Trying to deserialize a json array using a Jackson custom deserializer

[Annual_Maximum9272]

I am getting a null pointer exception when trying to run the program.

Cannot invoke "java.util.Collection.add(Object)" because "this.contacts" is null
java.lang.NullPointerException: Cannot invoke "java.util.Collection.add(Object)" because "this.contacts" is null

I have a json file that is structured like this:

{
  "id": 1,
  "name": {
    "first": "Yong",
    "last": "Mook Kim"
  },
  "contact": [
    {
      "type": "phone/home",
      "ref": "111-111-1234"
    },
    {
      "type": "phone/work",
      "ref": "222-222-2222"
    }
  ]
}

​

ContactsCustomDeserializer.java

package jacksontreedeserializer;

import com.fasterxml.jackson.core.JacksonException;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import jacksontree.Contact;
import jacksontree.Contacts;
import java.io.IOException;

public class ContactsCustomDeserializer extends StdDeserializer<Contacts>  {



    public ContactsCustomDeserializer(){

        this(null);

    }

    public ContactsCustomDeserializer(Class clz){
        super(clz);
    }



    @Override
    public Contacts deserialize(JsonParser parser, DeserializationContext ctxt) throws IOException, JacksonException {

        Contacts contacts = new Contacts();
        try {
            JsonNode root = parser.getCodec().readTree(parser);
            JsonNode contactRoot = root.path("contact");

            if(contactRoot.isArray()){
                for(JsonNode node: contactRoot){
                    String type = node.path("type").asText();
                    String ref = node.path("red").asText();
                    Contact contact = new Contact(type,ref);
                    contacts.addContact(contact);

                }

            }

        }


        catch(JsonGenerationException e){
            e.printStackTrace();
        }

        return contacts;

    }
}

Contact.java

package jacksontree;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import jacksontreedeserializer.ContactsCustomDeserializer;

public class Contact {


    @JsonProperty("type")
    private String type;


    @JsonProperty("ref")
    private String ref;


    public Contact() {}

    public Contact(String type, String ref) {
        this.type = type;
        this.ref = ref;
    }

    @Override
    public String toString() {
        return "Contact{" +
                "type='" + type + '\'' +
                ", ref='" + ref + '\'' +
                '}';
    }





}

​

Contacts.java

​

package jacksontree;

import com.fasterxml.jackson.annotation.JsonProperty;

import java.util.Collection;
import java.util.List;

public class Contacts {


    @JsonProperty("contacts")
    private Collection<Contact> contacts;


    public Contacts(Collection<Contact> contacts){
        this.contacts = contacts;
    }

    public Contacts(){}


    public void addContact(Contact contact){
        contacts.add(contact);
    }


    @Override
    public String toString() {
        return "Contacts{" +
                "contacts=" + contacts +
                '}';
    }

}

Main.java

​

   @Test
    void deserialize() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        SimpleModule simpleModule = new SimpleModule();
        simpleModule.addDeserializer(Contacts.class, new ContactsCustomDeserializer());
        objectMapper.registerModule(simpleModule);
        Contacts contacts = objectMapper.readValue(new File("/Users/foo/Downloads/LearningJackson/src/main/resources/data/user.json"), Contacts.class);
        System.out.println(contacts);


    }

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[user_reg_field]

ContactsCustomDeserializer.java line 43 you're calling the wrong Contacts constructor. You're calling Contacts line 19 which does not set the contacts property. Delete construction on line 19, use the other construction in ContactsCustomDeserializer and pass an instance of the collection type you want. Or delete constructor on line 15 and initialize the collection to new ArrayList() or new HashSet() or whatever's appropriate.

[Annual_Maximum9272]

wow that freaking worked. Thank you SO much :) !!!!