Marcel Overdijk Marcel Overdijk - 14 days ago 17
Java Question

JSR-353 How to add null values using javax.json.JsonObjectBuilder

AS the javax.json docs suggest the way to create a JsonObject is using the provided builders like:

JsonBuilderFactory factory = Json.createBuilderFactory(config);
JsonObject value = factory.createObjectBuilder()
.add("firstName", "John")
.add("lastName", "Smith")
.add("age", 25)
.add("address", factory.createObjectBuilder()
.add("streetAddress", "21 2nd Street")
.add("city", "New York")
.add("state", "NY")
.add("postalCode", "10021"))
.add("phoneNumber", factory.createArrayBuilder()
.add(factory.createObjectBuilder()
.add("type", "home")
.add("number", "212 555-1234"))
.add(factory.createObjectBuilder()
.add("type", "fax")
.add("number", "646 555-4567")))
.build();


This example adds values for the gives keys.
In real life the values are probably derived from some (pojo) domain object like:

JsonBuilderFactory factory = Json.createBuilderFactory(config);
JsonObject value = factory.createObjectBuilder()
.add("firstname", customer.getFirstame())
.add("lastname", customer.getLastame())
.add("age", customer.getAge())
....


The JsonOBjectBuilder throw a NPE in case key or value is null. In case the customer has no registered age then above code will throw a NPE.

So basically for every field I add I have to check if the value is null or not and add the actual value and otherwise do not add the field or add JsonValue.NULL for the key.
This causes a lot of (undesired) boilerplate...

In my case I ended up with custom JsonUtils class including various static methods like:

public static void add(JsonObjectBuilder builder, String name, Long value) {
if (value == null) {
builder.add(name, JsonValue.NULL);
}
else {
builder.add(name, value);
}
}

public static void add(JsonObjectBuilder builder, String name, String value) {
if (value == null) {
builder.add(name, JsonValue.NULL);
}
else {
builder.add(name, value);
}
}


and then calling:

builder = Json.createObjectBuilder();
JsonUtils.add(builder, "id", customer.getId());
JsonUtils.add(builder, "name", customer.getName());
JsonUtils.add(builder, "gender", customer.getGender());
builder.build()


But someway if feels not right.
Why does the javax.json provide no easier way to add null values (without if else boilerplate) or am I missing something?

My main point of critism against the JSR-353 api is that despite it looks like a really nice fluent api (see top example from apidoc) but in reality it is not.

Answer

It might be difficult to get your JsonObjectBuilder implementation from the factory but you can make it simpler.

Create a JsonObjectBuilder decorator class that checks for null:

public class NullAwareJsonObjectBuilder implements JsonObjectBuilder {
    // Use the Factory Pattern to create an instance.
    public static JsonObjectBuilder wrap(JsonObjectBuilder builder) {
      if (builder == null) {
        throw new IllegalArgumentException("Can't wrap nothing.");
      }
      return new NullAwareJsonObjectBuilder(builder);
    }

    // Decorated object per Decorator Pattern.
    private final JsonObjectBuilder builder;

    private NullAwareJsonObjectBuilder(JsonObjectBuilder builder) {
      this.builder = builder;
    }

    public JsonObjectBuilder add(String name, JsonValue value) {
      builder.add(name, (value == null) ? JsonValue.NULL : value);
    }

    // Implement all other JsonObjectBuilder methods.
    ..
}

And how you to use it:

JsonObjectBuilder builder = NullAwareJsonObjectBuilder.wrap(
        factory.createObjectBuilder());
builder.add("firstname", customer.getFirstame())
    .add(...
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