How can we write data in CSV from Beanshell - jmeter

Question

While executing below code in eclipse its working but not working in bean shell ? it displaying error near writer.write(data);
So please help me out how can we pass string array from beanshell to csv
import java.io.*;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.util.List;
int i;
File file = new File("/home/sarvesh/Desktop/sgi/10");
int filecount = file.list().length;
File[] files = file.listFiles();
String[] imageString = new String[filecount];
for ( i =0;i<filecount;i++) {
File f = new File(files[i].getAbsolutePath());
FileInputStream fis = new FileInputStream(f);
byte [] byteArray = new byte[(int) f.length()];
fis.read(byteArray);
imageString[i] = Base64.getEncoder().encodeToString(byteArray);
//vars.put("imagData",imageString[i]);
FileWriter writer = new FileWriter("/home/sarvesh/Desktop/sgi/base64_csv.csv");
// List<String> data = new ArrayList<String>();
ArrayList data = new ArrayList();
data.add(new String[] {imageString[i] });
**writer.write(data);**
// writer.write(imageString[i]);
// writer.close();
System.out.println("***********************************************");
System.out.println("Base 64 conversion of Image : " + i + " ::" + imageString[i]);
System.out.println("File Path : " + f.getAbsolutePath());
System.out.println("***********************************************");
}

Answer 1

Beanshell is not Java, it doesn't support diamond operators therefore you need to change this line:
List<String> data = new ArrayList<String>();
to this one:
List data = new ArrayList();
Starting from JMeter 3.1 you should rather be using JSR223 Test Elements and Groovy language for scripting
Your approach will work given you run your test with 1 thread (virtual user), if there will be more users - you'll run into the race condition resulting into file corruption/data loss so if you need to write some specific data into some specific file it's better to go for the Flexible File Writer. Alternatively you can use Critical Section Controller but it will slow down your test