Need to parse the JSON ARRAYS that are inside the JSON Object in JAVA

Question

I am trying to parse the JSON data which is present in datas.json.I need to parse the Exclusion datas using Beans/POJO classes.The JSON data is as follows:
"ExclusionList" : { "serviceLevel" : ["sl1","sl2","sl3"], "item" : ["ABC","XYZ"] } }

I've created POJO classes for the ExclusionList but unable to get and print in the console of ECLIPSE IDE.Mypojo class:

List<String> serviceLevel;
List<String> item;
//with gettter and setters.

My main class is as follows:

public static void main(String[] args)
            throws JsonParseException, JsonMappingException, IOException, ParseException, JSONException {
    File jsonFile = new File("C:\\Users\\sameepra\\Videos\\datas.json");
    ObjectMapper mapper = new ObjectMapper();  
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);
    ExclusionList exclusionlist=mapper.readValue(jsonFile,ExclusionList.class);
    List<String> excllist=exclusionlist.getServiceLevel();
    for (int i = 0; i < excllist.size(); i++) {
        System.out.println(excllist.get(i));
    }
}

Getting error as Exception in thread "main" java.lang.NullPointerException

have you initialized List<String> excllist ??

Iamat8
– Iamat8

2019-03-01 06:50:56 +00:00
Commented Mar 1, 2019 at 6:50 — Iamat8
– Iamat8, Commented Mar 1, 2019 at 6:50
Its already inititalized on that provided line as String:

Sameer Prasad
– Sameer Prasad

2019-03-01 06:53:11 +00:00
Commented Mar 1, 2019 at 6:53 — Sameer Prasad
– Sameer Prasad, Commented Mar 1, 2019 at 6:53
String type List*

Sameer Prasad
– Sameer Prasad

2019-03-01 07:03:36 +00:00
Commented Mar 1, 2019 at 7:03 — Sameer Prasad
– Sameer Prasad, Commented Mar 1, 2019 at 7:03
post your console log

Iamat8
– Iamat8

2019-03-01 07:04:10 +00:00
Commented Mar 1, 2019 at 7:04 — Iamat8
– Iamat8, Commented Mar 1, 2019 at 7:04

codiallo · Accepted Answer · 2019-03-01 07:11:40Z

You need to wrap your pojo class in another containing an ExclusionList property.
Try this. The examples below uses lombok for getters , setters and default constructor.


import java.util.List;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

import lombok.Data;

@Data
public class ExclusionListWrapper {

    @JsonProperty("ExclusionList")
    private ExclusionList exclusionList;

    @Data
    class ExclusionList {
        List<String>    serviceLevel;
        List<String>    item;

    }

    public static void main(String[] args) throws Exception {
        String data = "{\"ExclusionList\" : {\"serviceLevel\" : [\"sl1\",\"sl2\",\"sl3\"], \"item\" : [\"ABC\",\"XYZ\"]}}";
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        ExclusionListWrapper exclusionlistWrapper = mapper.readValue(data, ExclusionListWrapper.class);
        List<String> excllist = exclusionlistWrapper.getExclusionList().getServiceLevel();
        for (int i = 0; i < excllist.size(); i++) {
            System.out.println(excllist.get(i));
        }
    }

}

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