    001    // Copyright 2010 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.annotations;
    016
    017    import static java.lang.annotation.RetentionPolicy.RUNTIME;
    018    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.PAGE;
    019
    020    import java.lang.annotation.Documented;
    021    import java.lang.annotation.ElementType;
    022    import java.lang.annotation.Retention;
    023    import java.lang.annotation.Target;
    024
    025    import org.apache.tapestry5.ComponentResources;
    026    import org.apache.tapestry5.EventConstants;
    027    import org.apache.tapestry5.Link;
    028    import org.apache.tapestry5.ValueEncoder;
    029    import org.apache.tapestry5.ioc.annotations.UseWith;
    030    import org.apache.tapestry5.services.ValueEncoderSource;
    031
    032    /**
    033     * Marks a field of a page (not a component) as persistent within the URL, as with a page activation context. The field
    034     * is mapped
    035     * to a query parameter. When component event or page render links are generated for the page,
    036     * additional values will be added to the {@link Link} (via the {@link EventConstants#DECORATE_COMPONENT_EVENT_LINK} or
    037     * {@link EventConstants#DECORATE_PAGE_RENDER_LINK} events).
    038     * <p>
    039     * The field may be of any type; a {@link ValueEncoder} (from the {@link ValueEncoderSource}) will be used to convert
    040     * between client-side and server-side representations. Null values are not added as query parameters (just non-null).
    041     * <p>
    042     * When a page is activated, the mapped fields will receive their values before an {@linkplain EventConstants#ACTIVATE
    043     * activate} event handler method is invoked.
    044     * <p>
    045     * This annotation is an alternative to {@link Persist}.
    046     * <p>
    047     * Fields annotated with ActivationRequestParameter are <em>not</em> considered persistent (its a process parallel to the one
    048     * related to the {@link Persist} annotation). Invoking {@link ComponentResources#discardPersistentFieldChanges()} will
    049     * <em>not</em> affect annotated fields, only assigning them back to null will.
    050     *
    051     * @see RequestParameter
    052     */
    053    @Target(
    054    { ElementType.FIELD })
    055    @Retention(RUNTIME)
    056    @Documented
    057    @UseWith(
    058    { PAGE })
    059    public @interface ActivationRequestParameter
    060    {
    061        /** The name of the query parameter, which defaults to the name of the field. */
    062        String value() default "";
    063
    064        // TODO: Attributes to limit it to just render links, or just component event links?
    065    }