从文件中读取预订机票，并将预订的航班写入文件。使用BufferedReader读取文件，该文件每行总是有10个元素，用逗号分隔。接下来，使用BufferedWriter在进行保留后写入文件。

以下是Java代码示例：

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FlightBooking {
    public static void main(String[] args) {
        String inputFilePath = "input.txt";
        String outputFilePath = "output.txt";
        try {
            BufferedReader reader = new BufferedReader(new FileReader(inputFilePath));
            BufferedWriter writer = new BufferedWriter(new FileWriter(outputFilePath));
            String line;
            while ((line = reader.readLine()) != null) {
                String[] booking = line.split(",");
                String flightNumber = booking[0];
                String departure = booking[1];
                String destination = booking[2];
                String date = booking[3];
                String time = booking[4];
                String firstName = booking[5];
                String lastName = booking[6];
                String email = booking[7];
                String phone = booking[8];
                String seat = booking[9];
                // Do something with the booking information, e.g. write to a database
                // Write the booking to the output file
                writer.write(flightNumber + "," + departure + "," + destination + "," + date + "," + time + "," + firstName + "," + lastName + "," + email + "," + phone + "," + seat);
                writer.newLine();
            }
            reader.close();
            writer.close();
            System.out.println("Bookings written to file: " + outputFilePath);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

上述代码将预订信息从文件中读取到字符串数组中，然后将其写入输出文件。请注意，我们使用BufferedReader和BufferedWriter来进行文件的读写，以提高效率。同时，我们还在输出文件中添加了一个新行符。