Creating a CSV File in java from a HashMap

Question

I have a hashMap in java in terms of some keys which each key is indicating a flow. Then each value showing statics about each packet belongs to that flow.

What I need t

Answer 1

If you really want an Excel file, the best library for creating one is Andy Khan's JExcel.

I think you'd need one worksheet per flow, with .csv pairs for each one, sorted by time.

If these are graphs of a variable versus time, wouldn't "time" be the first value in each pair?

Here's how I'd do it. It works perfectly for the simple test case I supplied - it's working code that you'll be able to extend.

package jexcel;

import jxl.Workbook;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
import jxl.write.WriteException;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class JExcelUtils
{
    public static void main(String[] args)
    {
        String fileName = ((args.length > 0) ? args[0] : "jexcel.xls");
        Map> csv = new HashMap>()
        {{
            put("Flow1", fromArrayToList(new double[][]
            {
                { 0.0, 0.0 },
                { 0.1, 1.0 },
                { 0.2, 2.0 },
                { 0.3, 3.0 },
                { 0.4, 4.0 },
                { 0.5, 5.0 },    
            }));
            put("Flow2", fromArrayToList(new double[][]
            {
                { 0.0, 0.0 },
                { 0.1, 1.0 },
                { 0.2, 4.0 },
                { 0.3, 9.0 },
                { 0.4, 16.0 },
                { 0.5, 25.0 },
            }));
        }};
        WritableWorkbook excelContents = null;

        try
        {
            File excelFile = new File(fileName);
            excelContents = createExcel(excelFile, csv);
            excelContents.write();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        catch (WriteException e)
        {
            e.printStackTrace();
        }
        finally
        {
            try { if (excelContents != null) excelContents.close(); } catch (Exception e) { e.printStackTrace(); }
        }
    }


    public static List fromArrayToList(double [][] input)
    {
        List result = new ArrayList();

        for (int i = 0; i < input.length; ++i)
        {
            result.add(new Pair(input[i][0], input[i][1]));            
        }

        return result;
    }

    public static WritableWorkbook createExcel(File excelFile, Map> worksheets) throws IOException, WriteException
    {
        WritableWorkbook result = Workbook.createWorkbook(excelFile);

        int order = 0;
        for (String worksheetName : worksheets.keySet())
        {
            WritableSheet worksheet = result.createSheet(worksheetName, order++);
            List worksheetValues = worksheets.get(worksheetName);
            for (int row = 0; row < worksheetValues.size(); ++row)
            {
                worksheet.addCell(new jxl.write.Number(0, row, worksheetValues.get(row).getX()));
                worksheet.addCell(new jxl.write.Number(1, row, worksheetValues.get(row).getY()));
            }
        }

        return result;
    }

}


class Pair
{
    private double x;
    private double y;

    Pair(double x, double y)
    {
        this.x = x;
        this.y = y;
    }

    public double getX()
    {
        return x;
    }

    public double getY()
    {
        return y;
    }
}