This is done via the java.io.BufferedWriter
try { bufferedWriter = new java.io.BufferedWriter(new java.io.FileWriter('C:\\Temp\\testFile.txt', true)); bufferedWriter.write('This is my new line of data'); bufferedWriter.newLine(); bufferedWriter.flush(); } finally { if (bufferedWriter !== null) { try { bufferedWriter.close(); } catch (err) { // we will just ignore this error } } }