasInstantParam params = new HasInstantParam();