    001    // Copyright 2006, 2007, 2008, 2009 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 org.apache.tapestry5.EventConstants;
    018    import org.apache.tapestry5.ioc.annotations.UseWith;
    019    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    020
    021    import java.lang.annotation.Documented;
    022    import java.lang.annotation.ElementType;
    023    import java.lang.annotation.Retention;
    024    import static java.lang.annotation.RetentionPolicy.RUNTIME;
    025    import java.lang.annotation.Target;
    026
    027    /**
    028     * Marks a method as a handler for a client side event. The handler method will be invoked when a component triggers an
    029     * event. Filters on the type of event and on the originating component ensure that only the appropriate methods are
    030     * invoked.
    031     * <p/>
    032     * Client events include a <em>context</em> of one or more values. These context values are included in the action URI.
    033     * The values are optionally supplied to the handler method as parameters. Automatic {@linkplain
    034     * org.apache.tapestry5.ValueEncoder conversion} from string to the type of the actual parameter occur.
    035     * <p/>
    036     * Handlers may return a value. Returning a non-null value will abort the handling of the event, and will usually
    037     * control the response sent to the client web browser. The details are somewhat specific to the type of event and the
    038     * component involved.
    039     * <p/>
    040     * If a handler is not found within the originating component (or no handler aborts the event handling), then handlers
    041     * within the containing component will be searched. This continues up the page hierarchy. In some cases, having no
    042     * handlers (or no aborting handlers) is considered acceptible; in others, it is an error. Again, this is defined by the
    043     * type of originating component, and the type of event.
    044     * <p/>
    045     * <strong>If you fail to provide filters on either component or event type, then your method will be invoked for all
    046     * component events, possibly including events that bubble up from embedded sub-components. </strong>
    047     */
    048    @Target(ElementType.METHOD)
    049    @Retention(RUNTIME)
    050    @Documented
    051    @UseWith({COMPONENT,MIXIN,PAGE})
    052    public @interface OnEvent
    053    {
    054
    055        /**
    056         * The event type to match. The handler will only be invoked if the client event type matches the value. The default
    057         * value is "action".  Matching is case-insensitive.
    058         *
    059         * @see org.apache.tapestry5.EventConstants
    060         */
    061        String value() default EventConstants.ACTION;
    062
    063        /**
    064         * The local id of the component from which the event originates. If not specified, then the default is to match any
    065         * component. If an event from a component is not handled in the component's container, it is re-triggered inside
    066         * the component's grand-container and will appear to originate from the container. Thus events that escape a
    067         * component will appear to originate in the component's container, and so forth.
    068         * <p/>
    069         * Matching by component id is case insensitive.
    070         */
    071        String component() default "";
    072    }