Grouping elements based on common element to form a json array of objects

Question

im getting my data as whole json,but i expect it to be grouped based on a common element among the result itself

Data from query

firststring	secondstring	thirdstring
My Account	MyAccount	Menu1
My Cart	MyFavourites	Menu1
My Status	Status	Menu1
Orders	orders	Menu2
Damage Claim	DamageClaim	Menu2

my bean class

    public class CommonThreeString implements Serializable{

        private String firstString;
        private String secondString;
        private String thirdString;
        
        public String getFirstString() {
            return firstString;
        }
        public void setFirstString(String firstString) {
            this.firstString = firstString;
        }
        public String getSecondString() {
            return secondString;
        }
        public void setSecondString(String secondString) {
            this.secondString = secondString;
        }
        public String getThirdString() {
            return thirdString;
        }
        public void setThirdString(String thirdString) {
            this.thirdString = thirdString;
        }
    }

My controller

        @PostMapping("getMenuList")
    public String getMenuList() throws ServiceException {
        ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
        String json = null;
        try {
            json = ow.writeValueAsString(iService.getMenuList());
        } catch (JsonProcessingException e) {
        }

        return json;
    }

service implementation

        public List<CommonThreeString> getMenuList() throws ServiceException {
    
        List<CommonTwoLongThreeString> menuList = null;
        try {
            menuList =  Impl.getMenuListByPortalId(Long.valueOf("input"));
            //query works done here//
        } catch (ServiceException e) {
        }
        return menuList;
    }

here im getting output as

 [   
      {
        "firstString": "My Account",
        "secondString": "MyAccount",
        "thirdString": "Menu1"
      },
      {
        "firstString": "My Cart",
        "secondString": "MyFavourites",
        "thirdString": "Menu1"
      },
      {
        "firstString": "My Status",
        "secondString": "Status",
        "thirdString": "Menu1"
      },
      {
        "firstString": "orders",
        "secondString": "orders",
        "thirdString": "Menu2"
      },
      {
        "firstString": "Damage Claim",
        "secondString": "DamageClaim",
        "thirdString": "Menu2"
      }
    ]

The output im expecting

    Menu1
    [   
      {
        "firstString": "My Account",
        "secondString": "MyAccount",
        --"thirdString": "Menu1"
      },
      {
        "firstString": "My Cart",
        "secondString": "MyFavourites",
        --"thirdString": "Menu1"
      },
      {
        "firstString": "My Status",
        "secondString": "Status",
        --"thirdString": "Menu1"
      }
      ]
      Menu2
      [
      {
        "firstString": "orders",
        "secondString": "orders",
        --"thirdString": "Menu2"
      },
      {
        "firstString": "Damage Claim",
        "secondString": "DamageClaim",
        --"thirdString": "Menu2"
      }
    ]

the third String need to be the grouping factor

im want to group properly like the above thanks in advance

Senthil · Accepted Answer · 2022-04-01 07:51:28Z

import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import com.fasterxml.jackson.databind.ObjectMapper;

import com.google.gson.*;

public class TestJson {
    public static void main(String[] args) {
        String jsonString = null;
        try {
            jsonString = "[\n"
                    + "    {\n"
                    + "        \"firstString\": \"My Account\",\n"
                    + "        \"secondString\": \"MyAccount\",\n"
                    + "        \"thirdString\": \"Menu1\"\n"
                    + "    },\n"
                    + "    {\n"
                    + "        \"firstString\": \"My Cart\",\n"
                    + "        \"secondString\": \"MyFavourites\",\n"
                    + "        \"thirdString\": \"Menu1\"\n"
                    + "    },\n"
                    + "    {\n"
                    + "        \"firstString\": \"My Status\",\n"
                    + "        \"secondString\": \"Status\",\n"
                    + "        \"thirdString\": \"Menu1\"\n"
                    + "    },\n"
                    + "    {\n"
                    + "        \"firstString\": \"orders\",\n"
                    + "        \"secondString\": \"orders\",\n"
                    + "        \"thirdString\": \"Menu2\"\n"
                    + "    },\n"
                    + "    {\n"
                    + "        \"firstString\": \"Damage Claim\",\n"
                    + "        \"secondString\": \"DamageClaim\",\n"
                    + "        \"thirdString\": \"Menu2\"\n"
                    + "    }\n"
                    + "]";
            
            ObjectMapper mapper = new ObjectMapper();


            com.google.gson.JsonArray dataArray = new JsonParser().parse(jsonString).getAsJsonArray();

            HashMap<String, List<CommonThreeString>> groupByFieldMap = new HashMap<String, List<CommonThreeString>>();

            for (JsonElement element : dataArray) {
                String groupField = element.getAsJsonObject().get("thirdString").getAsString();
                String firstStr = element.getAsJsonObject().get("firstString").getAsString();
                String secondStr = element.getAsJsonObject().get("secondString").getAsString();
                String thirdStr = element.getAsJsonObject().get("thirdString").getAsString();
                if (groupByFieldMap.containsKey(groupField)) {
                    groupByFieldMap.get(groupField).add(new CommonThreeString(firstStr, secondStr, thirdStr));
                } else {
                    ArrayList<CommonThreeString> emptyList = new ArrayList<CommonThreeString>();
                    emptyList.add(new CommonThreeString(firstStr, secondStr, thirdStr));
                    groupByFieldMap.put(groupField, emptyList);
                }
            }

            StringWriter result = new StringWriter();
            mapper.writeValue(result, groupByFieldMap);
            System.out.println(result.toString());
            
            
        } catch (Exception e) {
            System.out.println("Exception "+e.getStackTrace());
        }

    }

}

Ref Here : how to do it

Grouping Json response with keys in java - android studio

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