001    // Copyright 2006, 2007, 2008 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.tapestry.annotations;
016    
017    import org.apache.tapestry.TapestryConstants;
018    
019    import java.lang.annotation.Documented;
020    import java.lang.annotation.ElementType;
021    import java.lang.annotation.Retention;
022    import static java.lang.annotation.RetentionPolicy.RUNTIME;
023    import java.lang.annotation.Target;
024    
025    /**
026     * Marks a method as a handler for a client side event. The handler method will be invoked when a component triggers an
027     * event. Filters on the type of event and on the originating component ensure that only the appropriate methods are
028     * invoked.
029     * <p/>
030     * Client events include a <em>context</em> of one or more values. These context values are included in the action URI.
031     * The values are optionally supplied to the handler method as parameters. Automatic {@linkplain
032     * org.apache.tapestry.ValueEncoder conversion} from string to the type of the actual parameter occur.
033     * <p/>
034     * Handlers may return a value. Returning a non-null value will abort the handling of the event, and will usually
035     * control the response sent to the client web browser. The details are somewhat specific to the type of event and the
036     * component involved.
037     * <p/>
038     * If a handler is not found within the originating component (or no handler aborts the event handling), then handlers
039     * within the containing component will be searched. This continues up the page hierarchy. In some cases, having no
040     * handlers (or no aborting handlers) is considered acceptible; in others, it is an error. Again, this is defined by the
041     * type of originating component, and the type of event.
042     * <p/>
043     * <strong>If you fail to provide filters on either component or event type, then your method will be invoked for all
044     * component events, possibly including events that bubble up from embedded sub-components. </strong>
045     */
046    @Target(ElementType.METHOD)
047    @Retention(RUNTIME)
048    @Documented
049    public @interface OnEvent
050    {
051    
052        /**
053         * The event type to match. The handler will only be invoked if the client event type matches the value. The default
054         * value is "action".  Matching is case-insensitive.
055         */
056        String value() default TapestryConstants.ACTION_EVENT;
057    
058        /**
059         * The local id of the component from which the event originates. If not specified, then the default is to match any
060         * component. If an event from a component is not handled in the component's container, it is re-triggered inside
061         * the component's grand-container and will appear to originate from the container. Thus events that escape a
062         * component will appear to originate in the component's container, and so forth.
063         * <p/>
064         * <p/>
065         * Matching by component id is case insensitive.
066         */
067        String component() default "";
068    
069    }