...
This dichotomy between component event requests and render requests alleviates a number of problems in traditional web applications related to the browser back button, or to the user hitting the refresh button in their browser.
Contents
Table of Contents | ||
---|---|---|
|
Logical Page Name Shortening
In certain cases, Tapestry will shorten the the logical name of a page. For example, the page class org.example.pages.address.CreateAddress will be given a logical name of "address/Create" (the redundant "Address" is removed as a suffix). However, this only affects how the page is referenced in URLs; the template file will still be CreateAddress.tml, whether on the classpath, or as address/CreateAddress.tml (in the web context).
...
Component Event Requests & Responses
Main Article: Component Events
Component event requests may take the form of hyperlinks (EventLink or ActionLink) or form submissions (Form).
...
The URL for a component event request identifies the name of the page, the nested id of the component, and the name of the event to trigger on the component (this is usually specified by the "event" parameter of EventLink, or "action" for an ActionLink). Further, a component event request may contain additional context information, which will be provided to the event handler method.
...
If the event handler method returns no value, or returns null, then the current page (the page containing the component) will render the response.
A page render link URL for the current page is created and sent to the client as a client side redirect. The client browser will automatically submit a new request to generate the page.
...
An event handler method may return a an instance of HttpError instance to send an error response to the client.
...
An event handler can also return a StreamResponse object, which encapsulates a stream to be sent directly to the client browser. This is useful for components that want to, say, generate an image or PDF and provide it to the client.
8. URL response
:
Code Block |
---|
public Object onAction(){
return new StreamResponse() {
@Override
public String getContentType() {
return "application/pdf";
}
@Override
public InputStream getStream() throws IOException {
return new ByteArrayInputStream(getMyPdfByteArray());
}
@Override
public void prepareResponse(Response response) {
response.setHeader("Content-Disposition", "attachment; filename=\"" + myFileName + "\"");
}
};
} |
8. URL response
A java.net.URL response is A java.net.URL response is handled as a client redirect to an external URL. (In Tapestry 5.3.x and earlier this only works for non-Ajax requests.)
...
Render requests are simpler in structure and behavior than component event requests. In the simplest case, the URL is simply the logical name of the page.
Pages may have an activation context. The activation context represents persistent information about the state of the page. In practical terms, the activation context is usually the id of some database-persistent object.
When a page has an activation context, the values of the context are appended to the URL path.
is simply the logical name of the page.
Pages may have an activation context. The activation context represents persistent information about the state of the page. In practical terms, the activation context is usually the id of some database-persistent object.
When a page has an activation context, the values of the context are appended to the URL path. For example, in http://www.example.com/myapp/foo/bar
the "myapp" part is the servlet context (usually the name of your app), and the "foo/bar" part is the activation context, with "foo" being the first activation parameter and "bar" being the second.
It is common for most pages to not have any Not all pages have an activation context.
The activation context may be explicitly set when the render request link is created (the PageLink component has a context parameter for this purpose).
When no explicit activation context is provided, the page itself is queried for its activation context. This querying takes the form of an event trigger. The event name is "passivate" (as we'll see shortly, there's a corresponding "activate"). The return value of the method is used as the context. For example:
Code Block | ||||
---|---|---|---|---|
| ||||
public class ProductDetail { private Product product; . . . long onPassivate() { return product.getId(); } } |
...
Info |
---|
Note: If you are using the tapestry-hibernate integration library and your passivate context is a Hibernate entity, then you can just use the entity itself, not its id. Tapestry will automatically extract the entity's id into the URL, and convert it back for the "activate" event handler method. |
Page
...
Activation
When a page render request arrives, the page is activated before it is rendered.
Wiki Markup |
---|
{float:right|background=#eee|padding=0 1em}
*JumpStart Demos:*
[onActivate and onPassivate| |
...
https://tapestry-jumpstart. |
...
org/jumpstart/examples/navigation/onactivateandonpassivate/3] [Handling A Bad Context| |
...
https://tapestry-jumpstart. |
...
org/jumpstart/examples/infrastructure/handlingabadcontext/1] {float} |
Activation serves two purposes:
...
Page activation uses Tapestry's Component Event mechanism. See See Component Events for details.
A page's activate event handler mirrors its passivate handler:
Code Block | ||||
---|---|---|---|---|
| ||||
private Product product; . . . void onActivate(long productId) { product = productDAO.getById(productId); } . . . |
Here's the relevant part: when the page renders, it is likely to include more component event request URLs (links and forms). The component event requests for those links and forms will also start by activating the page, before performing other work. This forms an unbroken chain of requests that include the same activation context.
To some degree, this same effect could be accomplished using a persistent page value, but that requires an active servlet session, and the result is not bookmarkable.
The Your activate event handler, like any event handler, may also return a value, which is treated identically to a return value of a component event method. This will typically be used in an technique is commonly used as a simple access validation scenariomechanism.
It is common to You sometimes need to handle multiple page activation scenarios in one page class. You can could create multiple activate event handler methods with different arguments (see the "Multiple Method Matches" section at at Component Events for details), but if you do so, you should generally return true
from each to avoid having more than one activation event handler method from being called for each page request. However, a better approach is to create one method with an EventContext argument. Tapestry will populate the EventContext argument with all of the activation parameters, and the EventContext's get
method will retrieve and coerce each parameter to the desired type. For example:
Code Block | ||||
---|---|---|---|---|
| ||||
. . . void onActivate(EventContext eventContext) { String color = DEFAULT_COLOR; if (eventContext.getCount() > 0) { long productId = eventContext.get(Long.class, 0); if (eventContext.getCount() > 1) { String color = eventContext.get(String.class, 1); } product = productDAO.getById(productId, color); } else { return SelectProduct.class; // no product selected } } . . . |
Page Navigation Patterns
...
At some point, persistent values make more sense. Tapestry has several persistence strategies available, including one that stores data in URL query parameters. See See Persistent Page Data for details.
Scrollbar |
---|