    001    // Copyright 2006 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.internal.bindings;
    016
    017    import org.apache.tapestry5.Binding;
    018    import org.apache.tapestry5.ioc.BaseLocatable;
    019    import org.apache.tapestry5.ioc.Location;
    020    import org.apache.tapestry5.ioc.internal.util.TapestryException;
    021
    022    import java.lang.annotation.Annotation;
    023
    024    /**
    025     * Abstract base class for bindings. Assumes that the binding is read only and invariant. Subclasses must provide an
    026     * implementation of {@link Binding#get()}.
    027     */
    028    public abstract class AbstractBinding extends BaseLocatable implements Binding
    029    {
    030        public AbstractBinding()
    031        {
    032            this(null);
    033        }
    034
    035        protected AbstractBinding(Location location)
    036        {
    037            super(location);
    038        }
    039
    040        /**
    041         * @throws TapestryException always
    042         */
    043        public void set(Object value)
    044        {
    045            throw new TapestryException(BindingsMessages.bindingIsReadOnly(this), this, null);
    046        }
    047
    048        /**
    049         * Returns true. Subclasses that do not supply a fixed, read-only value should override this method to return
    050         * false.
    051         */
    052        public boolean isInvariant()
    053        {
    054            return true;
    055        }
    056
    057        /**
    058         * Returns the actual class, by invoking {@link Binding#get()}. Subclasses may override this method to work more
    059         * efficiently (say, when the binding type is known statically).
    060         */
    061        public Class getBindingType()
    062        {
    063            return get().getClass();
    064        }
    065
    066        /**
    067         * Always returns null. Bindings that provide access to a method or field will override this method to return the
    068         * appropriate annotation.
    069         */
    070        public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
    071        {
    072            return null;
    073        }
    074
    075    }