[スニペット] Java8 CSVヘッダーをマップで置換

import com.opencsv.CSVReader;
import com.opencsv.CSVWriter;

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.*;

public class CSVHeaderReplace {
    public static void main(String[] args) throws IOException {
        String inputFile = "input.csv";
        String outputFile = "output.csv";

        // 英語→和名のマッピング
        Map<String, String> headerMap = new HashMap<>();
        headerMap.put("Name", "名前");
        headerMap.put("Math", "数学");
        headerMap.put("Science", "理科");
        headerMap.put("English", "英語");

        try (
            CSVReader reader = new CSVReader(new FileReader(inputFile));
            CSVWriter writer = new CSVWriter(new FileWriter(outputFile))
        ) {
            List<String[]> allRows = reader.readAll();
            if (allRows.isEmpty()) return;

            // 最初の行 = ヘッダー
            String[] originalHeader = allRows.get(0);
            String[] replacedHeader = Arrays.stream(originalHeader)
                    .map(col -> headerMap.getOrDefault(col, col)) // 対応がない場合はそのまま
                    .toArray(String[]::new);

            writer.writeNext(replacedHeader);

            // 2行目以降はデータ行としてそのまま書き出し
            for (int i = 1; i < allRows.size(); i++) {
                writer.writeNext(allRows.get(i));
            }
        }
    }
}

import com.opencsv.CSVReader;

import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class HeaderMappingLoader {

    public static Map<String, String> loadHeaderMap(String mappingFilePath) throws IOException {
        Map<String, String> map = new HashMap<>();

        try (CSVReader reader = new CSVReader(new FileReader(mappingFilePath))) {
            String[] line;
            while ((line = reader.readNext()) != null) {
                if (line.length >= 2) {
                    String key = line[0].trim();
                    String value = line[1].trim();
                    map.put(key, value);
                }
            }
        }

        return map;
    }
}

CSVWriter writer = new CSVWriter(
    new OutputStreamWriter(new FileOutputStream(outputFile), StandardCharsets.UTF_8),
    CSVWriter.DEFAULT_SEPARATOR,
    CSVWriter.NO_QUOTE_CHARACTER,
    CSVWriter.DEFAULT_ESCAPE_CHARACTER,
    System.lineSeparator()
);