Java: convert image to byte array, convert byte array to image

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Convert image to byte array There are some situations where we need to convert an image to a byte array. The following are the java code for converting an image to a byte array, and then convert byte array back to image. I have tested it under Java 1.5, please leave your comment, if there is any problem.

This program was initially for a centralized file upload and management system, which uses Web Service to do file transfer. Although Web Service is not good for transferring large files, images are normally smaller, and therefore may works this way. On one side, the image is converted to an array of bytes, and sent to the other side. Then the other side convert the byte array back to the image.

If you are interested in transferring images using Web Service, Please read my previous post about this topic. Here is a post about the solution of using Web Service to transfer files.

You can download the code here or copy below.

import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
 
import java.util.Iterator;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;
 
public class ConvertImage {
 
    public static void main(String[] args) throws FileNotFoundException, IOException {
    	/*
    	 * In this function the first part shows how to convert an image file to 
    	 * byte array. The second part of the code shows how to change byte array
    	 * back to a image
    	 */
        File file = new File("C:\\rose.jpg");
        System.out.println(file.exists() + "!!");
 
        FileInputStream fis = new FileInputStream(file);
        //create FileInputStream which obtains input bytes from a file in a file system
        //FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.
 
        //InputStream in = resource.openStream();
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        byte[] buf = new byte[1024];
        try {
            for (int readNum; (readNum = fis.read(buf)) != -1;) {
                bos.write(buf, 0, readNum); 
                //no doubt here is 0
                /*Writes len bytes from the specified byte array starting at offset 
                off to this byte array output stream.*/
                System.out.println("read " + readNum + " bytes,");
            }
        } catch (IOException ex) {
            Logger.getLogger(ConvertImage.class.getName()).log(Level.SEVERE, null, ex);
        }
        byte[] bytes = bos.toByteArray();
        //bytes is the ByteArray we need
 
 
        /*
         * The second part shows how to convert byte array back to an image file  
         */
 
 
        //Before is how to change ByteArray back to Image
        ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
        Iterator<?> readers = ImageIO.getImageReadersByFormatName("jpg");
        //ImageIO is a class containing static convenience methods for locating ImageReaders
        //and ImageWriters, and performing simple encoding and decoding. 
 
        ImageReader reader = (ImageReader) readers.next();
        Object source = bis; // File or InputStream, it seems file is OK
 
        ImageInputStream iis = ImageIO.createImageInputStream(source);
        //Returns an ImageInputStream that will take its input from the given Object
 
        reader.setInput(iis, true);
        ImageReadParam param = reader.getDefaultReadParam();
 
        Image image = reader.read(0, param);
        //got an image file
 
        BufferedImage bufferedImage = new BufferedImage(image.getWidth(null), image.getHeight(null), BufferedImage.TYPE_INT_RGB);
        //bufferedImage is the RenderedImage to be written
        Graphics2D g2 = bufferedImage.createGraphics();
        g2.drawImage(image, null, null);
        File imageFile = new File("C:\\newrose2.jpg");
        ImageIO.write(bufferedImage, "jpg", imageFile);
        //"jpg" is the format of the image
        //imageFile is the file to be written to.
 
        System.out.println(imageFile.getPath());
    }
}

Here is a simple version which has exactly the same function. It uses the BufferedImage class, which is a proved more efficient way.

Java: convert image to byte array, convert byte array to image

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