1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
---
title: Generating Dynamic Resources Based On URI Or Parameters
order: 28
layout: page
---
[[generating-dynamic-resources-based-on-uri-or-parameters]]
= Generating dynamic resources based on URI or parameters
You can dynamically generate responses based on e.g. query parameters by
creating your own `RequestHandler` and registering it with the session.
In this way, you can for instance create an image that draws a text,
given as a parameter to the image. This has been done in the example
below:
[source,java]
....
public class DynamicImageUI extends UI {
public static final String IMAGE_URL = "myimage.png";
private final RequestHandler requestHandler = new RequestHandler() {
@Override
public boolean handleRequest(VaadinSession session,
VaadinRequest request, VaadinResponse response)
throws IOException {
if (("/" + IMAGE_URL).equals(request.getPathInfo())) {
// Create an image, draw the "text" parameter to it and output
// it to the browser.
String text = request.getParameter("text");
BufferedImage bi = new BufferedImage(100, 30,
BufferedImage.TYPE_3BYTE_BGR);
bi.getGraphics().drawChars(text.toCharArray(), 0,
text.length(), 10, 20);
response.setContentType("image/png");
ImageIO.write(bi, "png", response.getOutputStream());
return true;
}
// If the URL did not match our image URL, let the other request
// handlers handle it
return false;
}
};
@Override
public void init(VaadinRequest request) {
Resource resource = new ExternalResource(IMAGE_URL + "?text=Hello!");
getSession().addRequestHandler(requestHandler);
// Add an image using the resource
Image image = new Image("A dynamically generated image", resource);
setContent(image);
}
@Override
public void detach() {
super.detach();
// Clean up
getSession().removeRequestHandler(requestHandler);
}
}
....
|
