Understanding the iText BarcodeInter25 method

One of the cooler aspects of the Creating a wicked Film Festival VIP Pass with iText example was the use of bar codes. Not being familiar with them, or the BarcodeInter25 method used in the example, I did some searching. Thanks to wikipedia and barcode-1.net I discovered that the iText method generates a bar code in a standard format known as Interleaved 2 of 5.

Inter-whaaat?

The Interleaved 2 of 5 format is used to encode pairs of numbers using a set of bars. Each number, 0 through 9, is represented by a set of 5 bars. The number zero is represented by NNWWN, where "N" is a narrow bar and "W" is a wide bar.


0 NNWWN
1 WNNNW
2 NWNNW
3 WWNNN
4 NNWNW
5 WNWNN
6 NWWNN
7 NNNWW
8 WNNWN
9 NWNWN

The term interleaved means that two numbers are encoded in a set of 5 bars and the spaces in between those bars. The first number is represented by the black bars. The second number is represented by the spaces in between the bars. This bar code format begins with a start code NNNN and ends with a stop code WNN.

Because I am curious *cough* geek *cough* , I created a simple bar code to test this information. As you can see this is the bar code I generated.



After counting the bars things seemed to match up, but then I remembered the descriptions said this format encodes pairs of numbers. My sample number contained 7 digits, so why did it work? Then I remembered the sample code adds a checksum digit. So my 7 digit number plus the 1 digit checksum produces an even number of digits to encode.

How is the checksum calculated

According to barcode-1.net this format uses the modulo 10 scheme to calculate the checksum. So I took my sample number and calculated what the checksum digit should be.

My base number is: 0012345

1. Add the digits in odd numbered positions: 0 + 1 + 3 + 5 == 9
2. Multiply the result by three: 9 x 3 == 27
3. Add the digits in even numbered positions: 0 + 2 + 4 == 6
4. Add the two results together: 6 + 27 == 33
5. Calculate modulo: 33 mod 10 == 3
6. Subtract the modulo from ten: 10 - 3 == 7

The checksum for this number is: 7

I checked it against my sample bar code and it matched.



There are additional rules about the dimensions of the bars, but I will leave you to read more about it on your own. If you would like to generate a sample bar code PDF in ColdFusion, see the code below.

As usual these ramblings are based on my own unofficial reading, testing and observations. So corrections/questions/suggestions are welcome ;)

ColdFusion Code

<h1>Simple Bar Code Example</h1>

<cfscript>
    savedErrorMessage = "";
 
    // cfSearching: All file paths are relative to the current directory
    fullPathToOutputFile = ExpandPath("./SimpleBarCodeExample.pdf");
    fullPathToITextJar = ExpandPath("./iText-2.0.7.jar");
    dotNotationPathToJavaLoader = "javaloader.JavaLoader";
    barCodeNumber = "0012345";
        
    // cfSearching: get an instance of the javaloader
    pathsForJavaLoader = arrayNew(1);
    arrayAppend(pathsForJavaLoader, fullPathToITextJar);
    javaLoader = createObject("component", dotNotationPathToJavaLoader).init(pathsForJavaLoader);

    // cfSearching: create color and font used for drawing text
    color = createObject("java", "java.awt.Color");    
    BLACK = color.init(javacast("int", 0), javacast("int", 0), javacast("int", 0) );
    BaseFont = javaLoader.create("com.lowagie.text.pdf.BaseFont");
    FONT = javaLoader.create("com.lowagie.text.FontFactory").getFont(BaseFont.HELVETICA,
            BaseFont.WINANSI, BaseFont.NOT_EMBEDDED).getBaseFont();
    
    try {
        // cfSearching: create a document with a custom page size 4 inches x 3 inches
        pageDimensions = javaLoader.create("com.lowagie.text.Rectangle").init( inchesToPoints(4), inchesToPoints(3));
        document = javaLoader.create("com.lowagie.text.Document").init(pageDimensions);

        // we create a writer that listens to the document and directs a PDF-stream to a file        
        outStream = createObject("java", "java.io.FileOutputStream").init(fullPathToOutputFile);
        writer = javaLoader.create("com.lowagie.text.pdf.PdfWriter").getInstance(document, outStream);

        // step 3
        document.open();
        // step 4
        directContent = writer.getDirectContent();

        directContent.beginText();
        directContent.moveText(inchesToPoints(0.25), HEIGHT - inchesToPoints(0.75));
        directContent.setFontAndSize(FONT, javacast("float", 16) );
        directContent.setColorFill(BLACK);
        directContent.showText("Barcode number: "& barCodeNumber);
        directContent.endText();
        
        Rectangle = javaLoader.create("com.lowagie.text.Rectangle");
        PushbuttonField = javaLoader.create("com.lowagie.text.pdf.PushbuttonField");
        barcode = PushbuttonField.init(writer, rectangle.init( inchesToPoints(0.25), 
                        inchesToPoints(1), 
                        WIDTH - inchesToPoints(0.25), 
                        HEIGHT - inchesToPoints(1)), 
                        "barcode");
        
        
        // cfSearching: generate the barcode image. does nothing if code is invalid
        try {
            code = javaLoader.create("com.lowagie.text.pdf.BarcodeInter25").init();
            code.setGenerateChecksum(true);
            code.setBarHeight( inchesToPoints(1) );

            code.setCode( javacast("string", barCodeNumber) );
            code.setFont( javacast("null", "") );
            cb = javaLoader.create("com.lowagie.text.pdf.PdfContentByte").init(writer);
            template = code.createTemplateWithBarcode(cb,  javacast("null", ""),  javacast("null", ""));
            barcode.setLayout(PushbuttonField.LAYOUT_ICON_ONLY);
            barcode.setProportionalIcon(false);
            barcode.setTemplate(template);
            writer.addAnnotation(barcode.getField());

        } catch (java.lang.Exception e) {
            // not a valid code, do nothing
        }

    }
    catch (com.lowagie.text.DocumentException de) {
        savedErrorMessage = de;
    } 
    catch (java.io.IOException ioe) {
        savedErrorMessage = ioe;
    }

    // step 4 
    document.close();
    outStream.close();
</cfscript>

<!--- show any errors --->
<cfif len(savedErrorMessage) gt 0>
    Error - unable to create document
    <cfdump var="#savedErrorMessage#">
</cfif>

<cffunction name="inchesToPoints" returntype="numeric" access="public" output="false"
                hint="Converts inches to Postscript points">
    <cfargument name="inches" type="numeric" required="true">
    <cfreturn javacast("float", (arguments.inches * 72)) >
</cffunction>