de.cosmocode.rendering.DefaultListRenderer.java Source code

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Here is the source code for de.cosmocode.rendering.DefaultListRenderer.java

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/**
 * Copyright 2010 CosmoCode GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package de.cosmocode.rendering;

import java.util.List;

import com.google.common.base.Preconditions;

/**
 * A decorator for {@link Renderer} which assumes
 * the constructed object is a {@link List}.
 *
 * @author Willi Schoenborn
 */
public final class DefaultListRenderer extends ForwardingRenderer implements ListRenderer {

    private final Renderer renderer;

    public DefaultListRenderer(Renderer renderer) {
        this.renderer = Preconditions.checkNotNull(renderer, "Renderer");
    }

    @Override
    protected Renderer delegate() {
        return renderer;
    }

    @SuppressWarnings("unchecked")
    private List<Object> cast(Object list) {
        return List.class.cast(list);
    }

    @Override
    public List<Object> build() throws RenderingException {
        final Object list = super.build();
        Preconditions.checkState(list instanceof List<?>, "Expected list, but was %s", list);
        return cast(list);
    }

}