XStream: Custom Converter for BufferedImage

In the previous tutorials we saw an example of how to convert a java object to XML and back. That tutorial also explained the concept of aliases and implicit collection. While serializing a Java object to XML XStream uses custom converters. These converters specify how to create XML from a Java Object or how to create a Java Object from XML elements. In most cases the provided converters should suffice, however, in certain cases you may want to create your own converters. To do so create a class that implements com.thoughtworks.xstream.converters.Converter and implement the void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context); and Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context); The example below demonstrates a CustomConverter. To make the example more interesting we will write a converter to serialize a BufferedImage. The image for the example can be downloaded from here

package com.studytrails.xml.xstream;

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import javax.imageio.ImageIO;

import org.apache.commons.io.output.ByteArrayOutputStream;

import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.core.util.Base64Encoder;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;

public class CustomConverterExample {

    public static void main(String[] args) throws IOException {
        CustomConverterExample customConverterExample = new CustomConverterExample();
        customConverterExample.showCustomConversionForBufferedImage();
    }

    private void showCustomConversionForBufferedImage() throws IOException {
        Company company = new Company();
        company.setName("Study Trails");
        BufferedImage in = ImageIO.read(new File("st1_200.jpg"));
        BufferedImage newImage = new BufferedImage(in.getWidth(), in.getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D g = newImage.createGraphics();
        g.drawImage(in, 0, 0, null);
        g.dispose();
        company.setImage(newImage);
        XStream xStream = new XStream();
        xStream.registerConverter(new CustomBufferedImageConverter());
        String xml = xStream.toXML(company);

        Company company2 = (Company) xStream.fromXML(xml);
        File outputfile = new File("st2_200.jpg");
        ImageIO.write(company2.image, "jpg", outputfile);

    }

}

class Company {
    String name;
    BufferedImage image;

    public void setName(String name) {
        this.name = name;
    }

    public void setImage(BufferedImage image) {
        this.image = image;
    }
}

class CustomBufferedImageConverter implements Converter {
    @Override
    public boolean canConvert(Class type) {

        return type.isAssignableFrom(BufferedImage.class);
    }

    @Override
    public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
        BufferedImage bufferedImage = (BufferedImage) source;
        try {
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(outStream);
            ImageIO.write(bufferedImage, "jpg", objectOutputStream);
            outStream.flush();
            Base64Encoder encorder = new Base64Encoder();
            String imageString = encorder.encode(outStream.toByteArray());
            outStream.close();
            writer.setValue(imageString);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
        BufferedImage image = null;
        try {
            Base64Encoder encoder = new Base64Encoder();
            byte[] imageBytes = encoder.decode(reader.getValue());
            ObjectInputStream inputStream = new ObjectInputStream(new ByteArrayInputStream(imageBytes));
            image = ImageIO.read(inputStream);
            inputStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return image;
    }
}

(Note: This article’s original links is here )

 XStream: Referencing Objects XStream: Basic Built-in Converters 

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