tl;dr
- Use the Java Collections rather than arrays, specifically a
List or Set, to auto-expand as you add items.
- Define a class to hold your data read from CSV, instantiating an object for each row read.
- Use the Apache Commons CSV library to help with the chore of reading/writing CSV files.
Class to hold data
Define a class to hold the data of each row being read from your CSV. Let's use Person class with a given name and surname, to be more concrete than the example in your Question.
In Java 16 and later, more briefly define the class as a record.
record Person ( String givenName , String surname ) {}
In older Java, define a conventional class.
package work.basil.example;
public class Person {
public String givenName, surname;
public Person ( String givenName , String surname ) {
this.givenName = givenName;
this.surname = surname;
}
@Override
public String toString ( ) {
return "Person{ " +
"givenName='" + givenName + '\'' +
" | surname='" + surname + '\'' +
" }";
}
}
Collections, not arrays
Using the Java Collections is generally better than using mere arrays. The collections are more flexible and more powerful. See Oracle Tutorial.
Here we will use the List interface to collect each Person object instantiated from data read in from the CSV file. We use the concrete ArrayList implementation of List which uses arrays in the background. The important part here, related to your Question, is that you can add objects to a List without worrying about resizing. The List implementation is responsible for any needed resizing.
If you happen to know the approximate size of your list to be populated, you can supply an optional initial capacity as a hint when creating the List.
Apache Commons CSV
The Apache Commons CSV library does a nice job of reading and writing several variants of CSV and Tab-delimited formats.
Example app
Here is an example app, in a single PersoIo.java file. The Io is short for input-output.
Example data.
GivenName,Surname
Alice,Albert
Bob,Babin
Charlie,Comtois
Darlene,Deschamps
Source code.
package work.basil.example;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVRecord;
import java.io.BufferedReader;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
public class PersonIo {
public static void main ( String[] args ) {
PersonIo app = new PersonIo();
app.doIt();
}
private void doIt ( ) {
Path path = Paths.get( "/Users/basilbourque/people.csv" );
List < Person > people = this.read( path );
System.out.println( "People: \n" + people );
}
private List < Person > read ( final Path path ) {
Objects.requireNonNull( path );
if ( Files.notExists( path ) ) {
System.out.println( "ERROR - no file found for path: " + path + ". Message # de1f0be7-901f-4b57-85ae-3eecac66c8f6." );
}
List < Person > people = List.of(); // Default to empty list.
try {
// Hold data read from file.
int initialCapacity = ( int ) Files.lines( path ).count();
people = new ArrayList <>( initialCapacity );
// Read CSV file.
BufferedReader reader = Files.newBufferedReader( path );
Iterable < CSVRecord > records = CSVFormat.RFC4180.withFirstRecordAsHeader().parse( reader );
for ( CSVRecord record : records ) {
// GivenName,Surname
// Alice,Albert
// Bob,Babin
// Charlie,Comtois
// Darlene,Deschamps
String givenName = record.get( "GivenName" );
String surname = record.get( "Surname" );
// Use read data to instantiate.
Person p = new Person( givenName , surname );
// Collect
people.add( p ); // For real work, you would define a class to hold these values.
}
} catch ( IOException e ) {
e.printStackTrace();
}
return people;
}
}
When run.
People:
[Person{ givenName='Alice' | surname='Albert' }, Person{ givenName='Bob' | surname='Babin' }, Person{ givenName='Charlie' | surname='Comtois' }, Person{ givenName='Darlene' | surname='Deschamps' }]
Listinstead of a fixed-size array so it can grow on demand. Convert to an array later if you really must.String.split(",")will split a line into an array. Collect each line in aList<String[]>.