How to Build DotCode Reader in Java on Windows 10

A dot code is a 2D barcode symbology composed of disconnected dots. It is widely used in the tobacco industry. Recently, Dynamsoft rolled out barcode reader SDK v7.4, which added DotCode support. In this post, I will share a command-line app and a GUI app, demonstrating how to build Java DotCode reader on Windows 10.

Decoding DotCode in Java Command-Line App

The command-line app is simple. What I am going to do is to invoke an API to decode DotCode from an image file.

Configure Dynamsoft Barcode Reader in pom.xml:

  <repositories>
    <repository>
      <id>dbr</id>
      <url>https://download2.dynamsoft.com/maven/dbr/jar</url>
    </repository>
  </repositories>
  <dependencies>
    <dependency>
      <groupId>com.dynamsoft</groupId>
      <artifactId>dbr</artifactId>
      <version>7.4.0</version>
    </dependency>
  </dependencies>

To simply the running command, we can add a plugin to assemble all dependencies into one jar file:

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>

Instantiate Dynamsoft Barcode Reader and set DotCode as the target barcode:

        BarcodeReader br = null;
        try {
            br = new BarcodeReader("LICENSE-KEY");
            br.initRuntimeSettingsWithString("{\"ImageParameter\":{\"Name\":\"BestCoverage\",\"DeblurLevel\":9,\"ExpectedBarcodesCount\":512,\"ScaleDownThreshold\":100000,\"LocalizationModes\":[{\"Mode\":\"LM_CONNECTED_BLOCKS\"},{\"Mode\":\"LM_SCAN_DIRECTLY\"},{\"Mode\":\"LM_STATISTICS\"},{\"Mode\":\"LM_LINES\"},{\"Mode\":\"LM_STATISTICS_MARKS\"}],\"GrayscaleTransformationModes\":[{\"Mode\":\"GTM_ORIGINAL\"},{\"Mode\":\"GTM_INVERTED\"}]}}", EnumConflictMode.CM_OVERWRITE);
            PublicRuntimeSettings runtimeSettings = br.getRuntimeSettings();
            runtimeSettings.barcodeFormatIds_2 = EnumBarcodeFormat_2.BF2_DOTCODE;
            br.updateRuntimeSettings(runtimeSettings);
        } catch (Exception e) {
            System.out.println(e);
            return;
        }

By default, the SDK will decode all supported barcode formats. If you want to focus on DotCode and speed up the decoding process, disable other 1D and 2D barcode formats:

runtimeSettings.barcodeFormatIds = EnumBarcodeFormat.BF_NULL;

Pass the file path to the decodeFile() function which will soon return the barcode results:

        TextResult[] results = null;
        try {
            results = br.decodeFile(filename, "");
        } catch (Exception e) {
            System.out.println("decode buffered image: " + e);
        }

Build and run the project:

mvn clean install assembly:assembly -Dmaven.test.skip=true

java -cp target/command-line-dotcode-1.0-SNAPSHOT-jar-with-dependencies.jar com.java.barcode.App test.png

A Webcam DotCode Reader Built with OpenCV Java and Java Swing

A GUI app needs more effort.

How to install OpenCV Java?

The OpenCV Java SDK contains a jar package and a shared library. For Windows users, you just need to install the pre-built package and find the OpenCV Java SDK at opencv-4.3\opencv\build\java. Since I’m using a Maven project, I have to install the jar file to the Maven local repository beforehand:

mvn install:install-file -Dfile=opencv-430.jar -DgroupId=org -DartifactId=opencv -Dversion=4.3.0 -Dpackaging=jar

Thereafter, add the configuration to pom.xml:

    <dependency>
      <groupId>org</groupId>
      <artifactId>opencv</artifactId>
      <version>4.3.0</version>
    </dependency>

What about the dll file? If you don’t put the dll in the right place, you will get the error log as loading the library:

Exception in thread "main" java.lang.UnsatisfiedLinkError: no opencv_java430 in java.library.path
        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1867)
        at java.lang.Runtime.loadLibrary0(Runtime.java:870)
        at java.lang.System.loadLibrary(System.java:1122)
        at com.java.barcode.App.main(App.java:65)

Here are the workarounds for the issue.

