How to read the CSV file with a map with lists with separated elements in Java

Question

I don't know why my previous question is closed so I decide to ask the question in another way. Hi I am a newbie of Java programming , I have some problem about reading data from a CSV file. Here is my CSV file:

1,Ali,1201345673,Normal
2,Siti,1307891435,Normal

Here is how I read the data:

Map<String, List<Customer>> customers =
    Files.lines(Paths.get("customer.csv"))
            .map(line -> line.split("\\s*,\\s*"))
            .map(field -> new Customer(
                    Integer.parseInt(field[0]), field[1],
                    Integer.parseInt(field[2]), field[3]))
            .collect(Collectors
                   .groupingBy(Customer::getName));
    System.out.println (customers);
    return customers;

Customer class:

public class Customer {
private int customerNo;
private String name;
private int phoneNo;
private String status;
public Customer () {}
public Customer (int customerNo, String name, int phoneNo, String status){
    this.customerNo = customerNo;
    this.name = name;
    this.phoneNo = phoneNo;
    this.status = status;
}
public String getName(){
    return name;
}

public String toString(){
    return customerNo + " " + name + " " + phoneNo + " " + status;
}

Then I realize that this is how my map look like:

(Ali = ["1 Ali 1201345673 Normal"] , Siti = ["2 Siti 1307891435 Normal"])

But not the way I want like this:

(Ali = [1 , "Ali" , 1201345673 , "Normal" ] , Siti = [2 , "Siti" , 1307891435 , "Normal" ])

In this for Ali , 1 is an element , Ali is an element , 1201345673 is an element and Normal is another element.

The data of every person has been read into an element in my List so I can't not output them like an Array list . So the problem is how can I separate the every element in the list when I read the CSV data and I really need the Map function of the program so please keep it , or maybe how can I read the data as a array list in my map. Thank you for your attention.

Answer 1

I believe the following achieves what you desire.

/*
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
 */
Supplier<List<List<Object>>> s = () -> new ArrayList<List<Object>>();

BiConsumer<List<List<Object>>, Customer> b = (l, c) -> {
            l.add(c.toList());
};

BinaryOperator<List<List<Object>>> o = (l1, l2) -> {l1.addAll(l2); return l1;};

Collector<Customer, List<List<Object>>, List<List<Object>>> c = Collector.of(s, b, o);

Map<String, List<List<Object>>> customers =
        Files.lines(Paths.get("customer.csv"))
             .map(line -> line.split("\\s*,\\s*"))
             .map(field -> new Customer(Integer.parseInt(field[0]),
                                        field[1],
                                        Integer.parseInt(field[2]),
                                        field[3]))
             .collect(Collectors.groupingBy(Customer::getName,
                                            Collectors.mapping(Function.identity(), c)));
System.out.println(customers);

The output is

{Siti=[[2, Siti, 1307891435, Normal]], Ali=[[1, Ali, 1201345673, Normal]]}

I created a custom Collector, i.e. I wrote an implementation of the Collector interface.

Each value in the Map, i.e. customers, is a list of lists. According to your sample CSV file, there are two lines in the file, each with a separate name. Hence the Map contains two entries and the value for each entry is a list that contains a single element which is itself a list. That's why the output shows double [ and ] characters.

Note that I added method toList to class Customer

public class Customer {
    private int customerNo;
    private String name;
    private int phoneNo;
    private String status;

    public Customer() {
    }

    public Customer(int customerNo, String name, int phoneNo, String status) {
        this.customerNo = customerNo;
        this.name = name;
        this.phoneNo = phoneNo;
        this.status = status;
    }

    public String getName() {
        return name;
    }

    public List<Object> toList() {
        return List.of(customerNo, name, phoneNo, status);
    }

    public String toString() {
        return customerNo + " " + name + " " + phoneNo + " " + status;
    }
}

Answer 2

That's because of toString() method. It defines how the class will be printed by basically defining a custom formatted string.

if you change it to as following :

public String toString(){
    return customerNo + ", " + name + ", " + phoneNo + ", " + status;
}

It will print as :

Ali = ["1, Ali, 1201345673, Normal"]

You can customize this function to print it the way you want.

try this :

public String toString(){
    return customerNo + ", \"" + name + "\", " + phoneNo + ", \"" + status + "\"";
}