Duplicate properties with upper-case field name and JsonProperty annotation

Duplicate properties with upper-case field name and JsonProperty annotation

• Jackson version: 2.8.8
• TestCase

public class JacksonTest {
    public static void main(String[] args) {

        ObjectMapper  objectMapper = new ObjectMapper();
        Person person = new Person("neal", 30);

        try {
            objectMapper.writerWithDefaultPrettyPrinter().writeValue(System.out, person);
            //new ByteArrayInputStream(objectMapper.writeValueAsBytes(person));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static class Person {

        Person(String name, int age) {
            this.Name = name;
            this.Age = age;
        }

        public String getName() {
            return Name;
        }

        public void setName(String name) {
            Name = name;
        }

        public int getAge() {
            return Age;
        }

        public void setAge(int age) {
            Age = age;
        }

        @JsonProperty("Name")
        private String Name;

        @JsonProperty("Age")
        private int Age;

    }
}

• Output:

{
  "name" : "neal",
  "age" : 30,
  "Name" : "neal",
  "Age" : 30
}

Expected:

{
  "Name" : "neal",
  "Age" : 30
}

• Suspect cause: com.fasterxml.jackson.databind.ser.BeanSerializerFactory:138

Neal

[cowtowncoder]

It works because all accessors initially match: “getAge()”, “setAge()” and “age” infer age; and renaming of one renames them all as Age. Same for “name”. Introspection always starts by checking inferred name: getters and setters use bean naming convention, field names used as is. Accessors with same inferred name are grouped into one logical property candidate. After this, annotations are checked and apply to candidates, as a group.

[cowtowncoder]

Not a bug but results from incompatible field/getter/setter naming – fields would imply properties Name and Age (no annotation needed), but setters would imply properties name and age. Those will not automatically match (there is no assumption of case unification), so you end up with twice the properties you expect.

Fortunately there is a simple fix: just move annotations to either setters or getters (either one is fine): this will allow otherwise separate fields and getter/setter pairs to match