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
015package org.apache.tapestry5.annotations;
016
017import org.apache.tapestry5.EventConstants;
018import org.apache.tapestry5.ioc.annotations.UseWith;
019import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
020
021import java.lang.annotation.Documented;
022import java.lang.annotation.ElementType;
023import java.lang.annotation.Retention;
024import static java.lang.annotation.RetentionPolicy.RUNTIME;
025import 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})
052public @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}