Sometimes we need to resize image in Java to fulfil our requirement. You can use the below code to resize image in Java very easily:

1. Define the dimension boundary of which you want resized image as below

Dimension boundary = new Dimension(350, 350); // here you can provide custom height/width

2. Get the Scaled dimension of the image you want to resize. In this method you will pass Original imageSize and boundary.

/**
 * This method will retrieve scaled dimension of an image
 * @param imgSize
 * @param boundary
 * @return
 */
public static Dimension getScaledDimension(BufferedImage imgSize, Dimension boundary) {

    int original_width = imgSize.getWidth();
    int original_height = imgSize.getHeight();
    int bound_width = boundary.width;
    int bound_height = boundary.height;
    int new_width = original_width;
    int new_height = original_height;

    // first check if we need to scale width
    if (original_width > bound_width) {
        //scale width to fit
        new_width = bound_width;
        //scale height to maintain aspect ratio
        new_height = (new_width * original_height) / original_width;
    }

    // then check if we need to scale even with the new height
    if (new_height > bound_height) {
        //scale height to fit instead
        new_height = bound_height;
        //scale width to maintain aspect ratio
        new_width = (new_height * original_width) / original_height;
    }

    return new Dimension(new_width, new_height);
}

3. After getting scaled dimension you can resize you image by using the below method:

 //Read the input stream to a BufferedImage  
   BufferedImage sourceImage = ImageIO.read(in);  

/**
 * This method will resize you image according the provided dimension
 * @param originalImage
 * @param type
 * @param changedSize
 * @return
 */
private  BufferedImage resizeImageWithHint(BufferedImage originalImage, int type, Dimension changedSize){

    BufferedImage resizedImage = new BufferedImage(changedSize.width, changedSize.height, type);
    Graphics2D g = resizedImage.createGraphics();
    g.drawImage(originalImage, 0, 0, changedSize.width, changedSize.height, null);
    g.dispose();    
    g.setComposite(AlphaComposite.Src);

    g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
            RenderingHints.VALUE_INTERPOLATION_BILINEAR);
    g.setRenderingHint(RenderingHints.KEY_RENDERING,
            RenderingHints.VALUE_RENDER_QUALITY);
    g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

    return resizedImage;
}

Hope this will help you.Good Luck :)