A very big file

Question

i have a very big text file . almost 800 MB . in some lines i have a special pattern "from the end" is present. i want to pick up those lines.
whats are the possible efficient solutions ?
as the file is large , i hesitate to use BufferedReader + readLine + indexOf("from the end") because its not efficient . it reads all the lines.
is RandomAccessFle will be a good solution ? but RAF dont have readLine + indexOf("from the end") .how do i solve it then ?
i have java 1.4 . in java 1.4 what is the best solution for solving this kind of problem ?

Answer 1

Under all circumstance you'll have to read all bytes
of the file once.Not true! If the file consists of bytes with a character representation that uses only one byte (e.g. ASCII or iso-8859-x) then the following class if very efficient.
import java.io.*;
import java.util.*;
public class GetLinesFromEndOfFile
    static public class BackwardsFileInputStream extends InputStream
        public BackwardsFileInputStream(File file) throws IOException
            assert (file != null) && file.exists() && file.isFile() && file.canRead();
            raf = new RandomAccessFile(file, "r");
            currentPositionInFile = raf.length();
            currentPositionInBuffer = 0;
        public int read() throws IOException
            if (currentPositionInFile <= 0)
                return -1;
            if (--currentPositionInBuffer < 0)
                currentPositionInBuffer = buffer.length;
                long startOfBlock = currentPositionInFile - buffer.length;
                if (startOfBlock < 0)
                    currentPositionInBuffer = buffer.length + (int)startOfBlock;
                    startOfBlock = 0;
                raf.seek(startOfBlock);
                raf.readFully(buffer, 0, currentPositionInBuffer);
                return read();
            currentPositionInFile--;
            return buffer[currentPositionInBuffer];
        public void close() throws IOException
            raf.close();
        private final byte[] buffer = new byte[4096];
        private final RandomAccessFile raf;
        private long currentPositionInFile;
        private int currentPositionInBuffer;
    public static List<String> head(File file, int numberOfLinesToRead) throws IOException
        return head(file, "ISO-8859-1" , numberOfLinesToRead);
    public static List<String> head(File file, String encoding, int numberOfLinesToRead) throws IOException
        assert (file != null) && file.exists() && file.isFile() && file.canRead();
        assert numberOfLinesToRead > 0;
        assert encoding != null;
        LinkedList<String> lines = new LinkedList<String>();
        BufferedReader reader= new BufferedReader(new InputStreamReader(new FileInputStream(file), encoding));
        for (String line = null; (numberOfLinesToRead-- > 0) && (line = reader.readLine()) != null;)
            lines.addLast(line);
        reader.close();
        return lines;
    public static List<String> tail(File file, int numberOfLinesToRead) throws IOException
        return tail(file, "ISO-8859-1" , numberOfLinesToRead);
    public static List<String> tail(File file, String encoding, int numberOfLinesToRead) throws IOException
        assert (file != null) && file.exists() && file.isFile() && file.canRead();
        assert numberOfLinesToRead > 0;
        assert (encoding != null) && encoding.matches("(?i)(iso-8859|ascii|us-ascii).*");
        LinkedList<String> lines = new LinkedList<String>();
        BufferedReader reader= new BufferedReader(new InputStreamReader(new BackwardsFileInputStream(file), encoding));
        for (String line = null; (numberOfLinesToRead-- > 0) && (line = reader.readLine()) != null;)
            // Reverse the order of the characters in the string
            char[] chars = line.toCharArray();
            for (int j = 0, k = chars.length - 1; j < k ; j++, k--)
                char temp = chars[j];
                chars[j] = chars[k];
                chars[k]= temp;
            lines.addFirst(new String(chars));
        reader.close();
        return lines;
    public static void main(String[] args)
        try
            File file = new File("/usr/share/dict/words");
            int n = 10;
                System.out.println("Head of " + file);
                int index = 0;
                for (String line : head(file, n))
                    System.out.println(++index + "\t[" + line + "]");
                System.out.println("Tail of " + file);
                int index = 0;
                for (String line : tail(file, "us-ascii", n))
                    System.out.println(++index + "\t[" + line + "]");
        catch (Exception e)
            e.printStackTrace();
}