Tezen Tezen - 2 months ago 8
Java Question

java copying input to multiple output files

I am trying to copy the contents of an inputFile to multiple other files. I am trying to do this using command line arguments.

However, I am having some difficulties with the closing of the printwriter. I don't know where or how i should do it. If i do it in my for-loop, the content only gets copied to one output file. I tried an if-statement but that didn't work either. If I close it outside of the for-loop. I get a 'cannot find symbol error' which makes sense since I declared it inside the for-loop.

My question thus is: How and where am I supposed to close the printwriter in this situation?

Thank you in advance.

import java.util.*;
import java.io.*;
public class try13 {
public static void main(String[] args) throws FileNotFoundException {
File inputFile = new File(args[0]);
Scanner in = new Scanner(inputFile);
for(int i = 1; i < args.length; i++) {
PrintWriter out = new PrintWriter(args[i]);
while (in.hasNextLine()) {
String line = in.nextLine();
out.println(line);
}
}
in.close();
out.close();
}
}

Answer

First make an array of the PrintWriters, then copy each line read from the input to all of the outputs:

import java.util.*;
import java.io.*;
public class try13 {
    public static void main(String[] args) throws FileNotFoundException {
        File inputFile = new File(args[0]);
        Scanner in = new Scanner(inputFile);

        /* Create all the writers and put then in a list */
        List<PrintWriter> writers = new ArrayList<>();
        for(int i = 1; i < args.length; i++) {
            writers.add(new PrintWriter(args[i]));
        }

        /* Read each line and write it to all writers */
        while (in.hasNextLine()) {
            String line = in.nextLine();
            writers.forEach(writer -> writer.println(line));
        }

        in.close();

        /* Close all the writers */
        writers.forEach(writer -> {
                try {
                    writer.close();
                } catch(Exception e) {}
        });
    }
}

If you are not using Java8, try this:

/* Read each line and write it to all writers */
while (in.hasNextLine()) {
    String line = in.nextLine();
    for(PrintWriter writer : writers) {
        writer.println(line);
    }
}

... and this:

/* Close all the writers */
for(PrintWriter writer : writers) {
    try {
        writer.close();
    } catch(Exception e) {}
}
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