Skip non-CSV head

Some CSV files contain one or more lines of text before the actual CSV data starts. For example, it could look like this:

example.csv

This is an example of a CSV file that contains
three lines before the actual CSV records.

header 1,header 2
value 1,value 2

Strictly speaking, such a file is not a valid CSV file as defined by the CSV specification (RFC 4180).

The main problem with those files is:

• An exception would be thrown unless the options ignoreDifferentFieldCount() and skipEmptyLines() are set.
• When working with named fields, the very first line (This is an example of a CSV file that contains) would be interpreted as the actual header line.

FastCSV comes with two features to handle such files:

• skipLines(int lineCount): Skip a specific number of lines (lineCount) regardless of their content.
• skipLines(Predicate<String> predicate, int maxLines): Skip lines until a specific line (e.g., the header) is found. Stop skipping after a specific number of lines (maxLines).

Note

Do not mix this with comments in CSV files. Comments are lines that start with a specific character (e.g., #) and can be skipped by FastCSV using a CommentStrategy. See the example on how to handle comments for more information.

Example

This example demonstrates how to skip non-CSV head lines when reading such a CSV file with FastCSV.

ExampleCsvReaderWithNonCsvAtStart.java

package example;

import java.io.IOException;
import java.util.function.Predicate;

import de.siegmar.fastcsv.reader.CsvReader;

/**
 * Example for reading CSV data with non-CSV data before the actual CSV header.
 */
public class ExampleCsvReaderWithNonCsvAtStart {

    private static final String DATA = """
        Your CSV file contains some non-CSV data before the actual CSV header?
        And you don't want to (mis)interpret them as CSV header? No problem!

        header1,header2
        foo,bar
        """;

    public static void main(final String[] args) throws IOException {
        alternative1();
        alternative2();
    }

    private static void alternative1() throws IOException {
        System.out.println("Alternative 1 - ignore specific number of lines");

        try (var csv = CsvReader.builder().ofNamedCsvRecord(DATA)) {
            // Skip the first 3 lines
            System.out.println("Skipping the first 3 lines");
            csv.skipLines(3);

            // Read the CSV data
            csv.forEach(System.out::println);
        }
    }

    private static void alternative2() throws IOException {
        System.out.println("Alternative 2 - wait for a specific line");

        final Predicate<String> isHeader = line ->
            line.contains("header1");

        try (var csv = CsvReader.builder().ofNamedCsvRecord(DATA)) {
            // Skip until the header line is found, but not more than 10 lines
            final int actualSkipped = csv.skipLines(isHeader, 10);
            System.out.println("Found header line after skipping " + actualSkipped + " lines");

            // Read the CSV data
            csv.forEach(System.out::println);
        }
    }

}

You also find this source code example in the FastCSV GitHub repository.