Convert CSV values to a HashMap key value pairs in JAVA

Question

HI I have a csv called test.csv . I am trying to read the csv line by line and convert the values into a hash key value pairs . Here is the code :-

Answer 1

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;
public class Example {


    public static void main(String[] args) {

        String csvFile = "test.csv";
        String line = "";
        String cvsSplitBy = ",";
        HashMap<String, String> list = new HashMap<>();
        try (BufferedReader br = new BufferedReader(new FileReader(csvFile))) {

            while ((line = br.readLine()) != null) {

                // use comma as separator
                String[] country = line.split(cvsSplitBy);

                //System.out.println(country[0] +"  "  + country[1]);
                list.put(country[0], country[1]);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println(list);

    }
   // enter code here

}

Answer 2

String.split is rubbish for parsing CSV. Either use the Guava Splitter or a proper CSV parser. You can parse CSV into beans using the Jackson CSV mapper like this:

public class CSVPerson{
  public String firstname;
  public String lastname;
  //etc
}

CsvMapper mapper = new CsvMapper();
CsvSchema schema = CsvSchema.emptySchema().withHeader().withColumnSeparator(delimiter);
MappingIterator<CSVPerson> it = = mapper.reader(CSVPerson).with(schema).readValues(input);
while (it.hasNext()){
  CSVPerson row = it.next();
}

more info at http://demeranville.com/how-not-to-parse-csv-using-java/

Answer 3

Beside the problem you have with the first number which its not a pair and its causing the Exception, you will not want to use Hashmap, since hashmap use a unique key, so line 2 will replace values from line 1.

You should use a MultiMap, or a List of pairs in this case.

Answer 4

Look at the output of the call String arr[] = str[i].split(":"); arr[1] does not exists for the first element in your CSV file which happens to be 1, 2... You can start the loop with int i=0 to fix this issue.

Answer 5

In your String when you split it on first time only contains arr[0] as 1 nothing in arr[1] so it will cause an Exception

If you does not need the 1,2, etc.. You can look the following code:

        String str[] = line.split(",");
        for(int i=1;i<str.length;i++){
            String arr[] = str[i].split(":");
            map.put(arr[0], arr[1]);
        }

Answer 6

using openCSV would be one way to do it

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import au.com.bytecode.opencsv.CSVReader;

public class CsvFileReader {
    public static void main(String[] args) {

        try {
            System.out.println("\n**** readLineByLineExample ****");
            String csvFilename = "C:/Users/hussain.a/Desktop/sample.csv";
            CSVReader csvReader = new CSVReader(new FileReader(csvFilename));
            String[] col = null;
            while ((col = csvReader.readNext()) != null) 
            {
                System.out.println(col[0] );
                //System.out.println(col[0]);
            }
            csvReader.close();
        }
        catch(ArrayIndexOutOfBoundsException ae)
        {
            System.out.println(ae+" : error here");
        }catch (FileNotFoundException e) 
        {
            System.out.println("asd");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("");
            e.printStackTrace();
        }
    }
}

the jar is available here