How to read a CSV file and store the information in a class, when I don't know the order of the columns that will be in the CSV file?

Question

I have an assignment, where I need to read a CSV file. I know that the first line of the CSV file will have the following information:

LabelA,LabelB,LabelC,LabelD

and that all of the lines below will have the corresponding information, so all the following lines of the CSV file looks like this:

InfoA,InfoB,InfoC,InfoD

I have created a class that stores all of that information, and then I need to create a HashMap to store all of those objects, each object with the information of a different line, however, the CSV File that I will be reading has a randomized order of the columns, so I might receive a CSV File that has the first line as:

LabelD,LabelA,LabelB,LabelC

Which would make the following lines as:

InfoD,InfoA,InfoB,InfoC

How can I approach this? Regardless of the order of the columns of the CSV file, I need to correctly store that information in an object.

Before this assignment, the order of the columns was always the same, so I was storing each line on a string, then splitting the string, and then putting the information in that order in the constructor of the object, but I can no longer do this, since the order will be randomized.

I am not allowed to use any dependency other than java.io.File, java.util.Scanner, and java.util.HashMap.

Answer 1

If you want to use core java only you can try this:

public class Main {
    public static void main(String[] args) {
        StringReader reader = new StringReader(
                """
                        Col1,Col2
                        aa,bb
                        cc,dd
                        """);

        Scanner scanner = new Scanner(reader);

        String[] header = scanner.nextLine().split(",");
        Map<String, Integer> mapping = new HashMap<>();
        for (int i = 0; i < header.length; i++) {
            mapping.put(header[i].trim(), i);
        }

        List<MyBean> list = new ArrayList<>();
        while (scanner.hasNext()) {
            String[] data = scanner.nextLine().split(",");
            MyBean value = new MyBean();
            value.setColum1(data[mapping.get("Col1")]);
            value.setColum2(data[mapping.get("Col2")]);
            list.add(value);
        }

        System.out.println(list);
    }

    @Data
    public static class MyBean {
        private String colum1;
        private String colum2;
    }
}

Answer 2

Here is a little example:

public class Main {
    public static void main(String[] args) {
        CSVReader csvReader = new CSVReader(new StringReader(
                """
                        Col1, Col2
                        aa, bb
                        cc, dd
                        """));
        CsvToBean<MyBean> parser = new CsvToBeanBuilder<MyBean>(csvReader)
                .withType(MyBean.class).build();
        List<MyBean> beans = parser.parse();

        System.out.println(beans);
    }
    
    @Data
    public static class MyBean {
        @CsvBindByName(column = "Col1")
        private String colum1;
        @CsvBindByName(column = "Col2")
        private String colum2;
    }
}

Here is required dependencies:

        <dependency>
            <groupId>com.opencsv</groupId>
            <artifactId>opencsv</artifactId>
            <version>5.5</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.24</version>
            <scope>provided</scope>
        </dependency>

Lombock is optional. You can create your bean the way you want.