    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 org.apache.tapestry5.EventConstants;
    016import org.apache.tapestry5.ioc.annotations.UseWith;
    017
    018import java.lang.annotation.Documented;
    019import java.lang.annotation.ElementType;
    020import java.lang.annotation.Retention;
    021import java.lang.annotation.Target;
    022
    023import static java.lang.annotation.RetentionPolicy.RUNTIME;
    024import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    025
    026/**
    027 * Marks a method as a handler for a client side event. The handler method will be invoked when a component triggers an
    028 * event. Filters on the type of event and on the originating component ensure that only the appropriate methods are
    029 * invoked.
    030 *
    031 * Client events include a <em>context</em> of one or more values. These context values are included in the action URI.
    032 * The values are optionally supplied to the handler method as parameters. Automatic {@linkplain
    033 * org.apache.tapestry5.ValueEncoder conversion} from string to the type of the actual parameter occur.
    034 *
    035 * Handlers may return a value. Returning a non-null value will abort the handling of the event, and will usually
    036 * control the response sent to the client web browser. The details are somewhat specific to the type of event and the
    037 * component involved.
    038 *
    039 * If a handler is not found within the originating component (or no handler aborts the event handling), then handlers
    040 * within the containing component will be searched. This continues up the page hierarchy. In some cases, having no
    041 * handlers (or no aborting handlers) is considered acceptible; in others, it is an error. Again, this is defined by the
    042 * type of originating component, and the type of event.
    043 *
    044 * <strong>If you fail to provide filters on either component or event type, then your method will be invoked for all
    045 * component events, possibly including events that bubble up from embedded sub-components. </strong>
    046 */
    047@Target(ElementType.METHOD)
    048@Retention(RUNTIME)
    049@Documented
    050@UseWith({COMPONENT,MIXIN,PAGE})
    051public @interface OnEvent
    052{
    053
    054    /**
    055     * The event type to match. The handler will only be invoked if the client event type matches the value. The default
    056     * value is "action".  Matching is case-insensitive.
    057     *
    058     * @see org.apache.tapestry5.EventConstants
    059     */
    060    String value() default EventConstants.ACTION;
    061
    062    /**
    063     * The local id of the component from which the event originates. If not specified, then the default is to match any
    064     * component. If an event from a component is not handled in the component's container, it is re-triggered inside
    065     * the component's grand-container and will appear to originate from the container. Thus events that escape a
    066     * component will appear to originate in the component's container, and so forth.
    067     *
    068     * Matching by component id is case insensitive.
    069     */
    070    String component() default "";
    071}