How can I normalize the EOL character in Java?

Question

I have a linux server and many clients with many operating systems. The server takes an input file from clients. Linux has end of line char LF, while Mac has end of line cha

Answer 1

Here is a comprehensive helper class to deal with EOL issues. It it partially based on the solution posted by tyjen.

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;

/**
 * Helper class to deal with end-of-line markers in text files.
 * 
 * Loosely based on these examples:
 *  - http://stackoverflow.com/a/9456947/1084488 (cc by-sa 3.0)
 *  - http://svn.apache.org/repos/asf/tomcat/trunk/java/org/apache/tomcat/buildutil/CheckEol.java (Apache License v2.0)
 * 
 * This file is posted here to meet the "ShareAlike" requirement of cc by-sa 3.0:
 *    http://stackoverflow.com/a/27930311/1084488
 * 
 * @author Matthias Stevens
 */
public class EOLUtils
{

    /**
     * Unix-style end-of-line marker (LF)
     */
    private static final String EOL_UNIX = "\n";

    /**
     * Windows-style end-of-line marker (CRLF)
     */
    private static final String EOL_WINDOWS = "\r\n";

    /**
     * "Old Mac"-style end-of-line marker (CR)
     */
    private static final String EOL_OLD_MAC = "\r";

    /**
     * Default end-of-line marker on current system
     */
    private static final String EOL_SYSTEM_DEFAULT = System.getProperty( "line.separator" );

    /**
     * The support end-of-line marker modes
     */
    public static enum Mode
    {
        /**
         * Unix-style end-of-line marker ("\n")
         */
        LF,

        /**
         * Windows-style end-of-line marker ("\r\n") 
         */
        CRLF,

        /**
         * "Old Mac"-style end-of-line marker ("\r")
         */
        CR
    }

    /**
     * The default end-of-line marker mode for the current system
     */
    public static final Mode SYSTEM_DEFAULT = ( EOL_SYSTEM_DEFAULT.equals( EOL_UNIX ) ? Mode.LF : ( EOL_SYSTEM_DEFAULT
        .equals( EOL_WINDOWS ) ? Mode.CRLF : ( EOL_SYSTEM_DEFAULT.equals( EOL_OLD_MAC ) ? Mode.CR : null ) ) );
    static
    {
        // Just in case...
        if ( SYSTEM_DEFAULT == null )
        {
            throw new IllegalStateException( "Could not determine system default end-of-line marker" );
        }
    }

    /**
     * Determines the end-of-line {@link Mode} of a text file.
     * 
     * @param textFile the file to investigate
     * @return the end-of-line {@link Mode} of the given file, or {@code null} if it could not be determined
     * @throws Exception
     */
    public static Mode determineEOL( File textFile )
        throws Exception
    {
        if ( !textFile.exists() )
        {
            throw new IOException( "Could not find file to open: " + textFile.getAbsolutePath() );
        }

        FileInputStream fileIn = new FileInputStream( textFile );
        BufferedInputStream bufferIn = new BufferedInputStream( fileIn );
        try
        {
            int prev = -1;
            int ch;
            while ( ( ch = bufferIn.read() ) != -1 )
            {
                if ( ch == '\n' )
                {
                    if ( prev == '\r' )
                    {
                        return Mode.CRLF;
                    }
                    else
                    {
                        return Mode.LF;
                    }
                }
                else if ( prev == '\r' )
                {
                    return Mode.CR;
                }
                prev = ch;
            }
            throw new Exception( "Could not determine end-of-line marker mode" );
        }
        catch ( IOException ioe )
        {
            throw new Exception( "Could not determine end-of-line marker mode", ioe );
        }
        finally
        {
            // Clean up:
            IOUtils.closeQuietly( bufferIn );
        }
    }

    /**
     * Checks whether the given text file has Windows-style (CRLF) line endings.
     * 
     * @param textFile the file to investigate
     * @return
     * @throws Exception
     */
    public static boolean hasWindowsEOL( File textFile )
        throws Exception
    {
        return Mode.CRLF.equals( determineEOL( textFile ) );
    }

