JavaでCSVを読み込む方法を解説！標準機能からおすすめライブラリまで実装例を比較

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class StandardCsvReader {
    public static void main(String[] args) {
        String filePath = "data.csv";
        // try-with-resourcesを使用して自動的にクローズする
        try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
            String line;
            while ((line = br.readLine()) != null) {
                // カンマで分割。第2引数に-1を指定すると末尾の空要素も保持される
                String[] values = line.split(",", -1);
                
                // データの処理（ここでは出力のみ）
                for (String value : values) {
                    System.out.print(value + " | ");
                }
                System.out.println();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.nio.file.Files;
import java.nio.file.Paths;
import java.io.IOException;
import java.util.stream.Stream;

public class ModernStandardReader {
    public static void main(String[] args) {
        String filePath = "data.csv";

        try (Stream<String> lines = Files.lines(Paths.get(filePath))) {
            lines.map(line -> line.split(",", -1))
                 .forEach(values -> {
                     System.out.println("処理中: " + values[0]);
                 });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-csv</artifactId>
    <version>1.10.0</version>
</dependency>

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

import java.io.FileReader;
import java.io.Reader;
import java.io.IOException;

public class ApacheCommonsCsvExample {
    public static void main(String[] args) {
        String filePath = "data.csv";
        
        try (Reader in = new FileReader(filePath)) {
            // ヘッダーを自動取得する設定でパース
            CSVFormat format = CSVFormat.DEFAULT.builder()
                    .setHeader()
                    .setSkipHeaderRecord(true)
                    .build();

            CSVParser parser = format.parse(in);

            for (CSVRecord record : parser) {
                // 列名（ヘッダー名）で値を取得できる
                String id = record.get("ID");
                String name = record.get("名前");
                String email = record.get("メールアドレス");

                System.out.println(id + ": " + name + " (" + email + ")");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

<dependency>
    <groupId>com.opencsv</groupId>
    <artifactId>opencsv</artifactId>
    <version>5.9</version>
</dependency>

import com.opencsv.bean.CsvBindByName;

public class UserBean {
    @CsvBindByName(column = "ID")
    private int id;

    @CsvBindByName(column = "名前")
    private String name;

    @CsvBindByName(column = "メールアドレス")
    private String email;

    // Getter, Setterは省略
}

import com.opencsv.bean.CsvToBeanBuilder;
import java.io.FileReader;
import java.util.List;

public class OpenCsvExample {
    public static void main(String[] args) {
        String filePath = "data.csv";

        try (FileReader reader = new FileReader(filePath)) {
            List<UserBean> users = new CsvToBeanBuilder<UserBean>(reader)
                    .withType(UserBean.class)
                    .build()
                    .parse();

            for (UserBean user : users) {
                System.out.println(user.getName() + "さんをオブジェクトとして処理中");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-csv</artifactId>
    <version>2.15.2</version>
</dependency>

import com.fasterxml.jackson.databind.MappingIterator;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;
import com.fasterxml.jackson.dataformat.csv.CsvSchema;

import java.io.File;
import java.util.Map;

public class JacksonCsvExample {
    public static void main(String[] args) {
        try {
            CsvMapper mapper = new CsvMapper();
            // ヘッダーありのスキーマを設定
            CsvSchema schema = CsvSchema.emptySchema().withHeader();

            File csvFile = new File("data.csv");
            MappingIterator<Map<String, String>> it = mapper
                    .readerFor(Map.class)
                    .with(schema)
                    .readValues(csvFile);

            while (it.hasNext()) {
                Map<String, String> row = it.next();
                System.out.println("名前: " + row.get("名前"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import java.nio.charset.Charset;
// ...中略...
try (FileReader fr = new FileReader("data.csv", Charset.forName("Windows-31J"))) {
    // このReaderを各ライブラリに渡す
}