001    // Copyright 2006, 2009, 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.FIELD;
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.ioc.annotations.UseWith;
028    import org.apache.tapestry5.services.javascript.JavaScriptSupport;
029    
030    /**
031     * Defines a field of a component class that is replaced at runtime with a read-only value obtained from the
032     * {@link org.apache.tapestry5.services.Environment} service.
033     * <p>
034     * Most commonly, the field will be of type {@link JavaScriptSupport}, {@link org.apache.tapestry5.services.Heartbeat}
035     * or {@link org.apache.tapestry5.services.FormSupport}, though many other options are possible.
036     */
037    @Target(FIELD)
038    @Documented
039    @Retention(RUNTIME)
040    @UseWith(
041    { COMPONENT, MIXIN, PAGE })
042    public @interface Environmental
043    {
044        /**
045         * The value determines if the environmental service to be injected is required or not. In most cases, it is, so the
046         * default is true.
047         */
048        boolean value() default true;
049    }