How to upload data using streaming?

Question

My app is used to save sensor data and upload to server.

First I have this data.

data class SensorRecord (val upDown:String,
                     val config:Int,
                     val date: Date,
                     val ms: Int,
                     val dur: Int,
                     public var v:MutableList<SensorValue>
)

data class SensorValue (var accelerometer:Accelerometer? = null,
                        var gyroscope:Gyroscope? = null,
                        var gravity:Gravity? = null,
                        var magnetic:Magnetic? = null,
                        var linearAcceleration:LinearAcceleration? = null,
                        var rotationVector:RotationVector? = null,
                        var gameRotationVector:GameRotationVector? = null,
                        var pressure:Pressure? = null,
                        var orientation:Orientation? = null
){

    data class Accelerometer(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class Gyroscope(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class Gravity(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class Magnetic(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class LinearAcceleration(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class RotationVector(var x:Float,
                             var y:Float,
                             var z:Float,
                             var scalar:Float
    )
    data class GameRotationVector(var x:Float,
                             var y:Float,
                             var z:Float
    )
    data class Pressure(var hpa:Float)
    data class Orientation(var azimuth:Float,
                           var pitch:Float,
                           var roll:Float)
}

And then add many values to list, so the data is very big.

var record:SensorRecord? = null
record = SensorRecord(upDown, config, Date(), ms.toInt(), duration.toInt(), arrayListOf<SensorValue>())

record!!.v.add(sensorValue)
record!!.v.add(sensorValue)
record!!.v.add(sensorValue)
record!!.v.add(sensorValue)
.
.
.
.
add many data

Finally upload to server

fun upload(){
    val gson = GsonBuilder()
            .setDateFormat("yyyy-MM-dd HH-mm-ss")
            .create();
    var jsonString = gson.toJson(record)

    val requestQueue = Volley.newRequestQueue(applicationContext)
    val stringRequest = object : StringRequest(Request.Method.POST, "http://myupload.com",
            object : Response.Listener<String> {
                override fun onResponse(response: String) {
                }
            },
            object : Response.ErrorListener {
                override fun onErrorResponse(error: VolleyError) {
                }
            })
    {
        override fun getParams(): Map<String, String> {
            val params = HashMap<String, String>()
            params["record"] = jsonString
            return params
        }
    }

    requestQueue.add(stringRequest)
}

If data is small, there is no problem, but if the data is big, the app crashes.

Throwing OutOfMemoryError "Failed to allocate a 150994952 byte allocation with 25165824 free bytes and 86MB until OOM, max allowed footprint 135855256, growth limit 201326592"

I found some answer, they suggest to use streaming

java.lang.OutOfMemoryError: Java heap space when try to convert Java Object to Json String

But I don't understand how to use streaming to upload my object

Answer 1

Retrofit has MultiPartBody upload, e.g with POST. Example with File bytes:

val fbody = RequestBody.create(MediaType.parse("image/*"), img) // img is File
val body = MultipartBody.Part.createFormData("file", img.getName(), fbody)

And then Service would accept this MultiPartBody

uploadService.postImageFile(session, body)

The method in interface would look like

@Multipart
@POST("file/put")
Call<ResponseBody> postImageFile(
    @Part("T") String token,
    @Part MultipartBody.Part file);