wayang-commons/wayang-core/src/main/java/org/apache/wayang/core/util/fs/FileUtils.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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 org.apache.wayang.core.util.fs;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UncheckedIOException;
import java.util.Iterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import org.apache.commons.io.IOUtils;
import org.apache.wayang.core.api.exception.WayangException;

public class FileUtils {

    /**
     * Creates a {@link Stream} of a lines of the file.
     *
     * @param path of the file
     * @return the {@link Stream}
     */
    public static Stream<String> streamLines(String path) {
        final FileSystem fileSystem = FileSystems.getFileSystem(path).orElseThrow(
                () -> new IllegalStateException(String.format("No file system found for %s", path))
        );
        try {
            Iterator<String> lineIterator = createLineIterator(fileSystem, path);
            return StreamSupport.stream(Spliterators.spliteratorUnknownSize(lineIterator, 0), false);
        } catch (IOException e) {
            throw new WayangException(String.format("%s failed to read %s.", FileUtils.class, path), e);
        }

    }

    /**
     * Creates an {@link Iterator} over the lines of a given {@code path} (that resides in the given {@code fileSystem}).
     */
    private static Iterator<String> createLineIterator(FileSystem fileSystem, String path) throws IOException {
        final BufferedReader reader = new BufferedReader(new InputStreamReader(fileSystem.open(path), "UTF-8"));
        return new Iterator<String>() {

            String next;

            {
                this.advance();
            }

            private void advance() {
                try {
                    this.next = reader.readLine();
                } catch (IOException e) {
                    this.next = null;
                    throw new UncheckedIOException(e);
                } finally {
                    if (this.next == null) {
                        IOUtils.closeQuietly(reader);
                    }
                }
            }

            @Override
            public boolean hasNext() {
                return this.next != null;
            }

            @Override
            public String next() {
                assert this.hasNext();
                final String returnValue = this.next;
                this.advance();
                return returnValue;
            }
        };
    }
}