Page History

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Next, all the fields inside the form are activated to pull values out of the incoming request, validate them and (if valid) store the changes.

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_For Tapestry 4 Users:_ Tapestry 5 does not use the fragile "form rewind" approach from Tapestry 4. Instead, a hidden field generated during the render stores the information needed to process the form submission.
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After the fields have done their processing, the Form emits a "validate" event. This is your chance to perform any cross-form validation that can't be described declaratively.

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Storing Data Between Requests

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Starting in Tapestry 5.4, the default behavior for server-side validation failures is to re-render the page within the same request (rather than emitting a redirect). This removes the need to use a session-persistent field to store the validation tracker when validation failures occur.
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As with other action requests, the result of a form submission (except when using Zones) is to send a redirect to the client, which results in a second request (to re-render the page). The ValidationTracker must be persisted (generally in the HttpSession) across these two requests in order to prevent the loss of validation information. Fortunately, the default ValidationTracker provided by the Form component is persistent, so you don't normally have to worry about it.

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package com.example.newapp.pages;


import com.example.newapp.services.UserAuthenticator;
import org.apache.tapestry5.annotations.*;
import org.apache.tapestry5.corelib.components.Form;
import org.apache.tapestry5.corelib.components.PasswordField;
import org.apache.tapestry5.ioc.annotations.Inject;


public class Login {
    @Persist
    @Property 
    private String userName;

    @Property
    private String password;

    @Inject
    private UserAuthenticator authenticator;

    @InjectComponent("password")
    private PasswordField passwordField;

    @Component
    private Form loginForm;

    /**
     * Do the cross-field validation
     */
    void onValidateFromLoginForm() {
        if (!authenticator.isValid(userName, password)) {
            // record an error, and thereby prevent Tapestry from emitting a "success" event
            loginForm.recordError(passwordField, "Invalid user name or password.");
        }
    }

    /**
     * Validation passed, so we'll go to the "PostLogin" page
     */
    Object onSuccess() {
        return PostLogin.class;
    }
}

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Note that the onValidateFromLoginForm() and onSuccess() methods are not public; event handler methods can have any visibility, even private. Package private (that is, no modifier) is the typical use, as it allows the component to be tested, from a test case class in the same package.
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Because a form submission is really two requests: the submission itself (which results in a redirect response), then a second request for the page (which results in a re-rendering of the page), it is necessary to persist the userName field between the two requests, by using the @Persist annotation. This would be necessary for the password field as well, except that the PasswordField component never renders a value.

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Centralizing Validation with @Validate

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