序列化：忽略一个元素包含空值的列表属性

Question

I'm working on a java play framework 2.6 web application with mongoDB. Let's consider this model structure:

public class Beneficiary {  
    private Type type; // enum: NGO, PUBLIC_ADMINISTRATION ..
    private Company company;
} 
public class Company {
    private String name;
    private String registrationNumber;
    private List<Person> agent;
}
public class Person {
    private String name;
    private String email;
    private String phoneNumber;
}

I receive this data from a form:

{
  "type" : "NGO",
  "company" : {
    "name" : "ngo name",
    "registrationNumber" : "2233",
    "agent" : [
      {
        "name" : "",
        "email" : "",
        "phoneNumber" : ""
      }
    ]
  }
}

I don't want to store in the database the field agent in this form. I want to ignore it completely if all the fields of the element are empty strings.

I tried annotating with @JsonInclude(JsonInclude.Include.NON_EMPTY) classes and/or fields but this only worked for the field type in the Beneficiary class.

Is there a way to do this without writing a custom annotation?

Thanks

Answer 1

Which JSON serialization library are you using? Jackson or Gson?

Both have support to define your own custom serializers.

You can define a serializer for type Person, and then it will call your code to serialize the JSON when it encounters Person data, you can ignore if all the fields are empty.

For Jackson

public class PersonSerializer extends StdSerializer<Person> {

    public PersonoSerializer() {
        this(null);
    }

    public PersonSerializer(Class<Person> t) {
        super(t);
    }

    @Override
    public void serialize(
      Item value, JsonGenerator jgen, SerializerProvider provider) 
      throws IOException, JsonProcessingException {
        if(value.name.isEmpty() && value.email.isEmpty() && value.phoneNumber.isEmpty()) return;

        jgen.writeStartObject();
        jgen.writeNumberField("id", value.id);
        jgen.writeStringField("itemName", value.itemName);
        jgen.writeNumberField("owner", value.owner.id);
        jgen.writeEndObject();
    }

}

And on your Person class, add this annotation

@JsonSerialize(using = PersonSerializer.class)
Person {
.....
}

Answer 2

There are more options, but I would write some code that checks if those fields are empty strings, and, if so, sets the "agent" to null.

So, assuming you have something like:

saveCompany(Company company) {
   agent=company.getAgent();
   if (StringUtils.isEmpty(agent.getName()) && StringUtils.isEmpty(agent.getEmail()) && StringUtils.isEmpty(agent.getPhoneNumber)) {
        company.setAgent(null);
   }

   saveToMongo(company);
}

If you have many similar cases, you can also write some code that does this through reflection.

if (allFieldsAreEmpty(company.getAgent())) {
       company.setAgent(null);
}

By the way, the data that you should receive from the form should be a bit different,

"agent": [
{
    "name": "",
    "email": "",
    "phoneNumber": ""
}
]

Another options is to set in Play so that when the user enters an empty string in the form, to receive NULL string instead of "". Although you'll still end up with an Agent with all fields set to null.

Answer 3

Used @PreSave annotation provided by Morphia like this

public class Beneficiary {  
    private Type type; // enum: NGO, PUBLIC_ADMINISTRATION ..
    private Company company;
} 
public class Company {
    private String name;
    private String registrationNumber;
    private List<Person> agent;

    @PreSave
    public void preSave(BSONObject dbObj) {
        List<?> agents = (List<?>) dbObj.get("agents");
        for (int i = 0; i < agents.size(); i++) {
            if (Json.toJson(agents.get(i)).size() == 0) {
                agents.remove(i);
            }
        }

        if (agents.size() == 0) {
            dbObj.removeField("agents");
        }
        ....
    }
}
public class Person {
    private String name;
    private String email;
    private String phoneNumber;

    @PreSave
    public void preSave(BSONObject dbObj) {
        if (dbObj.get("name") != null && dbObj.get("name").equals("")) {
            dbObj.removeField("name");
        }
        ....
    }
}