How to read multiple JSON files and write it to a single JSON file using java

Question

I have multiple JSON file like below and want to merge the files and store the data from it into a new single json file as mentione below:

JSON1:

{
    "jobRunID" : "1940",
    "mappingResult": [

        {
            "studyID": "ca209-030",
            "fileName": "aesae.csv",
            "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/aesae.csv",
            "columnName": "ae_start_dt",
            "currentMapping": "ae_start_dt,ae_st_dt",
            "isMapped": "N",
            "timeStamp": "20180827093033"
        },
        {
            "studyID": "ca209-004",
            "fileName": "labressae.csv",
            "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/labressae.csv",
            "columnName": "ae_verbatim",
            "currentMapping": "ae_vtm,ae_vt",
            "isMapped": "N",
            "timeStamp": "20180827093033"
        }

    ]
}

JSON2:

{
    "jobRunID" : "1940",
    "mappingResult": [

        {
            "studyID": "ca209-030",
            "fileName": "aesae.csv",
            "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/aesae.csv",
            "columnName": "ae_start_dt",
            "currentMapping": "ae_start_dt,ae_st_dt",
            "isMapped": "N",
            "timeStamp": "20180827093033"
        },
        {
            "studyID": "ca209-004",
            "fileName": "labressae.csv",
            "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/labressae.csv",
            "columnName": "ae_verbatim",
            "currentMapping": "ae_vtm,ae_vt",
            "isMapped": "N",
            "timeStamp": "20180827093033"
        }

    ]
}

Expected O/P:

{
  "jobRunID": "1940",
  "mappingResult": [
    {
      "studyID": "ca209-030",
      "fileName": "aesae.csv",
      "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/aesae.csv",
      "columnName": "ae_start_dt",
      "currentMapping": "ae_start_dt,ae_st_dt",
      "isMapped": "N",
      "timeStamp": "20180827093033"
    },
    {
      "studyID": "ca209-004",
      "fileName": "labressae.csv",
      "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/labressae.csv",
      "columnName": "ae_verbatim",
      "currentMapping": "ae_vtm,ae_vt",
      "isMapped": "N",
      "timeStamp": "20180827093033"
    },
    {
      "studyID": "ca209-030",
      "fileName": "aesae.csv",
      "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/aesae.csv",
      "columnName": "ae_start_dt",
      "currentMapping": "ae_start_dt,ae_st_dt",
      "isMapped": "N",
      "timeStamp": "20180827093033"
    },
    {
      "studyID": "ca209-004",
      "fileName": "labressae.csv",
      "ref2FilePath": "C://stage/pra/cro/ca/209/030/ref2/labressae.csv",
      "columnName": "ae_verbatim",
      "currentMapping": "ae_vtm,ae_vt",
      "isMapped": "N",
      "timeStamp": "20180827093033"
    }
  ]
}

Any help will be appreciated as i am new handling JSON files in JAVA. As per the above JOSNs for all the same JobID i want to merge the mappingResult from both the files in one o/p file as explained above in expected o/p.

I am trying with java by using below code but it read well for 2 input files but not sure how to di for multiple json file :

public class MergeJSON {
    @JsonMerge
    List<Integer> contacts;

    public List<Integer> getContacts() {
        return contacts;
    }

    public void setContacts(List<Integer> contacts) {
        this.contacts = contacts;
    }

    @Override
    public String toString() {
        return contacts.toString();
    }
    public static void main(String[] args) throws JsonProcessingException, IOException {
        TypeReference<Map<String, MergeJSON>> type = new TypeReference<Map<String, MergeJSON>>() {};
        InputStream input = new ClassPathResource("C:\\Users\\sweta.h.sharma\\Test.json").getInputStream();
        InputStream input2 = new ClassPathResource("C:\\Users\\sweta.h.sharma\\Test1.json").getInputStream();
        ObjectMapper mapper = new ObjectMapper();
        Object contacts = mapper.readValue(input, type);
        mapper.reader(type)
                .withValueToUpdate(contacts)
                .readValues(input2);

            System.out.println(contacts);

}
}

Hi, this question will be downvoted because you haven't included any details of your attempt to solve it - see stackoverflow.com/help/how-to-ask — joel
– joel, Commented Aug 29, 2018 at 10:43

user3468272 · Accepted Answer · 2018-08-29 12:21:51Z

1

Use Jackson Api.
Create Pojo class same as your json object (Class should have members like 'jobRunID','mappingResult').

//class JsonObj with getters & setters 
String jobRunID;
List<Mappingresult> mappingResult;  // Mappingresult is again POJO class with members like studyID,fileName etc

This are classes you have to use

com.fasterxml.jackson.core.JsonFactory;
com.fasterxml.jackson.core.JsonParser;
com.fasterxml.jackson.databind.ObjectMapper;

And Code.

ObjectMapper objMapper=new ObjectMapper();
JsonFactory jfactory = new JsonFactory();
JsonParser jParser1=jfactory.createJsonParser(jsonString1); //json String 1
JsonParser jParser2=jfactory.createJsonParser(jsonString2); //json String 2

JsonObj obj1=objMapper.readValue(jParser1,JsonObj.class);// JsonObj is Pojo for your jsonObject
JsonObj obj2=objMapper.readValue(jParser2,JsonObj.class);

obj1 and obj2 will have list mappingResult as list. You can merge those list into one list and then can write in file or print on console

EDIT :

To get back the result as String, you can use ObjectMapper::writeValueAsString

obj1.getMappingResult().putAll(obj2.getMappingResult());
String jsonString = objMapper.writeValueAsString(obj1);

edited Aug 29, 2018 at 12:21

user3468272

655 bronze badges

answered Aug 29, 2018 at 11:14

Tarun

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2 Comments

Shweta Sharma Over a year ago

What is jsonString1 and jsonString2 ? Also if there are n no. of json file how it will work ?

Tarun Over a year ago

@ShwetaSharma jsonString is Your Json text in form of String which you are reading from "C:\\Users\\sweta.h.sharma\\Test.json"

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