Google Sheet API V4(Java) append Date in cells

I am tried to add date in cells but sheet automatically store value in string with single quote ('). For Store value in date , We also try to add userEnteredFormat but it didn't work for us.

Below are append request.

{
requests = [{
    appendCells = {
        fields = userEnteredValue,
        userEnteredFormat.numberFormat,
        rows = [{
            values = [{
                userEnteredValue = {
                    numberValue = 10.0
                }
            }, {
                userEnteredValue = {
                    stringValue = Sample String
                }
            }, {
                userEnteredFormat = {
                    numberFormat = {
                        type = DATE
                    }
                },
                userEnteredValue = {
                    stringValue = 2015 - 07 - 13
                }
            }, {
                userEnteredValue = {
                    boolValue = true
                }
            }, {
                userEnteredFormat = {
                    numberFormat = {
                        type = DATE
                    }
                },
                userEnteredValue = {
                    stringValue = 2015 - 07 - 13
                }
            }]
        }],
        sheetId = abc
    }
}]}

Sample Code to append single date cells on sheet

package org.pentaho.googlesheets.api;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.pentaho.di.i18n.BaseMessages;
import org.pentaho.pdi.steps.googlesheets.GoogleSheetsOutputStepMeta;

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.drive.DriveScopes;
import com.google.api.services.sheets.v4.Sheets;
import com.google.api.services.sheets.v4.SheetsScopes;
import com.google.api.services.sheets.v4.model.AppendCellsRequest;
import com.google.api.services.sheets.v4.model.BatchUpdateSpreadsheetRequest;
import com.google.api.services.sheets.v4.model.BatchUpdateSpreadsheetResponse;
import com.google.api.services.sheets.v4.model.CellData;
import com.google.api.services.sheets.v4.model.CellFormat;
import com.google.api.services.sheets.v4.model.ExtendedValue;
import com.google.api.services.sheets.v4.model.NumberFormat;
import com.google.api.services.sheets.v4.model.Request;
import com.google.api.services.sheets.v4.model.RowData;

public class DateIssueSample {

    static String APPLICATION_NAME ;
    static JsonFactory JSON_FACTORY;
    static HttpTransport HTTP_TRANSPORT;
    static List<String> SPREADSHEET_SCOPES ;
    static List<String> DRIVE_SCOPES ;
    static Sheets service;

    static String email = "demo-983@praxis-practice-133423.iam.gserviceaccount.com";
    static String pkey ="E:\\P12Key\\My Project-834a8d37d247.p12";

    public static Credential authorize(List<String> SCOPES ) throws Exception {
        GoogleCredential credential = new GoogleCredential.Builder()
        .setTransport(HTTP_TRANSPORT)
        .setJsonFactory(JSON_FACTORY)
        .setServiceAccountId(email)
        .setServiceAccountScopes(SCOPES)
        .setServiceAccountPrivateKeyFromP12File(new java.io.File(pkey))
        .build();
        credential.refreshToken();

        return credential;

    }
    public static  Sheets getSheetsService() throws Exception {
        Credential credential = authorize(SPREADSHEET_SCOPES);
        return new Sheets.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential)
                .setApplicationName(APPLICATION_NAME)
                .build();
    }
    public static void main(String[] args) throws Exception {
        APPLICATION_NAME = "PDI";
        JSON_FACTORY =new GsonFactory();
        SPREADSHEET_SCOPES =Arrays.asList(SheetsScopes.SPREADSHEETS);
        DRIVE_SCOPES=Arrays.asList(DriveScopes.DRIVE_METADATA_READONLY);
        HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();

        service = getSheetsService();

        String spreadSheetID= "abc";
        Integer sheetID = 123;
        String DateValue = "2015-07-13";

        List<RowData> rowData = new ArrayList<RowData>();
        List<CellData> cellData = new ArrayList<CellData>();

        CellData cell = new CellData();
        cell.setUserEnteredValue(new ExtendedValue().setStringValue(DateValue));
        cell.setUserEnteredFormat(new CellFormat().setNumberFormat(new NumberFormat().setType("DATE")));

        cellData.add(cell);
        rowData.add(new RowData().setValues(cellData));

        BatchUpdateSpreadsheetRequest batchRequests = new BatchUpdateSpreadsheetRequest();
        BatchUpdateSpreadsheetResponse response;
        List<Request> requests = new ArrayList<Request>();      

        AppendCellsRequest appendCellReq = new AppendCellsRequest();
        appendCellReq.setSheetId( sheetID);
        appendCellReq.setRows( rowData );           
        appendCellReq.setFields("userEnteredValue,userEnteredFormat.numberFormat");


        requests = new ArrayList<Request>();
        requests.add( new Request().setAppendCells(appendCellReq));
        batchRequests = new BatchUpdateSpreadsheetRequest();
        batchRequests.setRequests( requests );      


        response=  service.spreadsheets().batchUpdate(spreadSheetID, batchRequests).execute();
        System.out.println("Request \n\n");
        System.out.println(batchRequests.toPrettyString());
        System.out.println("\n\nResponse \n\n");
        System.out.println(response.toPrettyString());
    }

}

SpreadSheet , Sample Code for Single Date value append