In Java, using StringBuilder, we can build a csv file content and write to a csv file. In this example, we create a csv file with the content below. 

TestID,TestModule,TestType
1,Login,Regression
2,Logout,Regression
3,Change User Settings,Regression

write the following code in the "WriteCsvFileStringBuilder.java" class

package com.example.csv;
import com.example.file.WriteToFile;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class WriteCsvFileStringBuilder {

    public static StringBuilder csvRecords = new StringBuilder();

    public static void main(String[] args) {

        String header = WriteCsvHeader(new String[]{"TestID", "TestModule", "TestType"});
        WriteCsvRecords(new String[]{"1", "Login", "Regression"});
        WriteCsvRecords(new String[]{"2", "Logout", "Regression"});
        WriteCsvRecords(new String[]{"3", "Change User Settings", "Regression"});



        try {
            WriteToFile.WriteToFile(header + csvRecords.toString(), "CsvStringBuilder.csv");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void WriteToFile(String fileContent, String fileName) throws IOException {
        String projectPath = System.getProperty("user.dir");
        String tempFile = projectPath + File.separator + fileName;
        File file = new File(tempFile);
        // if file does exists, then delete and create a new file
        if (file.exists()) {
            try {
                File newFileName = new File(projectPath + File.separator + "backup_" + fileName);
                file.renameTo(newFileName);
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        FileWriter fw = new FileWriter(file.getAbsoluteFile());
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(fileContent);
        System.out.println(fileContent);
        bw.close();

    }

    public static String WriteCsvHeader(String[] headers) {
        StringBuilder csvHeader = new StringBuilder();
        int totalHeaders = headers.length;
        for (int i = 0; i < totalHeaders; i++) {
            //if not last header, append comma after each header
            if (i != totalHeaders - 1) {
                csvHeader.append(headers[i]);
                csvHeader.append(",");
            }
            //if last header, just append the column
            else {
                csvHeader.append(headers[i]);
            }
        }
        csvHeader.append("\n");
        return csvHeader.toString();
    }

    public static void WriteCsvRecords(String[] records) {
        int numberOfColumnsInRecords = records.length;
        for (int i = 0; i < numberOfColumnsInRecords; i++) {
           //if not the last column, append comma after each column
            if (i != numberOfColumnsInRecords - 1) {
                csvRecords.append(records[i]);
                csvRecords.append(",");
            }
            //if last column, just append the column
            else {
                csvRecords.append(records[i]);
            }
        }
        csvRecords.append("\n");
    }
}

Run the above code and open the created csv file "". You will see the following content .

TestID,TestModule,TestType
1,Login,Regression
2,Logout,Regression
3,Change User Settings,Regression