Access a list in a json object using java

Question

I have below json string and would like to access the alsoKnownAs list using Java. I am able to getString for the name, I have tried getJSONArray for alsoKnownAs but it doesn't quite workout

{\"name\":\"moses\",\"alsoKnownAs\":[\"njai\", \"njenga\",\"musa\"]}

I can access the name as below but I can't the equivalent of getString method that would return a list of strings or equivalent of getJSONArray for a list of strings

    public static Person parsePersonJson(String json) {

            JSONObject currentPerson;
            String name;

            try {
                currentPerson = new JSONObject(json);

                // so I can access the name like

                name = currentPerson.getString("name");

               //I was trying this to get the list but figure out I was using a list of json objects, so not how to get the list of stings

           JSONArray arrayKnownAs = names.getJSONArray("alsoKnownAs");
                List<String> alsoKnownAs= new ArrayList<>();

                for (int i = 0, l = arrayKnownAs.length(); i < l; i++) {
                    String origin;
                    origin = arrayKnownAs[i];
                    alsoKnownAs.add(origin);
                }



               Person thisPerson =  new Person(

                //I instantiate person object here

                );
                return thisPerson;

            } catch (org.json.JSONException e) {
    // error
            }
            return null;
        }

You could write your own JSON parser. Or you could just use one of the many already existing and battle-tested ones. If you have tried doing so, and had a problem, then post the code you tried, and tell us precisely what the error is. Otherwise, your question boils down to "how to parse JSON in Java", and is a duplicate. — JB Nizet
– JB Nizet, Commented Aug 5, 2018 at 9:16
@JBNizet I have added some clarification and how am approaching it — Moses N. Njenga
– Moses N. Njenga, Commented Aug 5, 2018 at 9:41
stackoverflow.com/questions/45519786/get-json-array-from-php/….. this might help — user3678528
– user3678528, Commented Aug 5, 2018 at 9:50
Thanks @user3678528 for the suggestion, I am okay accessing a list of JSONOjects which I can get by getJSONArray I am trying to get the list of strings in which case if I use getJSONArray I get incompatible types — Moses N. Njenga
– Moses N. Njenga, Commented Aug 5, 2018 at 9:55

Moses N. Njenga · Accepted Answer · 2018-08-06 06:42:07Z

If anyone else is stuck here, It turned out I was on the right track, I can access the List using getJSONArray, but when iterating for each member, I use getString

 public static Person parsePersonJson(String json) {

            JSONObject currentPerson;
            String name;

            try {
                currentPerson = new JSONObject(json);

                // so I can access the name like

                name = currentPerson.getString("name");

                List<String> alsoKnownAs= new ArrayList<>();

                //use getJSONArray to get the list

                JSONArray arrayKnownAs = currentPerson.getJSONArray("alsoKnownAs");

                for (int i = 0, l = arrayKnownAs.length(); i < l; i++) {

                 //This is where I was getting it wrong, i needed to use getString to access list items

                  alsoKnownAs.add(arrayKnownAs.getString(i));
                   }



               Person thisPerson =  new Person(

                //I instantiate person object here

                );
                return thisPerson;

            } catch (org.json.JSONException e) {
             // error
            }
            return null;
        }

Simonluca Landi · Accepted Answer · 2018-08-06 07:01:02Z

Here a solution using com.fasterxml.jackson

Person.java:

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.List;

class Person  {
    final public String name;
    final public List<String> alsoKnownAs;

    @JsonCreator
    public Person(
            @JsonProperty("name") final String name,
            @JsonProperty("alsoKnownAs") final List<String> alsoKnownAs
    ) {
        this.name = name;
        this.alsoKnownAs = alsoKnownAs;
    }

    public static Person parsePersonJson(String json) {
        ObjectMapper objectMapper = new ObjectMapper();
        try {
            return objectMapper.readValue(json, Person.class);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

Here a quick test:

PersonTest.java

import org.junit.Test;

public class PersonTest {


    @Test
    public void parseAJsonToAPerson() {
        String json = "{\"name\":\"moses\",\"alsoKnownAs\":[\"njai\", \"njenga\",\"musa\"]}";
        Person currentPerson = Person.parsePersonJson(json);

        System.out.println("name: " + currentPerson.name);
        System.out.println("alsoKnownAs: " + currentPerson.alsoKnownAs);

    }

}

Test output is:

name: moses
alsoKnownAs: [njai, njenga, musa]

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