io.druid.data.input.impl.AbstractTextFilesFirehoseFactory.java Source code

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Here is the source code for io.druid.data.input.impl.AbstractTextFilesFirehoseFactory.java

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/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets licenses this file
 * to you 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 io.druid.data.input.impl;

import com.google.common.base.Preconditions;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import io.druid.data.input.Firehose;
import io.druid.data.input.FirehoseFactory;
import io.druid.java.util.common.logger.Logger;
import org.apache.commons.io.Charsets;
import org.apache.commons.io.IOUtils;
import org.apache.commons.io.LineIterator;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * This is an abstract class for firehose factory for making firehoses reading text files.
 * It provides an unified {@link #connect(StringInputRowParser, File)} implementation for its subclasses.
 *
 * @param <T> object type representing input data
 */
public abstract class AbstractTextFilesFirehoseFactory<T> implements FirehoseFactory<StringInputRowParser> {
    private static final Logger LOG = new Logger(AbstractTextFilesFirehoseFactory.class);

    private List<T> objects;

    @Override
    public Firehose connect(StringInputRowParser firehoseParser, File temporaryDirectory) throws IOException {
        if (objects == null) {
            objects = ImmutableList.copyOf(Preconditions.checkNotNull(initObjects(), "initObjects"));
        }
        final Iterator<T> iterator = objects.iterator();
        return new FileIteratingFirehose(new Iterator<LineIterator>() {
            @Override
            public boolean hasNext() {
                return iterator.hasNext();
            }

            @Override
            public LineIterator next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }
                final T object = iterator.next();
                try {
                    return IOUtils.lineIterator(wrapObjectStream(object, openObjectStream(object)), Charsets.UTF_8);
                } catch (Exception e) {
                    LOG.error(e, "Exception reading object[%s]", object);
                    throw Throwables.propagate(e);
                }
            }
        }, firehoseParser);
    }

    /**
     * Initialize objects to be read by this firehose.  Since firehose factories are constructed whenever
     * io.druid.indexing.common.task.Task objects are deserialized, actual initialization of objects is deferred
     * until {@link #connect(StringInputRowParser, File)} is called.
     *
     * @return a collection of initialized objects.
     */
    protected abstract Collection<T> initObjects() throws IOException;

    /**
     * Open an input stream from the given object.  If the object is compressed, this method should return a byte stream
     * as it is compressed.  The object compression should be handled in {@link #wrapObjectStream(Object, InputStream)}.
     *
     * @param object an object to be read
     *
     * @return an input stream for the object
     *
     * @throws IOException
     */
    protected abstract InputStream openObjectStream(T object) throws IOException;

    /**
     * Wrap the given input stream if needed.  The decompression logic should be applied to the given stream if the object
     * is compressed.
     *
     * @param object an input object
     * @param stream a stream for the object
     * @return
     * @throws IOException
     */
    protected abstract InputStream wrapObjectStream(T object, InputStream stream) throws IOException;
}