com.github.jknack.handlebars.io.CompositeTemplateLoader.java Source code

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Here is the source code for com.github.jknack.handlebars.io.CompositeTemplateLoader.java

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/**
 * Copyright (c) 2012-2013 Edgar Espina
 *
 * This file is part of Handlebars.java.
 *
 * 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 com.github.jknack.handlebars.io;

import static org.apache.commons.lang3.Validate.isTrue;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * Combine two or more {@link TemplateLoader} as a single {@link TemplateLoader}.
 * {@link TemplateLoader}s are executed in the order they are provided.
 * </p>
 * <p>
 * Execution is as follows:
 * </p>
 * <ul>
 * <li>If a {@link TemplateLoader} is able to resolve a {@link TemplateSource}, that
 * {@link TemplateSource} is considered the response.</li>
 * <li>If a {@link TemplateLoader} throws a {@link IOException} exception the next
 * {@link TemplateLoader} in the chain will be used.</li>
 * </ul>
 *
 * @author edgar.espina
 * @since 1.0.0
 */
public class CompositeTemplateLoader implements TemplateLoader {

    /**
     * The logging system.
     */
    private static final Logger logger = LoggerFactory.getLogger(CompositeTemplateLoader.class);

    /**
     * The template loader list.
     */
    private final TemplateLoader[] delegates;

    /**
     * Creates a new {@link CompositeTemplateLoader}.
     *
     * @param loaders The template loader chain. At least two loaders must be provided.
     */
    public CompositeTemplateLoader(final TemplateLoader... loaders) {
        isTrue(loaders.length > 1, "At least two loaders are required.");
        this.delegates = loaders;
    }

    @Override
    public TemplateSource sourceAt(final String location) throws IOException {
        for (TemplateLoader delegate : delegates) {
            try {
                return delegate.sourceAt(location);
            } catch (IOException ex) {
                // try next loader in the chain.
                logger.trace("Unable to resolve: {}, trying next loader in the chain.", location);
            }
        }
        throw new FileNotFoundException(location);
    }

    @Override
    public String resolve(final String location) {
        for (TemplateLoader delegate : delegates) {
            try {
                delegate.sourceAt(location);
                return delegate.resolve(location);
            } catch (IOException ex) {
                // try next loader in the chain.
                logger.trace("Unable to resolve: {}, trying next loader in the chain.", location);
            }
        }
        throw new IllegalStateException("Can't resolve: '" + location + "'");
    }

    @Override
    public String getPrefix() {
        throw new UnsupportedOperationException();
    }

    @Override
    public String getSuffix() {
        throw new UnsupportedOperationException();
    }

    @Override
    public void setPrefix(final String prefix) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void setSuffix(final String suffix) {
        throw new UnsupportedOperationException();
    }

    /**
     * Returns the delegates template loaders.
     *
     * @return The delegates template loaders.
     */
    public Iterable<TemplateLoader> getDelegates() {
        return Arrays.asList(delegates);
    }
}