Compare two CSV files on multiple column and create new CSV file in Java-CodePudding

I have two csv files File 1:

ID,NAME
1,FOO
2,BAR
3,XYZ

File 2:

ID,NAME,DOB
3,XYZ,02/03/1999
4,BAR,01/01/1995
1,FOO,01/01/1996

How can I select rows from CSV File 2 which has columns ID,NAME value matched in File 1 in java language.

Expected Result:

ID,NAME,DOB
3,XYZ,02/03/1999
1,FOO,01/01/1996

CodePudding user response：

Basically you want to perform Vlookup operation .

You can get desired outcome by using Apache POI library. This library provides set of methods to perform Vlookup.

You can refer to the below resources for detailed understanding. https://poi.apache.org/apidocs/dev/org/apache/poi/ss/formula/functions/Vlookup.html

CodePudding user response：

There are a lot of API's that support functions like comparing .csv files. However, Java also has its own ways to do this.

I'll explain it step by step:

First, you should read the two files into the program. java.io provides some classes with this functionality.
Then, after the content of both files is stored in an appropriate data structure, you can compare them.
You can then simply store the matching lines in another data structure and return them.
Last but not least, you also have to write to a new or already existing file using classes from java.io.

Here is a method to read in files:

  public ArrayList<String> readInFile(String absoluteFilePath) {

        BufferedReader reader = null;
        ArrayList<String> csvContent = new ArrayList<>();
        String currentLine;
        
        try {
            reader = new BufferedReader(new FileReader(absoluteFilePath));
            
            while((currentLine = reader.readLine()) != null) {
                csvContent.add(currentLine);
            }
            reader.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
        return csvContent;
    }

The method uses a BufferedReader to read the file and adds it line by line to the ArrayList

Writing to a .csv file is just as easy as reading from one. You just have to decide whether you want to write to an existing file or to a file that already exists.

Here is a method to write into files:

  public void writeToFile(ArrayList<String> csvContent, String absoluteFilePath) {

        BufferedWriter writer = null;

        try {
            writer = new BufferedWriter(new FileWriter(absoluteFilePath));

            for (int i = 0; i < csvContent.size(); i  ) {
                writer.write(csvContent.get(i)   "\n");
            }

            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

This method uses a BufferedWriter to either create a file at the given path or overwrite an existing one and writes the contents of the ArrayList into the file.

Good luck!