Java - 如何将 CSV 文件读入 Map <string, map<string, string> ></string,>

Question

Input (CSV File)

Header1,Header2,Header3

Data1,Data2,Data3

Data4,Data5,Data6

Data7,,

,,Data8

I am trying to parse through a CSV file similar to the above structure and store the data into a Map<String (Row Number), Map<String (Column Header), String (Column Value)>>.

Answer 1

Assuming your file is well formed and each row has the same column count as your header, something like below migght be a starting point:

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public final class Example {

    public static void main(String[] args) throws IOException {

        //create a map    
        Map<String, Map<String, String>> map = new LinkedHashMap<>();

        Path filePath = Paths.get("path to your/test.csv");
        Charset charset = StandardCharsets.UTF_8;

        //read the file
        List<String> fileContent = Files.readAllLines(filePath, charset);

        // get the header
        String[] header = fileContent.get(0).split(",");

        AtomicInteger lineNumber = new AtomicInteger(1);

        //fill the map
        fileContent.stream()
                   .skip(1)
                   .forEach(line -> map.put(
                           String.valueOf(lineNumber.getAndIncrement()),
                           getRowData(header, line.split(","))));

        System.out.println(map);
    }

    // helper method to make the filling of the map in the stream readable
    private static Map<String, String> getRowData(final String[] header, final String[] line) {
        return IntStream.range(0, header.length)
                        .mapToObj(i -> Map.entry(header[i], line[i]))
                        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
    }
}