net.middell.combo.TextResourceCombo.java Source code

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Here is the source code for net.middell.combo.TextResourceCombo.java

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/*
 * #%L
 * Text Resource Combo Utilities
 * %%
 * Copyright (C) 2012 Gregor Middell
 * %%
 * 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.
 * #L%
 */
package net.middell.combo;

import com.google.common.collect.Iterables;
import com.google.common.io.CharStreams;
import com.google.common.io.InputSupplier;

import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;

/**
 * An ordered sequential combination of text-based resources.
 * <p/>
 * Serves as a container for resources, exposes aggregated metadata and is usable as an input supplier of the joint
 * contents in the contained resources.
 *
 * @author <a href="http://gregor.middell.net/" title="Homepage">Gregor Middell</a>
 */
public class TextResourceCombo extends ArrayList<TextResource> implements InputSupplier<Reader> {

    /**
     * Constructor.
     *
     * @param resources the resources to be contained in this combo. The iteration order of the parameter is
     *                  supposed to be significant.
     */
    public TextResourceCombo(Iterable<TextResource> resources) {
        super(Iterables.size(resources));
        Iterables.addAll(this, resources);
    }

    /**
     * Determines the media type of this combo by retrieving it from the first member.
     *
     * @return the media type or <code>text/plain</code> in the case of an empty combo
     */
    public String getMediaType() {
        return (isEmpty() ? TextResource.TEXT_PLAIN : get(0).getMediaType());
    }

    /**
     * Determines the latest modification time of all contained resources.
     *
     * @return the latest modification time
     * @see java.io.File#lastModified()
     */
    public long lastModified() {
        long lastModified = 0;
        for (TextResource rd : this) {
            lastModified = Math.max(lastModified, rd.lastModified);
        }
        return (lastModified > 0 ? lastModified : System.currentTimeMillis());
    }

    /**
     * Determines the smallest maximum cache age of all contained resources.
     *
     * @return the maximum cache age of this combo (in seconds)
     */
    public long maxAge() {
        long maxAge = Long.MAX_VALUE;
        for (TextResource rd : this) {
            maxAge = Math.min(maxAge, rd.maxAge);
        }
        return (maxAge < Long.MAX_VALUE ? maxAge : 0);
    }

    /**
     * Provides a joint reader of all contained resources in their given order.
     *
     * @return a reader concatenating the contents of all resources in the combo
     * @throws IOException
     */
    @Override
    public Reader getInput() throws IOException {
        return CharStreams.join(this).getInput();
    }
}