Create an Excel File using Java and POI

To create an Excel file in Java we can use Apache's POI library. The example file created by the following example code demostrates how to add a String, a Date, a Boolean, and a Number to specified cells in the spreadsheet. First a HSSFWorkbook object is created and a HSSFSheet object is added. A HSSFRow is added to the sheet, and a HSSFCell is added to the row. To add a String to the cell, a HSSFRichTextString is used. To add a Date to the cell, a HSSFCellStyle is used in conjunction with a HSSFDataFormat object appied to a Date object. A Boolean value and a Number value are added directly to the cell. The following sample code was successfully tested with POI versions 3.6 and 3.7.

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Date;

import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFCellStyle;
import org.apache.poi.hssf.usermodel.HSSFDataFormat;
import org.apache.poi.hssf.usermodel.HSSFRichTextString;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;

// The following example code demonstrates how to create an Excel  
// file using the org.apache.poi library. In the sample file,
// a String, Date, Boolean, and Number are added to individual cells
// in the spreadsheet.

public class CreateExcelFile {

    public static void main(String[] args) {

        HSSFWorkbook workbook = new HSSFWorkbook();

        HSSFSheet firstSheet = workbook.createSheet("Sheet 1");

        // Write a String in Cell 1A
        HSSFRow row1 = firstSheet.createRow(0);
        HSSFCell cell1A = row1.createCell(0);
        cell1A.setCellValue(new HSSFRichTextString("Sample String"));

        // Write a Date in Cell 2B
        HSSFRow row2 = firstSheet.createRow(1);
        HSSFCell cell2B = row2.createCell(1);
        cell2B.setCellValue(new Date());
        // Format the Date so it looks like a date
        HSSFCellStyle cellStyle = workbook.createCellStyle();
        cellStyle = workbook.createCellStyle();
        cellStyle.setDataFormat(HSSFDataFormat.getBuiltinFormat("m/d/yy h:mm"));
        cell2B.setCellStyle(cellStyle);

        // Write a Boolean in Cell 3C
        HSSFRow row3 = firstSheet.createRow(2);
        HSSFCell cell3C = row3.createCell(2);
        cell3C.setCellValue(true);

        // Write a Number in Cell 4D
        HSSFRow row4 = firstSheet.createRow(3);
        HSSFCell cell4D = row4.createCell(3);
        cell4D.setCellValue(3.14);

        FileOutputStream fileOutputStream = null;
        try {
            fileOutputStream = new FileOutputStream(new File("/Temp/Test3.xls"));
            workbook.write(fileOutputStream);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.flush();
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Here is a screenshot of the generated Excel File:

Piece of cake!!!

Mars Science Laboratory (Curiosity Rover) Mission Animation

Get Sheet Names from an Excel File Using Java and POI

To get the sheet names from an Excel file in Java we can use Apache's POI library. First a file is imported from disk passing a FileInputStream object to a org.apache.poi.hssf.usermodel.HSSFWorkbook object. Looping over each sheet in the Excel spreadsheet, the sheet name is determined using the workbook.getSheetName() method. The following sample code was successfully tested with POI versions 3.6 and 3.7.

Here is a screenshot of the test file I used for this example:

import java.io.FileInputStream;
import java.io.IOException;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;

// The following example code demonstrates how to get the Sheet
// names in an Excel spreadsheet file

public class GetExcelSheetNames {

    public static void main(String[] args) {

        FileInputStream fileInputStream = null;
        try {
            fileInputStream = new FileInputStream("/Temp/Test1.xls");

            HSSFWorkbook workbook = new HSSFWorkbook(fileInputStream);

            // for each sheet in the workbook
            for (int i = 0; i < workbook.getNumberOfSheets(); i++) {

                System.out.println("Sheet name: " + workbook.getSheetName(i));
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

Here is the output of the program:

Sheet name: Sheet1
Sheet name: Sheet2
Sheet name: Sheet3

Piece of cake!!!

SAWSTOP - Inventor Puts His Own Finger in the Table Saw

The Inner Life of a Cell [HQ]

Validate a URL in Java

To validate a URL String in Java we can use the java.net.URL object. First a URL object is created, passing the URL String to its constructor. If the URL String is malformed or invalid, a MalformedURLException will be thrown indicating a malformed URL. Next the URL is converted to a URI using the toURI() method. If URL is not formatted strictly according to to RFC2396 and cannot be converted to a URI, a URISyntaxException will be thrown indicating a malformed URL. The following code demonstrates how to validate a URL String.

package url;

import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.net.URL;

//
// The following example code demonstrates how to
// check if a given URL is valid or not.
//
public class CheckURLValidity {

    public static void main(String[] args) {

        String testURLString = "https://thermodynamiccomputing.com/main?&t=20&f=52";
        System.out.println(isValidURL(testURLString));

        testURLString = "http6://thermodynamiccomputing.com/";
        System.out.println(isValidURL(testURLString));

        testURLString = "http://thermodynamiccomputing.com/   dd";
        System.out.println(isValidURL(testURLString));

        testURLString = "http://<thermodynamiccomputing.com";
        System.out.println(isValidURL(testURLString));
    }

    private static boolean isValidURL(String pUrl) {

        URL u = null;
        try {
            u = new URL(pUrl);
        } catch (MalformedURLException e) {
            return false;
        }
        try {
            u.toURI();
        } catch (URISyntaxException e) {
            return false;
        }
        return true;
    }

}

Here is the output of the example code:

true
false
false
false

Piece of cake!!!

