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
015package org.apache.tapestry5.internal.bindings;
016
017import org.apache.tapestry5.Binding;
018import org.apache.tapestry5.ioc.BaseLocatable;
019import org.apache.tapestry5.ioc.Location;
020import org.apache.tapestry5.ioc.internal.util.TapestryException;
021
022import 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 */
028public 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}