Link to another site

A link to a fixed address on another site needs no component: write the <a href="https://..."> in the markup. Use an ExternalLink when the address, or the text of the link, depends on data.

Render a link with a computed URL

Give the anchor a wicket:id:

PersonPage.html

<a wicket:id="search">Search for this person</a>

Create the ExternalLink with the URL as a string or as a model. A model is evaluated each time the page renders, so the link follows changes in the data:

PersonPage.java

IModel<String> searchUrl = personModel.map(person ->
    "https://www.example.org/search?q="
        + URLEncoder.encode(person.getFullName(), StandardCharsets.UTF_8));

add(new ExternalLink("search", searchUrl));

Wicket writes the URL into the href as it is. Encode values that you put in a query string yourself, as above with URLEncoder.

When the model returns null, Wicket does not write an href.

Set the text of the link

The markup between the tags is the default text. Pass a third argument to replace it: a string when the URL is a string, a model when the URL is a model.

add(new ExternalLink("search", searchUrl,
    personModel.map(person -> "Search for " + person.getFullName())));

The text is escaped before it is written.

Open the link in a new tab

Put the attributes in the markup, where they belong to the design:

<a wicket:id="search" target="_blank" rel="noopener noreferrer">Search</a>

rel="noreferrer" also keeps the browser from sending the URL of your page, including a session id in the URL, to the other site. To set attributes from code instead, use an AttributeModifier; see Change a tag’s attributes.

Link to a file in your web application

ExternalLink also links to paths of your own web application that Wicket does not serve, such as a PDF under the webapp root. Call setContextRelative(true), and Wicket makes the path relative to the context root, wherever the current page is:

add(new ExternalLink("manual", "/docs/manual.pdf").setContextRelative(true));

Redirect to another site from code

When the decision is made on the server, for example after a form submit, throw a RedirectToUrlException. Wicket stops processing the request and sends a redirect to the URL:

@Override
protected void onSubmit() {
    String url = paymentProvider.startPayment(order);
    throw new RedirectToUrlException(url);
}