Question

86

Remove empty collections from a JSON with Gson

rated 0 times [ 91] [ 5] / answers: 1 / hits: 11643 / 10 Years ago, wed, may 28, 2014, 12:00:00

I want to remove attributes that have empty collections or null values using gson.

Aiperiodo periodo = periodoService();

//periodo comes from a service method with a lot of values

Gson gson = new Gson();

String json = gson.toJson(periodo);

I print json and I have this:

{idPeriodo:121,codigo:2014II,

activo:false,tipoPeriodo:1,

fechaInicioPreMatricula:may 1, 2014,

fechaFinPreMatricula:jul 1, 2014,

fechaInicioMatricula:jul 15, 2014,

fechaFinMatricula:ago 3, 2014,

fechaInicioClase:ago 9, 2014,

fechaFinClase:dic 14, 2014,

fechaActa:ene 15, 2015,

fechaUltModificacion:May 28, 2014 12:28:26 PM,

usuarioModificacion:1,aiAvisos:[],

aiAlumnoCarreraConvalidacionCursos:[],

aiAlumnoMatriculas:[],aiMallaCurriculars:[],

aiAlumnoCarreraEstados:[],aiAdmisionGrupos:[],

aiMatriculaCronogramaCabeceras:[],

aiAlumnoCarreraConvalidacions:[],

aiHorarioHorases:[],aiAsistencias:[],

aiAlumnoPreMatriculas:[],

aiAlumnoMatriculaCursoNotaDetalles:[],

aiOfertaAcademicas:[],aiTarifarios:[]}

For example for that json I don't want to have the collection aiAvisos, there is a way to delete this from the json.
I'm working with a lot of collections actually here I show one, I really need remove these from the json.

I need something like this:

{idPeriodo:121,codigo:2014II,

activo:false,tipoPeriodo:1,

fechaInicioPreMatricula:may 1, 2014,

fechaFinPreMatricula:jul 1, 2014,

fechaInicioMatricula:jul 15, 2014,

fechaFinMatricula:ago 3, 2014,

fechaInicioClase:ago 9, 2014,

fechaFinClase:dic 14, 2014,

fechaActa:ene 15, 2015,

fechaUltModificacion:May 28, 2014 12:28:26 PM,

usuarioModificacion:1}

I tried setting the collections to null, I check the documentation and there's no method there neither...

Please any suggestions.

Thanks a lot who read this!

Answers

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peytont

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1 Year ago

answered 10 Years ago jarod · Accepted Answer

Steps to follow:

Convert the JSON String into Map<String,Object> using Gson#fromJson()

Iterate the map and remove the entry from the map which are null or empty ArrayList or Map.

Form the JSON String back from the final map using Gson#toJson().

Note : Use GsonBuilder#setPrettyPrinting() that configures Gson to output Json that fits in a page for pretty printing.

Sample code:

import java.lang.reflect.Type;

import com.google.gson.Gson;

import com.google.gson.GsonBuilder;

import com.google.gson.reflect.TypeToken;

...  

 

Type type = new TypeToken<Map<String, Object>>() {}.getType();

Map<String, Object> data = new Gson().fromJson(jsonString, type);



for (Iterator<Map.Entry<String, Object>> it = data.entrySet().iterator(); it.hasNext();) {

    Map.Entry<String, Object> entry = it.next();

    if (entry.getValue() == null) {

        it.remove();

    } else if (entry.getValue().getClass().equals(ArrayList.class)) {

        if (((ArrayList<?>) entry.getValue()).size() == 0) {

            it.remove();

        }

    } else if (entry.getValue() instanceof Map){ //removes empty json objects {}

        Map<?, ?> m = (Map<?, ?>)entry.getValue();

        if(m.isEmpty()) {

           it.remove();

        }

    }

}



String json = new GsonBuilder().setPrettyPrinting().create().toJson(data);

System.out.println(json);

output;

  {

    "idPeriodo": 121.0,

    "codigo": "2014II",

    "activo": false,

    "tipoPeriodo": 1.0,

    "fechaInicioPreMatricula": "may 1, 2014",

    "fechaFinPreMatricula": "jul 1, 2014",

    "fechaInicioMatricula": "jul 15, 2014",

    "fechaFinMatricula": "ago 3, 2014",

    "fechaInicioClase": "ago 9, 2014",

    "fechaFinClase": "dic 14, 2014",

    "fechaActa": "ene 15, 2015",

    "fechaUltModificacion": "May 28, 2014 12:28:26 PM",

    "usuarioModificacion": 1.0

  }