Check the available java library path. Copy the dll file to current working directory or add the dll path to system environment PATH:

System.out.println(System.getProperty("java.library.path"));

Use the full path to load the library:

System.load("D:/opencv-4.3/opencv/build/java/x64/opencv_java430.dll");

Define the Java library path when running your Java app:

java -Djava.library.path=<dll path> -cp target/opencv-dotcode-1.0-SNAPSHOT-jar-with-dependencies.jar com.java.barcode.App

A “hello world” program using OpenCV Java

Once OpenCV is ready, you can test the library as follows:

System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
Mat mat = Mat.eye(3, 3, CvType.CV_8UC1);
System.out.println("mat = " + mat.dump());

Display Webcam video stream in Java Swing component

Inspired by the OpenCV Java docs that guide JavaFX programming, I studied the OpenCV capture logic and rendered the video frames in a JLable:

public void updateViewer(final BufferedImage image) {
        if (!SwingUtilities.isEventDispatchThread()) {
            SwingUtilities.invokeLater(new Runnable() {
                @Override
                public void run() {
                    mImage.setIcon(new ImageIcon(image));
                }
            });
            return;
        }
    }

Runnable frameGrabber = new Runnable() {

                    @Override
                    public void run() {
                        Mat frame = grabFrame();
                        byte[] data = Utils.matToByteArray(frame);

                        if (!status.get()) {
                            status.set(true);
                            barcodeTimer.schedule(new BarcodeRunnable(frame, mBarcodeReader, callback, status), 0, TimeUnit.MILLISECONDS);
                        }
                    
                        BufferedImage bufferedImage = Utils.byteToBufferedImage(data, frame.width(), frame.height(), frame.channels());
                        if (isRunning) updateViewer(bufferedImage);
                    }
                };
this.timer = Executors.newSingleThreadScheduledExecutor();
this.timer.scheduleAtFixedRate(frameGrabber, 0, 33, TimeUnit.MILLISECONDS);

Read DotCode and show results

In the code above, you can see I created a barcode timer instance for reading DotCode:

barcodeTimer = Executors.newSingleThreadScheduledExecutor();

We have to run the barcode decoding API in a worker thread in order to avoid decreasing the frame rate.

To draw the DotCode position, create a class CustomJLable that extends JLable:

    private ArrayList<Point[]> data = new ArrayList<>();

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g.create();
        if (data.size() > 0) {
            g2d.setColor(Color.RED);
            for (Point[] points : data) {
                for (int i = 0; i < points.length; ++i) {
                    if (i == 3) {
                        g2d.drawLine(points[i].x, points[i].y, points[0].x, points[0].y);
                    } else {
                        g2d.drawLine(points[i].x, points[i].y, points[i + 1].x, points[i + 1].y);
                    }
                }
            }

        }
        g2d.dispose();
    }

    public void appendPoints(Point[] points) {
        data.add(points);
    }

    public void clearPoints() {
        data.clear();
    }

Build and run the GUI DotCode reader:

mvn clean install assembly:assembly -Dmaven.test.skip=true
java -cp target/opencv-dotcode-1.0-SNAPSHOT-jar-with-dependencies.jar com.java.barcode.App
Java DotCode reader

Q&A

How to convert OpenCV Mat to Java byte array?

    public static byte[] matToByteArray(Mat original)
    {
        int width = original.width(), height = original.height(), channels = original.channels();
        byte[] sourcePixels = new byte[width * height * channels];
        original.get(0, 0, sourcePixels);
        return sourcePixels;
    }

How to convert Java byte array to Java BufferedImage?

    public static BufferedImage byteToBufferedImage(byte[] sourcePixels, int width, int height, int channels)
    {
        BufferedImage image = null;
        
        if (channels > 1)
        {
            image = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
        }
        else
        {
            image = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);
        }
        final byte[] targetPixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
        System.arraycopy(sourcePixels, 0, targetPixels, 0, sourcePixels.length);
        
        return image;
    }

Source Code

https://github.com/yushulx/java-dotcode-reader