001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005// http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.annotations;
014
015import static java.lang.annotation.RetentionPolicy.RUNTIME;
016import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.PAGE;
017
018import java.lang.annotation.Documented;
019import java.lang.annotation.ElementType;
020import java.lang.annotation.Retention;
021import java.lang.annotation.Target;
022
023import org.apache.tapestry5.ComponentResources;
024import org.apache.tapestry5.EventConstants;
025import org.apache.tapestry5.Link;
026import org.apache.tapestry5.ValueEncoder;
027import org.apache.tapestry5.ioc.annotations.UseWith;
028import org.apache.tapestry5.services.ValueEncoderSource;
029
030/**
031 * Marks a field of a page (not a component) as persistent within the URL, as with a page activation context. The field
032 * is mapped
033 * to a query parameter. When component event or page render links are generated for the page,
034 * additional values will be added to the {@link Link} (via the {@link EventConstants#DECORATE_COMPONENT_EVENT_LINK} or
035 * {@link EventConstants#DECORATE_PAGE_RENDER_LINK} events).
036 * <p>
037 * The field may be of any type; a {@link ValueEncoder} (from the {@link ValueEncoderSource}) will be used to convert
038 * between client-side and server-side representations. Null values are not added as query parameters (just non-null).
039 * <p>
040 * When a page is activated, the mapped fields will receive their values before an {@linkplain EventConstants#ACTIVATE
041 * activate} event handler method is invoked.
042 * <p>
043 * This annotation is an alternative to {@link Persist}.
044 * <p>
045 * Fields annotated with ActivationRequestParameter are <em>not</em> considered persistent (its a process parallel to the one
046 * related to the {@link Persist} annotation). Invoking {@link ComponentResources#discardPersistentFieldChanges()} will
047 * <em>not</em> affect annotated fields, only assigning them back to null will.
048 *
049 * @see RequestParameter
050 * @see ValueEncoder
051 */
052@Target(
053{ ElementType.FIELD })
054@Retention(RUNTIME)
055@Documented
056@UseWith(
057{ PAGE })
058public @interface ActivationRequestParameter
059{
060    /** The name of the query parameter, which defaults to the name of the field. */
061    String value() default "";
062
063    /**
064     * If true then a null value is an error. If false, then a null value will result in no update to the field. Either way,
065     * a null field value will result in no query parameter added to a  {@linkplain org.apache.tapestry5.Link generated link}.
066     *
067     * @since 5.4
068     */
069    boolean required() default false;
070}