Get Domain Name from a URL String in Java

To get the domain name or sub-domain name from a URL String in Java we can use the java.net.URL object. First a URL object is created, passing the URL String to its constructor. If the URL String is malformed or invalid, a MalformedURLException will be thrown. The getHost() method is then used to pull only the part of the URL containing the domain name. The following code demonstrates getting the domain name from a URL String.

import java.net.MalformedURLException;
import java.net.URL;

//
// The following example code demonstrates how to
// get the domain name from a URL String
//
public class GetDomainNameFromURL {

    public static void main(String[] args) throws MalformedURLException {

        String testURLString = "https://thermodynamiccomputing.com/main?&t=20&f=52";
        URL lURL = new URL(testURLString);
        String hostName = lURL.getHost();
        System.out.println(hostName);

        testURLString = "http://www.thermodynamiccomputing.com/main?&t=20&f=52";
        lURL = new URL(testURLString);
        hostName = lURL.getHost();
        System.out.println(hostName);

        testURLString = "http://www.sub.thermodynamiccomputing.com/main?&t=20&f=52";
        lURL = new URL(testURLString);
        hostName = lURL.getHost();
        System.out.println(hostName);

    }
}

Here is the output of the example code:

thermodynamiccomputing.com
www.thermodynamiccomputing.com
www.sub.thermodynamiccomputing.com

Piece of cake!!!

Spherical Flying Machine Developed by Japan Ministry Of Defense

A White Blood Cell Capturing a Bacterium

Java Web Apps - Integrating Charts into a Servlet

Adding a chart to a Java web application is really easy to do - thanks to the open source Java charting API XChart. XChart's charting library lets you very easily make charts an integrate them into all your Java-based applications. In this blog post, I am going to demonstrate how to add charts to a Java web application. If you want to integrate XChart charts in your Java applications, download the JAR here. You can also see more XChart exmaples here.

The Basic Idea

The basic idea for adding XChart charts to a web app is as follows. First, you have a JSP or HTML page with a link on it that will request a new page with a chart. The new JSP or HTML page that is generated has an img tag in it with a reference to an in-memory chart stored in a HashMap in a Servlet that maps the reference and the chart. When the page reloads, the browser parses the img tag and subsequently requests the image from the Servlet. The Servlet then streams the chart to the browser and it is rendered on the page.

An Example

If the basic idea explanation above did not make complete sense, the following example should make it clear.

Step 1: ChartServlet. This Servlet does one of two things in the doGet() method, depending on the request. If it receives and 'action', it generates a chart. Here you could pass in different 'action' parameters to create different charts if you want. If it receives a 'chart_id', it pulls the chart from CHART_MAP and streams it out to the browser.

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.xeiam.xcharts.BitmapEncoder;
import com.xeiam.xcharts.Chart;
import com.xeiam.xcharts.QuickChart;

@javax.servlet.annotation.WebServlet(name = "ChartServlet", urlPatterns = { "/chart" })
public class ChartServlet extends HttpServlet {

    private static Map<String, Chart> CHART_MAP = new HashMap<String, Chart>();

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // generate the Chart
        String action = request.getParameter("action");
        if (action != null && !action.equals("null")) {
            String chartId = generateRandomChart();
            request.setAttribute("chart_id", chartId);
            request.getRequestDispatcher("/chart.jsp").forward(request, response);
        }

        // Fetch the Chart
        String chartId = request.getParameter("chart_id");
        if (chartId != null && !chartId.equals("null")) {

            Chart chart = CHART_MAP.get(chartId);
            if (chart != null) {
                response.setContentType("image/png");
                ServletOutputStream out = response.getOutputStream();
                try {
                    BitmapEncoder.streamPNG(out, chart);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                out.close();
                chart = null;
                CHART_MAP.remove(chartId);
            } else {
                System.err.println("CHART NOT FOUND!!!");
            }
        }
    }

    // generate the chart
    public static String generateRandomChart() {
        Chart chart = QuickChart.getChart("XChart Sample - Random Walk", "X", "Y", null, null, getRandomWalk(105));
        String uuid = UUID.randomUUID().toString();
        CHART_MAP.put(uuid, chart);
        return uuid;
    }

    // generate random walk data set
    private static double[] getRandomWalk(int numPoints) {
        double[] y = new double[numPoints];
        y[0] = 0;
        for (int i = 1; i < y.length; i++) {
            y[i] = y[i - 1] + Math.random() - .5;
        }
        return y;
    }
}

Step 2: Chart JSP. To request and display the Chart, the JSP contains two DIVs - one for a link to request the chart and one for a IMG tag to display the Chart image. I named this JSP chart.jsp.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
 <head>
     <meta http-equiv="content-type" content="text/html;charset=utf-8" />
     <% String chartId = (String) request.getAttribute("chart_id");%>
 </head>
    <body>
     <div>
      <a href="<%=request.getContextPath()%>/chart?action=whatever">Generate Chart</a>
     </div>
     <%if(chartId != null){ %>
     <div>
      <img src="<%=request.getContextPath()%>/chart?chart_id=<%=chartId %>"/> 
     </div>
  <%} %>
    </body>
</html>

Step 3: Test it. Now deploy your webapp with the new Servlet and JSP and in your browser go to: http://localhost/YourWebAppContext/chart.jsp

After clicking on 'Generate Chart' your chart will appear on the web page. Each time you click it, a new chart will show up.

Piece of Cake!!!

See also: Java XChart Library Now Supports Error Bars