Split files in java

Question

I have a program to split .txt files that divides it in 101 files. The file that must be divided File.txt contains url separated by \n. The fact is that the program divides the file in equal parts and when it reaches the maximum size it cuts the url and starts a new file. How can I do to split it in a size that don't overshoot 1Mb and contains the url well splited?

import java.io.*;
import java.util.Scanner;

public class readfile {
    public static int SubfileName;
    public static int[] Murl = new int[2000000];
    public static int x = 0;
    public static long usemem = 0;
    public static long Numberofmailto = 0;
    static byte[] subfich; //Subfile data (global var)
    static long NumberUrl;
    static int[] indURL; //Indices de las URLs en "subfich"

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter the file name like url.txt to read but it should be in E:\\url\\");
        String name = in.nextLine();
        readfile(name);

        try {
            //now create 100 subfile 
            GeneraFicheros();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    // not used 
    public static void readfile(String filename) {
        try {
            // file path
            leeSubfichero("E:\\url\\" + filename);

            creaIndices();
        } catch (Exception e) {
        }
    }

    //read danger file
    static void leeSubfichero(String nomfich) throws IOException { // read file
        File fich = new File(nomfich);
        int tam = (int) fich.length(); //Tamaño bytes // size byte
        subfich = null;
        subfich = new byte[tam];
        try (FileInputStream fis = new FileInputStream(fich)) {
            NumberUrl = fis.read(subfich);
            // find the mailto urls
        }
    }


    static void creaIndices() {
        // 1. Count the number of URLs
        int n = 0;
        int x = 0;
        boolean dangerurl = false;
        for (int i = 0; i < subfich.length; i++) {
            if (subfich[i] == 10) {
                n++;
            }
        }

        //2. Store separators position
        indURL = null;
        indURL = new int[n];
        //Murl = new int[n];
        int k = 0;
        for (int i = 0; i < subfich.length; i++) {
            if (subfich[i] == 10) {
                indURL[k++] = i;
            }
        }
    }

    // create 100 files
    public static void GeneraFicheros() throws Exception {
        String zero = "00";
        RandomAccessFile raf = new RandomAccessFile("E:\\url\\danger.txt", "r");
        long numSplits = 100; //divid in 100 subfiles
        long sourceSize = raf.length();  // danger.txt file size
        long bytesPerSplit = sourceSize / numSplits; // number of bytes each file will have
        long remainingBytes = sourceSize % numSplits;

        int maxReadBufferSize = 8 * 1024; //8KB
        for (int destIx = 1; destIx <= numSplits; destIx++) {
            // each literation create a new file like 000 
            System.out.println("Escrito Subfichero " + zero + destIx + ".txt");
            runtime();
            if (destIx > 9) {
                zero = "0";
            }

            // write the file with name like 000.txt
            BufferedOutputStream bw = new BufferedOutputStream(new FileOutputStream("E:\\url\\" + zero + destIx + ".txt"));
            if (bytesPerSplit > maxReadBufferSize) {
                // total number of bytes to read
                long numReads = bytesPerSplit / maxReadBufferSize;
                // total number of bytes remaining for other files
                long numRemainingRead = bytesPerSplit % maxReadBufferSize;
                for (int i = 0; i < numReads; i++) {
                    readWrite(raf, bw, maxReadBufferSize);
                }
                // if bytes are remaining write the file
                if (numRemainingRead > 0) {
                    readWrite(raf, bw, numRemainingRead);
                }
            } else {
                readWrite(raf, bw, bytesPerSplit);
            }
            bw.close();
        }
        // if dividion didn't work extra store here 
        if (remainingBytes > 0) {
            BufferedOutputStream bw = new BufferedOutputStream(new FileOutputStream("split." + (numSplits + 1) + ".txt"));
            readWrite(raf, bw, remainingBytes);
            bw.close();
        }
        raf.close();
    }


    // write 8kb each time in the file
    static void readWrite(RandomAccessFile raf, BufferedOutputStream bw, long numBytes) throws IOException {
        byte[] buf = new byte[(int) numBytes];
        int val = raf.read(buf);
        if (val != -1) {
            bw.write(buf);
        }
    }

    static long startTime = System.nanoTime();

    public static void runtime() {
        long endTime = System.nanoTime();
        long totalTime = endTime - startTime;
        double seconds = (double) totalTime / 1000000000.0;
        System.out.println("Toatl seconds" + seconds);
    }
}

Are you trying to split the file into 101 parts of equal size or do you want to split it into files not exceeding 1 MB? — daniu, Oct 08 '18 at 11:23
I want to split into files not exceding 1Mb. It is not needed that the files have the same size — PowerRangerPoint69, Oct 08 '18 at 11:26
Meanwhile, you want to achieve limiting the size of a file? Then check the correct answer on https://stackoverflow.com/questions/39092861/limit-file-size-while-writing-in-java — Kumar Panchal, Oct 08 '18 at 11:30
Better: but please remove all these pointless empty lines. Code is written for human readers. — GhostCat, Oct 08 '18 at 11:36

score 4 · Answer 1 · answered Oct 08 '18 at 11:25

There's no way to do this job, the way you've set up the code. Your code is fundamentally based on bytes (which makes it impossible to read something like a newline character, which is a character, not a byte), and it 'precalculates' how much to read, which also makes it impossible. Imagine there's a URL in your input file that is really long; almost as long as the required size.

Finally, there's no feasible way to say: "Split this file into exactly 100 parts, but do it in a way that EVERY file is smaller than totalsize/100... and also don't cut any lines in half." – there will probably be 101 files, there might even be 250 files. There might also be only 1 file, if the entire file is just one very long URL.

You'd have to specify exactly what you want your program to do before writing it.

Some tips:

Use Files.newBufferedReader, passing in the charset. You need to move away from InputStream because that's for bytes, not characters.
Read an entire line into memory, then and only then decide whether this line can be added to the current 'segment' you're writing, or if you need to make a new one because otherwise the segment you're writing would become too large.

Split files in java

1 Answers1