compare 2 csv files in java code example

Example 1: java comparing-two-csv-files-in-java

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

/* file1 - file2 = file3*/
public class CompareCSV {
public static void main(String args[]) throws FileNotFoundException, IOException
{
    String path="D:\\csv\\";
    String file1="file1.csv";
    String file2="file2.csv";
    String file3="p3lang.csv";
    ArrayList al1=new ArrayList();
    ArrayList al2=new ArrayList();
    //ArrayList al3=new ArrayList();

    BufferedReader CSVFile1 = new BufferedReader(new FileReader(path+file1));
    String dataRow1 = CSVFile1.readLine();
    while (dataRow1 != null)
    {
        String[] dataArray1 = dataRow1.split(",");
        for (String item1:dataArray1)
        { 
           al1.add(item1);
        }

        dataRow1 = CSVFile1.readLine(); // Read next line of data.
    }

     CSVFile1.close();

    BufferedReader CSVFile2 = new BufferedReader(new FileReader(path+file2));
    String dataRow2 = CSVFile2.readLine();
    while (dataRow2 != null)
    {
        String[] dataArray2 = dataRow2.split(",");
        for (String item2:dataArray2)
        { 
           al2.add(item2);

        }
        dataRow2 = CSVFile2.readLine(); // Read next line of data.
    }
     CSVFile2.close();

     for(String bs:al2)
     {
         al1.remove(bs);
     }

     int size=al1.size();
     System.out.println(size);

     try
        {
            FileWriter writer=new FileWriter(path+file3);
            while(size!=0)
            {
                size--;
                writer.append(""+al1.get(size));
                writer.append('\n');
            }
            writer.flush();
            writer.close();
        }
        catch(IOException e)
        {
            e.printStackTrace();
        }
}}

Example 2: java code to compare csv file against a table

HashMap<String, String> f1 = new HashMap<String, String>();
HashMap<String, String> f2 = new HashMap<String, String>();
// read f1, f2; use PK field as the key
List<String> deleted = new ArrayList<String>();
List<String> updated = new ArrayList<String>();
for(Map.Entry<String, String> entry : f1.keySet()) {
    if(!f2.containsKey(entry.getKey()) {
        deleted.add(entry.getValue());
    } else {
        if(!f2.get(entry.getKey().equals(f1.getValue())) {
            updated.add(f1.getValue());
        }
    }
}
for(String key : f1.keySet()) {
    f2.remove(key);
}
// f2 now contains only "new" rows