Convert a JSON of different type of objects into java List object

Question

I have a JSON object stored in db in the form of string. I am using it to create dynamic form in the UI. Now the problem is I want to change some values in it based on other changes happening on the application. So suppose I updated label for the field, then I have to get this JSON and change that here. This would be easy If I have stored same type of objects in this json, but my JSON is like follows:

[{
    "name": "someName",
    "xtype": "keyvaluecombo",
    "fieldLabel": "Some Title",
    "refType": "YES_NO",
    "multiSelect": false,
    "helpText": ""
  },
  {
    "name": "someName2",
    "xtype": "keyvaluecombo",
    "fieldLabel": "Some Title2",
    "refType": "YES_NO",
    "multiSelect": false,
    "helpText": ""
  },
  {
    "xtype": "datefield",
    "fieldLabel": "Joining Date",
    "name": "joiningDate",
    "submitFormat": "Y-m-d"
  },
  {
    "xtype": "userselectioncombo",
    "fieldLabel": "Selection",
    "name": "selections",
    "filterBy": {
      "functions": [
        "select"
      ]
    }
  }]

Now this is stored as String in db, what is efficient way of changing fieldLabel based on name. I could have tried working on it as string only and use regular expression, but that didn't feel right.

Answer 1

Easy to realize that Object in your list have attributes below:

"name"
"xtype"
"fieldLabel"
"refType"
"multiSelect"
"helpText"
"submitFormat"
"filterBy"

So you can create an Object which has over attributes. Using ObjectMapper for deserialize the list:

ObjectMapper mapper = new ObjectMapper();
mapper.readValue(json, new TypeReference<ArrayList<T>>() {})

After have a list object you can loop for change any attribute or change attribute of an specific item you want.

Answer 2

First of all the best way, changing your database design with a new one that suits your model. Not keeping json in your database as a column. But if you can't do that, because sometimes it's impossible to change old db designs you can trace the following way.

And of course you should read your json from db before start and save it again after the below process.

1. Create a custom object that suits your model.

   public class MyObject{
   private String name;
   private String fieldLabel;
   
   public String getFieldLabel(){
       return fieldLabel;
   }
   
   public void setFieldLabel( String fieldLabel ){
       this.fieldLabel = fieldLabel;
   }
   
   public String getName(){
       return name;
   }
   
   public void setName( String name ){
       this.name = name;
   }
   
   // bla bla other fields
   

2. Convert your json into your object, and vice versa see the code example below:

 public static void main( String[] args ){
        Gson gson = new Gson();
        String yourJson = "[{'name':'someName','xtype':'keyvaluecombo','fieldLabel':'Some Title','refType':'YES_NO','multiSelect':false,'helpText':''},{'name':'someName2','xtype':'keyvaluecombo','fieldLabel':'Some Title2','refType':'YES_NO','multiSelect':false,'helpText':''},{'xtype':'datefield','fieldLabel':'Joining Date','name':'joiningDate','submitFormat':'Y-m-d'},{'xtype':'userselectioncombo','fieldLabel':'Selection','name':'selections','filterBy':{'functions':['select']}}]";

        // changing single quotes with double ones.
        yourJson = yourJson.replaceAll( "'", "\"" );

        JsonArray jsonArray = new JsonParser().parse( yourJson ).getAsJsonArray();

        List<MyObject> result = new ArrayList<MyObject>();

        for( JsonElement jsonElement : jsonArray ){
            MyObject myObject = gson.fromJson( jsonElement, MyObject.class );

            // change fields as you wish
            if( myObject.getName().equals( "someName" ) ){
                myObject.setFieldLabel( "TEST" );
            }

            // add it to another list
            result.add( myObject );
        }

        // convert into another json again..
        System.out.println( gson.toJson( result ) );

    }

Answer 3

You should write a bean class, which should be mapping to you Json object like,

public class abc {

    private String name;
    private String xtype;
    private String fieldLabel;
    ........
}

Then you should use

import java.lang.reflect.Type;

GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.create();

Type type = new TypeToken<List<abc>>() {
            }.getType();

List<abc> abcList = gson.fromJson(confTemplate,
                    type); // confTemplate is your Json object you get from DB

this will get the list of beans. 

for (abc abcData : abcList ) {
 // you can do your stuff
}