io.druid.java.util.common.CloseableIterators.java Source code

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Here is the source code for io.druid.java.util.common.CloseableIterators.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.java.util.common;

import com.google.common.base.Preconditions;
import com.google.common.collect.Iterators;
import io.druid.java.util.common.io.Closer;
import io.druid.java.util.common.parsers.CloseableIterator;

import javax.annotation.Nullable;
import java.io.Closeable;
import java.io.IOException;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

public class CloseableIterators {
    public static <T> CloseableIterator<T> concat(List<? extends CloseableIterator<? extends T>> iterators) {
        final Closer closer = Closer.create();
        iterators.forEach(closer::register);

        final Iterator<T> innerIterator = Iterators.concat(iterators.iterator());
        return wrap(innerIterator, closer);
    }

    public static <T> CloseableIterator<T> mergeSorted(List<? extends CloseableIterator<? extends T>> iterators,
            Comparator<T> comparator) {
        Preconditions.checkNotNull(comparator);

        final Closer closer = Closer.create();
        iterators.forEach(closer::register);

        final Iterator<T> innerIterator = Iterators.mergeSorted(iterators, comparator);
        return wrap(innerIterator, closer);
    }

    public static <T> CloseableIterator<T> wrap(Iterator<T> innerIterator, @Nullable Closeable closeable) {
        return new CloseableIterator<T>() {
            private boolean closed;

            @Override
            public boolean hasNext() {
                return innerIterator.hasNext();
            }

            @Override
            public T next() {
                return innerIterator.next();
            }

            @Override
            public void close() throws IOException {
                if (!closed) {
                    if (closeable != null) {
                        closeable.close();
                    }
                    closed = true;
                }
            }
        };
    }

    public static <T> CloseableIterator<T> withEmptyBaggage(Iterator<T> innerIterator) {
        return wrap(innerIterator, null);
    }

    private CloseableIterators() {
    }
}