How to convert the free text into Json String Array in Java using GSON library?

Question

I am having free text available into the file. I am stucked while convert it into the json string array

The columns names are variable and can be n number of columns

email_from,email_to,DATE_CHANGED

[email protected], [email protected], 1447666867

[email protected], [email protected], 1447668867

The first line is of headers, and the rest of all the lines are their values. So, every line would contain, same number of parameters with respect to each column. Columns are comma separated.

The json string response should be looked like this

{
 "data": [
    {
        "email_from": "[email protected]",
        "email_to": "[email protected]",
        "DATE_CHANGED": "1447666867"
    },
    {
        "email_from": "[email protected]",
        "email_to": "[email protected]",
        "DATE_CHANGED": "1447668867"
    }
 ]
}

Answer 1

The following code opens a file with comma-delimited strings and uses while loop to construct JsonObject and then keeps adding them to the JsonArray and finally prints it (Please add your validations as well you could move majority of the code out of try block if you wish to make the code perform better).

It addresses the need for having n number of columns in the file.

package gjson;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;

import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;

public class GJSONTest {
    public static void main(String[] args) {

        // create an array called datasets
        JsonArray datasets = new JsonArray();

        File file = new File("C:\\test_stackoverflow\\list.txt");

        try (BufferedReader br = new BufferedReader(new FileReader(file)))  {
            String line;
            boolean flag = true; 
            List<String> columns = null; 
            while ((line = br.readLine()) != null) {
               if (flag) {
                   flag = false; 
                   //process header 
                   columns = Arrays.asList(line.split(","));
               } else {
                   //to store the object temporarily
                   JsonObject obj = new JsonObject(); 
                   List<String> chunks = Arrays.asList(line.split(","));

                   for(int i = 0; i < columns.size(); i++) {
                       obj.addProperty(columns.get(i), chunks.get(i));
                   }
                   datasets.add(obj); 
               } 
            }
        } catch(FileNotFoundException fnfe) {
            System.out.println("File not found.");
        } catch(IOException io) {
            System.out.println("Cannot read file.");
        }

        Gson gson = new GsonBuilder().setPrettyPrinting().serializeNulls().setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE).create();
        System.out.println(gson.toJson(datasets));
    }
}

See the following screenshots (below with 3 columns)

Added another column to the text file and following is the output.

Here is the sample .txt file containing your data

Answer 2

private String getParsedData(String data){

    String[] lines = data.split("\\r?\\n");

    List<Map> dataList = new ArrayList<Map>();


    int colCount = 0;

    if(lines.length > 1){

        String keyLine = lines[0];

        String[] keys = keyLine.split(",");

        for(int i = 1; i < lines.length; i++){

            colCount = 0;
            Map<String, Object> rawObj = new HashMap<String, Object>();

            try {

                String[] values = lines[i].split(",");

                for(String value: values){

                    rawObj.put(keys[colCount], value);
                    colCount++;
                }   

            } catch (Exception e) {

            }

            dataList.add(rawObj);
        }
    }


    Map<String, Object> rawObj = new HashMap<String, Object>();
    rawObj.put("data", dataList);
    Gson gson = new Gson();

    String res = gson.toJson(rawObj);

    return res;
}

String data = "email_from,email_to,DATE_CHANGED\r\[email protected], [email protected], 1447666867\r\[email protected], [email protected], 1447668867";

But I am not sure whether its an efficient code or not.

Answer 3

Try this code:

public class ContactObject {
    private String emailFrom;
    private String emailTo;
    private String dateChanged;

    public ContactObject(String emailFrom, String emailTo, String dateChanged) {
        this.emailFrom = emailFrom;
        this.emailTo = emailTo;
        this.dateChanged = dateChanged;
    }

    @Override
    public String toString() {
        return "{email_from:" + emailFrom + ", email_to:" + emailTo + ", DATE_CHANGED:" + dateChanged;
    }
}

public class ContactJSON {
    private List<ContactObject> data;

    public ContactJSON(List<ContactObject> contactList) {
        this.data = contactList;
    }
}

Then in your main() method you can make use of these classes:

public static void main(String[] args) {
    List<ContactObject> contactList = new ArrayList<ContactObject>();
    ContactObject obj1 = new ContactObject("[email protected]", "[email protected]", "1447666867");
    ContactObject obj2 = new ContactObject("[email protected]", "[email protected]", "1447668867");
    contactList.add(obj1);
    contactList.add(obj2);

    Gson gson = new Gson();
    String json = gson.toJson(new ContactJSON(contactList));
    System.out.println(json);
}

Output:

{"data":[{"emailFrom":"[email protected]","emailTo":"[email protected]","dateChanged":"1447666867"},{"emailFrom":"[email protected]","emailTo":"[email protected]","dateChanged":"1447668867"}]}