org.apache.calcite.adapter.csv.CsvStreamReader.java Source code

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Here is the source code for org.apache.calcite.adapter.csv.CsvStreamReader.java

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/*
 * 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.calcite.adapter.csv;

import org.apache.calcite.util.Source;

import org.apache.commons.io.input.Tailer;
import org.apache.commons.io.input.TailerListener;
import org.apache.commons.io.input.TailerListenerAdapter;

import au.com.bytecode.opencsv.CSVParser;
import au.com.bytecode.opencsv.CSVReader;

import java.io.Closeable;
import java.io.IOException;
import java.io.StringReader;
import java.util.ArrayDeque;
import java.util.Queue;

/**
 * Extension to {@link CSVReader} that can read newly appended file content.
 */
class CsvStreamReader extends CSVReader implements Closeable {
    protected CSVParser parser;
    protected int skipLines;
    protected Tailer tailer;
    protected Queue<String> contentQueue;

    /**
     * The default line to start reading.
     */
    public static final int DEFAULT_SKIP_LINES = 0;

    /**
     * The default file monitor delay.
     */
    public static final long DEFAULT_MONITOR_DELAY = 2000;

    CsvStreamReader(Source source) {
        this(source, CSVParser.DEFAULT_SEPARATOR, CSVParser.DEFAULT_QUOTE_CHARACTER,
                CSVParser.DEFAULT_ESCAPE_CHARACTER, DEFAULT_SKIP_LINES, CSVParser.DEFAULT_STRICT_QUOTES,
                CSVParser.DEFAULT_IGNORE_LEADING_WHITESPACE);
    }

    /**
     * Creates a CsvStreamReader with supplied separator and quote char.
     *
     * @param source The file to an underlying CSV source
     * @param separator The delimiter to use for separating entries
     * @param quoteChar The character to use for quoted elements
     * @param escape The character to use for escaping a separator or quote
     * @param line The line number to skip for start reading
     * @param strictQuotes Sets if characters outside the quotes are ignored
     * @param ignoreLeadingWhiteSpace If true, parser should ignore
     *  white space before a quote in a field
     */
    private CsvStreamReader(Source source, char separator, char quoteChar, char escape, int line,
            boolean strictQuotes, boolean ignoreLeadingWhiteSpace) {
        super(new StringReader("")); // dummy call to base constructor
        contentQueue = new ArrayDeque<>();
        TailerListener listener = new CsvContentListener(contentQueue);
        tailer = Tailer.create(source.file(), listener, DEFAULT_MONITOR_DELAY, false, true, 4096);
        this.parser = new CSVParser(separator, quoteChar, escape, strictQuotes, ignoreLeadingWhiteSpace);
        this.skipLines = line;
        try {
            // wait for tailer to capture data
            Thread.sleep(DEFAULT_MONITOR_DELAY);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Reads the next line from the buffer and converts to a string array.
     *
     * @return a string array with each comma-separated element as a separate entry.
     *
     * @throws IOException if bad things happen during the read
     */
    public String[] readNext() throws IOException {
        String[] result = null;
        do {
            String nextLine = getNextLine();
            if (nextLine == null) {
                return null;
            }
            String[] r = parser.parseLineMulti(nextLine);
            if (r.length > 0) {
                if (result == null) {
                    result = r;
                } else {
                    String[] t = new String[result.length + r.length];
                    System.arraycopy(result, 0, t, 0, result.length);
                    System.arraycopy(r, 0, t, result.length, r.length);
                    result = t;
                }
            }
        } while (parser.isPending());
        return result;
    }

    /**
     * Reads the next line from the file.
     *
     * @return the next line from the file without trailing newline
     * @throws IOException
     *             if bad things happen during the read
     */
    private String getNextLine() throws IOException {
        return contentQueue.poll();
    }

    /**
     * Closes the underlying reader.
     *
     * @throws IOException if the close fails
     */
    public void close() throws IOException {
    }

    /** Watches for content being appended to a CSV file. */
    private static class CsvContentListener extends TailerListenerAdapter {
        final Queue<String> contentQueue;

        CsvContentListener(Queue<String> contentQueue) {
            this.contentQueue = contentQueue;
        }

        @Override
        public void handle(String line) {
            this.contentQueue.add(line);
        }
    }
}

// End CsvStreamReader.java