Elye Elye - 2 months ago 9
JSON Question

Can I apply a custom deserializer to within another custom deserializer for GSON

The below is a working code that helps to convert JSON in Object accordingly. If the String is

nil
, it will be treated as null.

There's 2 custom deserializer i.e.
MyOwnStringDeserializer
and
MyOwnListDeserializer
. I am not happy with
MyOwnListDeserializer
deserializer, as essentially what it is doing is in term of the String comparison to the rule defined in
MyOwnStringDeserializer
. But I just can't and don't know how to apply the
MyOwnStringDeserializer
into
MyOwnListDeserializer
.

Is there a way for me to do so, that simplify the
MyOwnListDeserializer
? Or even better if there's a way to use just a single custom deserializer and could still achieve the same result?

@Test
public void myTestFunction() {
String myJson1 = "{\"item1\":\"nil\",\"item2\":\"nil\",\"subItemList\":[{\"subItem1\":\"nil\",\"subItem2\":\"nil\"}]}";
String myJson2 = "{\"subItemList\":[]}";

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(new TypeToken<List<MySubItems>>(){ }.getType(), new MyOwnListDeserializer());
gsonBuilder.registerTypeAdapter(String.class, new MyOwnStringDeserializer());
Gson gson = gsonBuilder.create();

MySimpleObject myObj1 = gson.fromJson(myJson1, MySimpleObject.class);
MySimpleObject myObj2 = gson.fromJson(myJson2, MySimpleObject.class);

assertThat(myObj1.equals((myObj2))).isTrue();
}

class MySimpleObject implements Serializable {
String item1 = null;
String item2 = null;
List<MySubItems> subItemList;

@Override
public int hashCode() {
int hash = 17;
hash = 31*hash + ((item1 == null)? 0 :item1.hashCode());
hash = 31*hash + ((item2 == null)? 0 :item2.hashCode());
return hash;
}

@Override
public boolean equals(Object obj) {
if (obj instanceof MySimpleObject) {
return this.hashCode() == obj.hashCode();
}
return super.equals(obj);
}
}

class MySubItems implements Serializable {
String subItem1 = null;
String subItem2 = null;

@Override
public int hashCode() {
int hash = 17;
hash = 31*hash + ((subItem1 == null)? 0 :subItem1.hashCode());
hash = 31*hash + ((subItem2 == null)? 0 :subItem2.hashCode());
return hash;
}

@Override
public boolean equals(Object obj) {
if (obj instanceof MySubItems) {
return this.hashCode() == obj.hashCode();
}
return super.equals(obj);
}
}

class MyOwnStringDeserializer implements JsonDeserializer<String> {
@Override
public String deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
return (json.getAsString().equals("nil"))? null : json.getAsString();
}
}

class MyOwnListDeserializer implements JsonDeserializer<List<MySubItems>> {
@Override
public List<MySubItems> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
List<MySubItems> list = new ArrayList<>();

for (JsonElement element : json.getAsJsonArray()) {
JsonObject subObj = element.getAsJsonObject();
MySubItems subItems = new MySubItems();

if (!subObj.get("subItem1").getAsString().equals("nil")) {
subItems.subItem1 = subObj.get("subItem1").getAsString();
}
if (!subObj.get("subItem2").getAsString().equals("nil")) {
subItems.subItem2 = subObj.get("subItem1").getAsString();
}

if (subItems.subItem1 != null || subItems.subItem2 != null) {
list.add(subItems);
}
}

return (list.size() == 0)? null : list;
}
}

Answer

The method you're looking for is JsonDeserializationContext.deserialize(). Per the warning about how to cause an infinite loop, this invokes any relevant custom deserializers you've set up.

I believe replacing the initialization of subItems inside the loop with a one-liner MySubItems subItems = context.deserialize(element, MySubItems.class); will do the trick, leaving only that and the check around list.add(subItems) in the loop body.

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