Convert JSON to POJO having Json property as jsonObject having diffrent property

Question

I have new requirement, I am creating REST API which has dynamic request (actions) and I want to convert that JSON request to POJO, I know how to convert JSON to POJO where key's are same, but not sure what to do when there are different content on objects.

My Json is as follow.

{
  "name":"Workflow",
  "actions": [
    {
      "name": "EDIT_PROPERTY",
      "payload": {
        "name": "city",
        "value": "Pune"
      }
    },
    {
      "name":"SEND_EMAIL",
      "payload":{
        "from":"[email protected]",
        "to":"[email protected]",
        "subject":"Try email",
        "body":"content"
      }
    },
    {
      "name":"CREATE_TASK",
      "payload":{
        "user":1,
        "type":"call",
        "status":"open",
        "note":"This is  note content"
      }
    }
  ]
}

As you can see actions are set of Objects which has name and payload, now payload has different fields, I have predefined names. and each payload under action has predefined keys as you see.

I want to convert this to POJO something like

class Workflow{
    String name;
    Set<Action> actions;
}

class Action {
    String name;
    //What to add as payload
}

Thanks

Alpesh

Answer 1

This is what you can do :

JSON to POJO model :

@Data
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Event {
    public String name;
    public List<Action> actions;


    @Data
    public static class Action {
        public String name;
        Map<String, Object> payload;
    }


}

public class TestJson {

    private static String json = "{\n" +
            "  \"name\":\"Workflow\",\n" +
            "  \"actions\": [\n" +
            "    {\n" +
            "      \"name\": \"EDIT_PROPERTY\",\n" +
            "      \"payload\": {\n" +
            "        \"name\": \"city\",\n" +
            "        \"value\": \"Pune\"\n" +
            "      }\n" +
            "    },\n" +
            "    {\n" +
            "      \"name\":\"SEND_EMAIL\",\n" +
            "      \"payload\":{\n" +
            "        \"from\":\"[email protected]\",\n" +
            "        \"to\":\"[email protected]\",\n" +
            "        \"subject\":\"Try email\",\n" +
            "        \"body\":\"content\"\n" +
            "      }\n" +
            "    },\n" +
            "    {\n" +
            "      \"name\":\"CREATE_TASK\",\n" +
            "      \"payload\":{\n" +
            "        \"user\":1,\n" +
            "        \"type\":\"call\",\n" +
            "        \"status\":\"open\",\n" +
            "        \"note\":\"This is  note content\"\n" +
            "      }\n" +
            "    }\n" +
            "  ]\n" +
            "}";

    @SneakyThrows
    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();
        Event event = objectMapper.readValue(json, Event.class);
        System.out.println(event);

    }


}

When debugging, you'll notice that our objects have been filled accordingly:

Answer 2

Well, generally, I prefer any solution that does not involve Component Annotations. This is my own personal preference because eliminating constructors and method parameters is usually a giant headache. This is based on 1999 - 2006 Java Programming experience. If you have a need to dynamically generate classes and constructors or getters, then you may easily ignore or delete this answer. For me, JSON Parsing is practice right now.

In this posted answer, I have used the older Java JSON Library whose JavaDoc may be viewed here: javax.json.*. Here is my solution. It requires / expects that you write:

• Your own toString() methods for your JSON Data Classes
• Your own retrieve operations

The following code has output, and that is included at the end of this post. Usually I include a lot of Code Documentation. However, when the code is strictly parsing data, the code itself is usually so legible that more comments would clutter the retrieve and the toString() operations, so I have left them as is.

import java.util.*;
import javax.json.*;
import java.io.*;

public class Messages
{
    public abstract static class Action
    {
        public final String name;
        public Action(String name) { this.name=name; }
    }

    public static class EditProperty extends Action
    {
        public final String propName, propValue;

        public EditProperty(String name, String value)
        { super("EDIT_PROPERTY"); this.propName=name; this.propValue=value; }

        public String toString()
        { 
            return 
                "Action:   " + name         + '\n' + 
                "Name:     " + propName     + '\n' +
                "Value:    " + propValue    + '\n';
        }
    }

    public static class SendEmail extends Action
    {
        public final String from, to, subject, body;

        public SendEmail(String from, String to, String subject, String body)
        { super("SEND_EMAIL"); this.from=from; this.to=to; this.subject=subject; this.body=body; }

        public String toString()
        {
            return
                "Action:   "    + name      + '\n' +
                "From:     "    + from      + '\n' +
                "To:       "    + to        + '\n' +
                "Subject:  "    + subject   + '\n' +
                "Body:     "    + body      + '\n';
        }
    }

    public static class CreateTask extends Action
    {
        public final int user;
        public final String type, status, note;

        public CreateTask(int user, String type, String status, String note)
        { super("CREATE_TASK"); this.user=user; this.type=type; this.status=status; this.note=note; }

        public String toString()
        {
            return
                "Action:   " + name     + '\n' +
                "User:     " + user     + '\n' +
                "Type:     " + type     + '\n' +
                "Status:   " + status   + '\n' +
                "Note:     " + note     + '\n';
        }
    }

    public static void main(String[] argv) throws IOException
    {
        Vector<Action>  actions     = new Vector<>();
        Reader          r           = new FileReader("in.json");

        JsonArray       actionList  = Json
            .createReader(r)
            .readObject()
            .getJsonArray("actions");

        for (JsonObject actionObj : actionList.getValuesAs(JsonObject.class))
        {
            JsonObject  payload = actionObj.getJsonObject("payload");
            Action      action  = null;

            switch (actionObj.getString("name"))
            {
                case "EDIT_PROPERTY"    :   action = new EditProperty(
                                                payload.getString("name"),
                                                payload.getString("value")
                                            ); break;
                case "SEND_EMAIL"       :   action = new SendEmail(
                                                payload.getString("from"),
                                                payload.getString("to"),
                                                payload.getString("subject"),
                                                payload.getString("body")
                                            ); break;
                case "CREATE_TASK"      :   action = new CreateTask(
                                                payload.getInt("user"),
                                                payload.getString("type"),
                                                payload.getString("status"),
                                                payload.getString("note")
                                            ); break;
            }
            
            actions.add(action);
        }
        
        for (Action action : actions) System.out.println(action);
    }
}

The class and inner-classes above would produce this output when invoked at the command line:

@cloudshell:~$ java Messages 
Action:   EDIT_PROPERTY
Name:     city
Value:    Pune

Action:   SEND_EMAIL
From:     [email protected]
To:       [email protected]
Subject:  Try email
Body:     content

Action:   CREATE_TASK
User:     1
Type:     call
Status:   open
Note:     This is  note content

Answer 3

The JSON you show is actually a list of one object type; specifically, the payload is just a Map of String to Object.

Once you parse the JSON, your code will need to process each "different" payload type based on the payload type.

Here is some sample code:

public class BlamMessage
{
    private String name;
    private Map<String, Object> payload;

    ...
}

public class MessageHolder
{
    @JsonProperty("actions")
    private List<BlamMessage> messageList;

    private String name;

    ...
}