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    }