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.ElementType.PARAMETER;
018    import static java.lang.annotation.RetentionPolicy.RUNTIME;
019    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.COMPONENT;
020    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.MIXIN;
021    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.PAGE;
022    
023    import java.lang.annotation.Documented;
024    import java.lang.annotation.Retention;
025    import java.lang.annotation.Target;
026    
027    import org.apache.tapestry5.internal.transform.OnEventWorker;
028    import org.apache.tapestry5.ioc.annotations.UseWith;
029    import org.apache.tapestry5.ioc.services.TypeCoercer;
030    import org.apache.tapestry5.services.Request;
031    
032    /**
033     * Annotation that may be placed on parameters of event handler methods.
034     * Annotated parameters will be {@linkplain Request#getParameter(String) extracted from the request},
035     * then {@linkplain TypeCoercer coerced} to the type of the parameter. Such parameters are separate
036     * from ordinary context parameters (extracted from the Request path). Typically, this is used when
037     * client-side JavaScript adds a query parameter to a request to communicate some information from the client
038     * side to the server side.
039     * <p>
040     * Individual fields may also be directly mapped to query parameters using the {@link ActivationRequestParameter} annotation.
041     * 
042     * @since 5.2.0
043     * @see OnEventWorker
044     */
045    @Target(
046    { PARAMETER })
047    @Retention(RUNTIME)
048    @Documented
049    @UseWith(
050    { COMPONENT, MIXIN, PAGE })
051    public @interface RequestParameter
052    {
053        /** The name of the query parameter to extract from the request. */
054        String value();
055    
056        /**
057         * If false (the default), then an exception is thrown when the query parameter is read, if it is blank (null or an
058         * empty string). If true, then blank values are allowed.
059         */
060        boolean allowBlank() default false;
061    }