    001// Copyright 2006, 2011 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.Binding2;
    019import org.apache.tapestry5.ioc.BaseLocatable;
    020import org.apache.tapestry5.ioc.Location;
    021import org.apache.tapestry5.ioc.internal.util.TapestryException;
    022
    023import java.lang.annotation.Annotation;
    024import java.lang.reflect.Type;
    025
    026/**
    027 * Abstract base class for bindings. Assumes that the binding is read only and invariant. Subclasses must provide an
    028 * implementation of {@link Binding#get()}.
    029 */
    030public abstract class AbstractBinding extends BaseLocatable implements Binding2
    031{
    032    public AbstractBinding()
    033    {
    034        this(null);
    035    }
    036
    037    protected AbstractBinding(Location location)
    038    {
    039        super(location);
    040    }
    041
    042    /**
    043     * @throws TapestryException always
    044     */
    045    public void set(Object value)
    046    {
    047        throw new TapestryException(String.format("Binding %s is read-only.", this), this, null);
    048    }
    049
    050    /**
    051     * Returns true. Subclasses that do not supply a fixed, read-only value should override this method to return
    052     * false.
    053     */
    054    public boolean isInvariant()
    055    {
    056        return true;
    057    }
    058
    059    /**
    060     * Returns the actual class, by invoking {@link Binding#get()}. Subclasses may override this method to work more
    061     * efficiently (say, when the binding type is known statically).
    062     */
    063    public Class getBindingType()
    064    {
    065        return get().getClass();
    066    }
    067
    068    /**
    069     * Passes straight through to {@link AbstractBinding#getBindingType()}. Subclasses may override this method to
    070     * return the generic type if it is available
    071     */
    072    public Type getBindingGenericType()
    073    {
    074        return getBindingType();
    075    }
    076
    077    /**
    078     * Always returns null. Bindings that provide access to a method or field will override this method to return the
    079     * appropriate annotation.
    080     */
    081    public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
    082    {
    083        return null;
    084    }
    085
    086}