如何使用Java将基于列名而不是按列索引的特定列从一个CSV文件转换为另一个CSV

Question

I am writing one Java utility where I want to transfer specific column based on Column Name from one CSV to another CSV file instead of ArrayIndex .

Below is the program which is working absolutely fine when I am selecting specific columns based on array Index but I want to filter my columns based on Column Name only.

package be.ing.data;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.concurrent.TimeUnit;

public class ImportExportCSV{

    public static void main(String[] args){
        // Set your splitter, mostly "," or ";"
         String csvFile = "C:/Data/input_file.csv";
         String exportCSVFile = "C:/Data/output_file.csv";
    //  String csvSplitter = "\t";
        String csvSplitter = ",";
        String line = "";
        BufferedReader br = null;
        PrintWriter output = null;
        Date date = new Date();
        try {
        // A buffered reader on the input file
         br = new BufferedReader(new FileReader(csvFile));
        // A writer to the output file
         output = new PrintWriter(exportCSVFile, "UTF-8");
        // Read line after line until EOF
            int count = 0;
            long startTime = System.nanoTime();
            System.out.println("Start Execution Time : "+startTime);

            while ((line = br.readLine()) != null) {
            String[] cols = line.split(csvSplitter);
            output.println(cols[0] + csvSplitter +
                    cols[20]);              
            count++;
            }
            System.out.println("Total Record count :"+count);
            long endTime = System.nanoTime();
            System.out.println("Completion Time : "+ (endTime-startTime));
            System.out.println("Time in seconds"+ TimeUnit.SECONDS.convert(endTime, TimeUnit.NANOSECONDS));
        }catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                    output.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }   
    }
}

Answer 1

You have to convert String[] cols to a List<String> in order to get the index of a column based on his name and then use that index to access the value for every lines of your csv file :

For example if you want to print for every lines of your csv file the value of the column "myColumnName" :

String[] cols = line.split(csvSplitter);
List<String> columns = Arrays.asList(cols);
System.out.println(cols[columns.indexOf("myColumnName")]);