DisplayImage

Shows a picture the application has - in a database, in a file, wherever - at the size the screen wants it, without sending the original with the page.

DisplayImage avatar = new DisplayImage(new Dimension(64, 64), true);
avatar.setValue(customer.getPhoto());
cp.add(avatar);

• Making one
• It does not send the picture
• Where the picture comes from

Making one

The thumbnail flag is the difference between cropping to a square-ish thumb and scaling the whole picture down: true thumbnails, false scales.

It does not send the picture

The component writes an img tag whose src points back at the component, and serves the picture from a second request:

That has three consequences worth knowing:

• the page stays small, however large the stored picture is;
• each size is resized once and then kept, so a table of a hundred rows showing the same picture resizes it once;
• the url carries a datx timestamp, regenerated whenever the component is built, so a changed picture is never served from the browser's cache.

Where the picture comes from

The value is an IUIImage, an interface with one real method:

public interface IUIImage {
    IUIImageInstance getImage(Dimension size, boolean thumbnail) throws Exception;
    Long getId();
    void setId(Long id);
}

LoadedImage is the implementation the framework ships: a picture in a file, which resizes with ImageMagick and remembers each size it has produced. LoadedImage.create(file, maxSize, null) or create(inputStream, maxSize, null) makes one - so a picture out of a database blob becomes an IUIImage in one line. An application that stores its images elsewhere implements the interface itself.

For a picture that ships with the application - a logo, a diagram - none of this applies: that is an Img pointing at a resource, and the browser fetches and caches it.