    /**
     * Checks whether the given text file has Unix-style (LF) line endings.
     * 
     * @param textFile the file to investigate
     * @return
     * @throws Exception
     */
    public static boolean hasUnixEOL( File textFile )
        throws Exception
    {
        return Mode.LF.equals( determineEOL( textFile ) );
    }

    /**
     * Checks whether the given text file has "Old Mac"-style (CR) line endings.
     * 
     * @param textFile the file to investigate
     * @return
     * @throws Exception
     */
    public static boolean hasOldMacEOL( File textFile )
        throws Exception
    {
        return Mode.CR.equals( determineEOL( textFile ) );
    }

    /**
     * Checks whether the given text file has line endings that conform to the system default mode (e.g. LF on Unix).
     * 
     * @param textFile the file to investigate
     * @return
     * @throws Exception
     */
    public static boolean hasSystemDefaultEOL( File textFile )
        throws Exception
    {
        return SYSTEM_DEFAULT.equals( determineEOL( textFile ) );
    }

    /**
     * Convert the line endings in the given file to Unix-style (LF).
     * 
     * @param textFile the file to process
     * @throws IOException
     */
    public static void convertToUnixEOL( File textFile )
        throws IOException
    {
        convertLineEndings( textFile, EOL_UNIX );
    }

    /**
     * Convert the line endings in the given file to Windows-style (CRLF).
     * 
     * @param textFile the file to process
     * @throws IOException
     */
    public static void convertToWindowsEOL( File textFile )
        throws IOException
    {
        convertLineEndings( textFile, EOL_WINDOWS );
    }

    /**
     * Convert the line endings in the given file to "Old Mac"-style (CR).
     * 
     * @param textFile the file to process
     * @throws IOException
     */
    public static void convertToOldMacEOL( File textFile )
        throws IOException
    {
        convertLineEndings( textFile, EOL_OLD_MAC );
    }

    /**
     * Convert the line endings in the given file to the system default mode.
     * 
     * @param textFile the file to process
     * @throws IOException
     */
    public static void convertToSystemEOL( File textFile )
        throws IOException
    {
        convertLineEndings( textFile, EOL_SYSTEM_DEFAULT );
    }

    /**
     * Line endings conversion method.
     * 
     * @param textFile the file to process
     * @param eol the end-of-line marker to use (as a {@link String})
     * @throws IOException 
     */
    private static void convertLineEndings( File textFile, String eol )
        throws IOException
    {
        File temp = null;
        BufferedReader bufferIn = null;
        BufferedWriter bufferOut = null;

        try
        {
            if ( textFile.exists() )
            {
                // Create a new temp file to write to
                temp = new File( textFile.getAbsolutePath() + ".normalized" );
                temp.createNewFile();

                // Get a stream to read from the file un-normalized file
                FileInputStream fileIn = new FileInputStream( textFile );
                DataInputStream dataIn = new DataInputStream( fileIn );
                bufferIn = new BufferedReader( new InputStreamReader( dataIn ) );

                // Get a stream to write to the normalized file
                FileOutputStream fileOut = new FileOutputStream( temp );
                DataOutputStream dataOut = new DataOutputStream( fileOut );
                bufferOut = new BufferedWriter( new OutputStreamWriter( dataOut ) );

                // For each line in the un-normalized file
                String line;
                while ( ( line = bufferIn.readLine() ) != null )
                {
                    // Write the original line plus the operating-system dependent newline
                    bufferOut.write( line );
                    bufferOut.write( eol ); // write EOL marker
                }

                // Close buffered reader & writer:
                bufferIn.close();
                bufferOut.close();

                // Remove the original file
                textFile.delete();

                // And rename the original file to the new one
                temp.renameTo( textFile );
            }
            else
            {
                // If the file doesn't exist...
                throw new IOException( "Could not find file to open: " + textFile.getAbsolutePath() );
            }
        }
        finally
        {
            // Clean up, temp should never exist
            FileUtils.deleteQuietly( temp );
            IOUtils.closeQuietly( bufferIn );
            IOUtils.closeQuietly( bufferOut );
        }
    }

}