Question

I asked a similar question before regarding I/O using Java.

I’m trying to copy a list of strings into another file.

package file;

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

public class File {

    public static void main(String[] args) {

                FileWrite fW = new FileWrite();

                try (BufferedReader br = new BufferedReader(new FileReader("B:\\inLarge.dat")))
        {

            String stCurrent;

            while ((stCurrent = br.readLine()) != null) {
                System.out.println(stCurrent);
                                fW.serializeAddress(stCurrent, stCurrent);
            }

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


                //fW.serializeAddress("Boston", "Canada");
    }
}

And

package file;

import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.ObjectOutputStream;
import java.io.PrintStream;
import java.io.Serializable;
import java.io.File;
import java.io.IOException;

public class FileWrite {

   public void serializeAddress(String city, String country){

       try
           {

               File file = new File("B:\\outLarge.txt");

               if (!file.exists()) 
                        {
                file.createNewFile();
            }

               FileWriter fw = new FileWriter(file.getAbsoluteFile());
               BufferedWriter bw = new BufferedWriter(fw);
               bw.write(city + " " + country);
               bw.close();

            System.out.println("Done");



       }
           catch(Exception ex)
           {
           ex.printStackTrace();
       }
   }
}

But the ending output file has only one result, how do I make it copy everything?
I am thinking buffered-writer somehow needs to be in the loop to write new ones on top of existing ones? But not sure how to implement that.

Thanks a lot.

Answer 1

You are overwriting the file contents every time you call your serialize method, because you didn’t open the file in append mode. To prevent overwriting, open the file in append mode:

FileWriter fw = new FileWriter(file.getAbsoluteFile(), true);

However, this is one case where the solution is probably over-engineered. For efficiency you really should be opening your file just once. Here’s an example:

public static void main(final String[] args) {
    try {
        final BufferedReader reader = new BufferedReader(new FileReader("infile.txt"));
        final PrintWriter writer = new PrintWriter(new File("outfile.txt"));

        String inputLine;

        while((inputLine = reader.readLine()) != null) {
            writer.println(inputLine);
        }

        reader.close();
        writer.close();
    } catch(final Exception e) {
        e.printStackTrace();
    }
}