how solve groovy error java.lang.OutOfMemoryError: GC overhead limit exceeded when I convert xlsx to csv?

Question

I'm using this groovy code for convert xlsx to csv, but I am receiving this error:

java.lang.OutOfMemoryError: GC overhead limit exceeded

I don't know how I could solve this. My code works for a small Excel file of 2mb, but for large excel of more than 20mb it doesn't work. I don't know how set a limit of heap size in groovy.

PLease help me

this is my code

@Grapes(
    @Grab(group='org.apache.poi', module='poi-ooxml', version='3.9')
)
import org.apache.poi.xssf.usermodel.XSSFCell;
@Grapes(
    @Grab(group='org.apache.poi', module='poi-ooxml', version='3.9')
)
@Grapes(
    @Grab(group='org.apache.poi', module='poi', version='3.9')
)
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
import org.apache.poi.openxml4j.exceptions.InvalidFormatException; 
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.io.PrintWriter;
import java.io.File;

    public static void echoAsCSV(Sheet sheet) {
        Row row = null;
        for (int i = 0; i < sheet.getLastRowNum(); i++) {
            row = sheet.getRow(i);
            for (int j = 0; j < row.getLastCellNum(); j++) {
                System.out.print("\"" + row.getCell(j) + "\";");
            }
            System.out.println();
        }
    }


def makeThumbnailx2() {

    /**
     * @param args the command line arguments
     */

        InputStream inp = null;
        try {
            inp = new FileInputStream("venrx.xlsx");
            Workbook wb = WorkbookFactory.create(inp);

            for(int i=0;i<wb.getNumberOfSheets();i++) {
                System.out.println(wb.getSheetAt(i).getSheetName());
                echoAsCSV(wb.getSheetAt(i));
            }
        } catch (InvalidFormatException ex) {
            Logger.getLogger(ExcelReading.class.getName()).log(Level.SEVERE, null, ex);
        } catch (FileNotFoundException ex) {
            Logger.getLogger(ExcelReading.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(ExcelReading.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            try {
                inp.close();
            } catch (IOException ex) {
                Logger.getLogger(ExcelReading.class.getName()).log(Level.SEVERE, null, ex);
            }
        }



}

 makeThumbnailx2()