Question

* readCsvFile() -- Read in a CSV File and return a list of entries in that file.
   * @param filePath -- Path to file being read in.
   * @param classType -- Class of entries being read in.
   * @return -- List of entries being returned.
   */
   public <T> List<T> readCsvFile(String filePath, Class<T> classType){
       return null;
   }

implement this class. Return a list of T type. dont worry about CSV format. Just assume there is a constructor for the class type and it has 3 elements. make something up

Answer 1

Below is the complete program to run and test the method (readCsvFile) using Employee class. You can use any other class as per your requirement which has a public constructor with three arguments. I have mentioned inline comments as well.

Note: Don't forget to change the classes specified in parameterTypes variable according to the data type of variables in your class. Order of parameters should be same in parameterTypes variable as specified in the constructor.

Employee.java

public class Employee {

    Integer id;
    String fname, lname;

    public Employee(Integer id, String fname, String lname) {
        this.id = id;
        this.fname = fname;
        this.lname = lname;
    }

    @Override
    public String toString() {
        return "Employee{" + "id = " + id + ", fname = " + fname +
                ", lname = " + lname + "}";
    }
}

Test.java to run and test the code

import java.io.*;
import java.util.*;

public class Test {
    public static void main(String[] args) throws Exception {
        Test test = new Test();
        List<Employee> empList =  test.readCsvFile("src/test.csv", Employee.class);
        empList.stream().forEach(System.out::println);
    }

    public <T> List<T> readCsvFile(String filePath, Class<T> classType) throws Exception {
        List<T> result = new ArrayList<>();
        //open input stream to read from the file
        BufferedReader reader = new BufferedReader(new FileReader(new File(filePath)));
        String line;
        while ((line = reader.readLine()) != null) {
            //split the line from comma. CSV file has comma(',') as default value separator
            String[] splitString = line.split(",");
            //declare parameter types accepted by the constructor
            //update it as per your class, i have considered the constructor which takes 2 String and 1 Integer parameters
            Class[] parameterTypes = new Class[]{Integer.class, String.class, String.class};
            //set the values from splitString array which is read from csv file
            Object[] values = new Object[3];
            values[0] = Integer.parseInt(splitString[0].trim());
            values[1] = splitString[1].trim();
            values[2] = splitString[2].trim();
            T t = classType.getConstructor(parameterTypes).newInstance(values);
            result.add(t);
        }
        //close the connection with input stream
        reader.close();
        return result;
    }
}

Test.csv File:

Screenshot of code:

Output: