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68 lines
2.0 KiB
Plaintext
68 lines
2.0 KiB
Plaintext
---
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title: Generating Dynamic Resources Based On URI Or Parameters
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order: 28
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layout: page
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---
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[[generating-dynamic-resources-based-on-uri-or-parameters]]
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Generating dynamic resources based on URI or parameters
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-------------------------------------------------------
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You can dynamically generate responses based on e.g. query parameters by
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creating your own `RequestHandler` and registering it with the session.
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In this way, you can for instance create an image that draws a text,
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given as a parameter to the image. This has been done in the example
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below:
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[source,java]
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....
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public class DynamicImageUI extends UI {
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public static final String IMAGE_URL = "myimage.png";
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private final RequestHandler requestHandler = new RequestHandler() {
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@Override
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public boolean handleRequest(VaadinSession session,
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VaadinRequest request, VaadinResponse response)
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throws IOException {
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if (("/" + IMAGE_URL).equals(request.getPathInfo())) {
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// Create an image, draw the "text" parameter to it and output
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// it to the browser.
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String text = request.getParameter("text");
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BufferedImage bi = new BufferedImage(100, 30,
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BufferedImage.TYPE_3BYTE_BGR);
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bi.getGraphics().drawChars(text.toCharArray(), 0,
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text.length(), 10, 20);
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response.setContentType("image/png");
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ImageIO.write(bi, "png", response.getOutputStream());
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return true;
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}
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// If the URL did not match our image URL, let the other request
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// handlers handle it
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return false;
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}
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};
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@Override
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public void init(VaadinRequest request) {
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Resource resource = new ExternalResource(IMAGE_URL + "?text=Hello!");
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getSession().addRequestHandler(requestHandler);
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// Add an image using the resource
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Image image = new Image("A dynamically generated image", resource);
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setContent(image);
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}
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@Override
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public void detach() {
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super.detach();
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// Clean up
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getSession().removeRequestHandler(requestHandler);
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}
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}
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....
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