File I/O - loading data and creating txt file from CSV file.

 

students.csv 

id,name
1,A
2,B
3,C

 

 


public class StudentInfo {
    private int id;
    private String name;
    public StudentInfo(int id, String name){
        this.id = id;
        this.name = name;
    }
    public int studentId(){
        return id;
    }
    @Override
    public String toString(){
        return "Student Id: " + this.id + ", " + "name: " + this.name + "\n";
    }
}
 

public class Main {
 
    public static void main(String[] args) throws FileNotFoundException {
        //ArrayList
        ArrayList<StudentInfo> studentInfos = new ArrayList<>();
 
        try {
            //read the CSV file
            BufferedReader sc = new BufferedReader(new FileReader("src" + File.separator + "csv_input" + File.separator + "students.csv"));
 
            //skip the first line
            String re = sc.readLine(); //id, name
 
            //while loop until the end of file
            while ((re = sc.readLine()) != null) {
            //while (re != null) { // If only 're' assigned, NumberFormatException error will occur because 're' has 'id','name' as String
                //split comma-separated
                String[] data = re.split(",");
                //way1. create method 
 //assign to ArrayList 
                //StudentInfo student = createFile(data);
                //studentInfos.add(student);
 
                //way2. creating object inside the add method.  
                studentInfos.add(new StudentInfo(Integer.parseInt(data[0]), data[1]));
 
                //re = sc.readLine(); // If the data is String, assigning 're' and put this line to read next line is fine. 
                //But, It occurs Error here. Because, this example have to convert String to Int to calculate. 
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
 
        //create text file
        File file = new File("src" + File.separator + "txt_output" + File.separator + "reportCard.txt");
        
        BufferedWriter output = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file.getPath()), StandardCharsets.UTF_8));
 
        try {
            for (int i = 0; i < studentInfos.size(); i++) {
                output.write(studentInfos.get(i).toString());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            output.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
//    way1. declare createFile method to assign data
//    private static StudentInfo createFile(String[] s) {
//        int id = Integer.parseInt(s[0]);
//        String name = s[1];
//        return new StudentInfo(id, name);
//    }
}
 
 
 
 

 

 

reportCard.txt

Student Id: 1, name: A
Student Id: 2, name: B
Student Id: 3, name: C