How to read a CSV file in Java? (Code Tutorial)
Use the OpenCSV library to safely parse CSV files, which automatically handles edge cases such as quoted fields, embedded commas, and newlines; it is recommended to read line by line to save memory, and supports mapping as objects through CsvToBean to avoid manual split or raw stream parsing.
To read a CSV file in Java, you need to handle text parsing, line separation, and field delimitation—especially when fields contain commas, quotes, or newlines. While Java doesn't include a built-in CSV parser, using a reliable library like OpenCSV is the most practical and robust approach.
Use OpenCSV to parse CSV safely
OpenCSV handles edge cases (eg, quoted fields with embedded commas or line breaks) automatically. Add it to your project via Maven:
Then read the file like this:
import com.opencsv.CSVReader;
import java.io.FileReader;
import java.util.List;
try (CSVReader reader = new CSVReader(new FileReader("data.csv"))) {
List<String[]> records = reader.readAll();
for (String[] record : records) {
System.out.println(String.join(", ", record));
}
}Read CSV row-by-row for large files
For memory efficiency—especially with big files—avoid readAll() . Instead, iterate line by line:
try (CSVReader reader = new CSVReader(new FileReader("data.csv"))) {
String[] line;
while ((line = reader.readNext()) != null) {
// Process each row: line[0] is first column, etc.
System.out.println("Name: " line[0] ", Age: " line[1]);
}
}- Each
lineis aString[]where elements correspond to CSV columns - OpenCSV auto-handles quoted fields like
"Smith, Jr.",25→["Smith, Jr.", "25"] - Always use try-with-resources to close the reader and prevent resource leaks
Map rows to objects (optional but helpful)
If your CSV has headers (eg, name,age,email ), use CSVReaderHeaderAware or CsvToBean :
import com.opencsv.bean.CsvToBeanBuilder;
List<Person> people = new CsvToBeanBuilder<Person>(new FileReader("people.csv"))
.withType(Person.class)
.withIgnoreEmptyLine(true)
.build()
.parse();
Your Person class needs matching fields and setters (or public fields), and OpenCSV maps by header name.
Handle common pitfalls
Don't try to split lines manually with String.split(",") —it fails on quoted commas or multiline fields. Also avoid Scanner or raw BufferedReader unless you're writing a custom parser (not recommended for production).
- Always specify character encoding (eg,
new FileReader(file, StandardCharsets.UTF_8)) - Check for
nullor empty rows before accessing array indices - Wrap parsing logic in
try-catchforIOExceptionandCsvException
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