Java APIs for Text file comparison

[Nisha Soorya]

Is there any java API available for comparint two text files?

What I want to do is to implement the compare functionality (as in TextPad) in Java Swing. Compare, and display the changes with a different color or highlight.

Any suggestion will be greatly appreciated. If APIs are not available please advice me how to do this.

Thanks,
Nisha

[Ulf Dittmer]

A library I've been using is jlibdiff. It's a basic framework for comparing 2 (or even 3) files, but not well-documented. When I searched for something better with a Java API, I came up with nothing. You may have more luck running the "diff" tool directly (via Runtime.exec), and interpret the results in your application.

[Nisha Soorya]

Thanks for your reply. Actually the solution I was looking for is exactly like the sample application provided with jlibdiff. But I have to incorporate the same functionality into another swing application.

But without any documentation, I don't know if can possible to use the same. The only document provided with that is in French. :-( .

My application needs to be executed in Windows. So I can't use diff.

[Ulf Dittmer]

My application needs to be executed in Windows. So I can't use diff.

If you can install stuff on the machine, have a look at unxutils, which provides many of the standard Unix tools on Windows.

[Dale Seng]

You can use WinDiff from the NT tools disk from Microsoft after writing the two files to file. That's what I did anyway. I created a batch file that called my Java code that created the two files, then it went on to start windiff when my code ended.

Mine was a very quick and dirty app, but if you figure something out (find something on sourceforge, or make it yourself), I'd be interested in the source.

--Dale--

[Stan James]

Here's a TextDiff I adapted from something on the web. Here's some of the doc:

TextDiff compares two text files or arrays of strings and generates a report of edit commands that would transform Old to New.

The DefaultReportWriter prints a human-friendly report to a PrintStream such as System.out. One could implement custom report writers to create machine-readable reports such as concrete editor commands.

Usage:

Report report = new TextDiff().compare( oldFileName, newFileName );
report.print( );

[ June 28, 2006: Message edited by: Stan James ]

[Ulf Dittmer]

Stan, that's interesting stuff. The test programs use the com.saxman.util.SSString class - do you know where that is available? Or does SSString.arrayToString exactly what its name implies?

[Stan James]

Oops, forgot that gem was referenced in there. It's rather a monster with zillions of string functions and just about the first thing I wrote in Java so maybe I won't share the whole thing.

I use delimited strings with the delimiter first. That way you can use any delimiter you like, and even nest delimited strings with different delimiters. ArrayToString() has a list of candidate delimiters and finds one that is not in the data. Here's a bit of the unit tests:

public void testStringToArray()
{
    String[] expect = new String[] { "one", "two", "three" };
    String[] result = SSString.stringToArray("/one/two/three/");
    assertEquals(expect, result);
 
    expect = new String[] { "one", "", "three" };
    result = SSString.stringToArray("/one//three/");
    assertEquals(expect, result);
 
    expect = new String[] { "one", "", "", "", "five" };
    result = SSString.stringToArray("/one////five/");
    assertEquals(expect, result);
}
public void testArrayToString()
{
    assertEquals("/one/two/three/", SSString.arrayToString(new String[] { "one", "two", "three" }));
    assertEquals("/one//three/", SSString.arrayToString(new String[] { "one", "", "three" }));
}

Oh, yeah, there's a custom assertEquals() in there for two string arrays, too.

[ June 29, 2006: Message edited by: Stan James ]
[ June 29, 2006: Message edited by: Stan James ]

[Ulf Dittmer]

Thanks Stan.

Now that I'm ready to get into it, I noticed that it also needs the com.saxman.util.TextFileIn class, which is not part of the download. Could I trouble you to make that available as well?

[Stan James]

TextFileIn is even older than SSString, truly one of the first things I did in Java, largely borrowed from something in TIJ I think. I'm too embarrased to read it but here it is ...

package com.saxman.util;
 
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
/**
 * This class represents a text file input from disk.  Usage:
 * <pre>
 * TextFileIn MyFileIn = new TextFileIn( fileid );
 * while ( ( MyLine = MyFileIn.readLine() ) != null )
 * {
 *    do something with MyLine
 * }
 * </pre>
 * Note: No close is necessary if you read to end of file.  If
 * you do not read to end of file, call close().
 */
public class TextFileIn
{
    private BufferedReader mReader = null;
    /**
     * Default constructor is private. Use constructor with FileName.
     */
    private TextFileIn()
    {
    }
    /**
     * Constructor opens named file for input.
     * @param aFileName java.lang.String
     */
    public TextFileIn(String aFileName) throws java.io.FileNotFoundException
    {
        mReader = new BufferedReader(new FileReader(aFileName));
    }
    /**
     * Constructor opens provided file for input.
     * @param aFile
     */
    public TextFileIn(File aFile) throws FileNotFoundException
    {
        mReader = new BufferedReader(new FileReader(aFile));
    }
    /**
     * Returns contents of a file as one string.  NewLine characters that
     * delimit lines in the file are converted to single spaces.
     * <p>
     * 09/26/2000 Standley New
     * @return String
     */
    public String asString() throws java.io.IOException
    {
        String lLine;
        StringBuffer lReturn = new StringBuffer();
 
        while ((lLine = this.readLine()) != null)
        {
            lReturn.append(lLine);
            lReturn.append(" ");
        }
        return lReturn.toString();
    }
    /**
     * Returns contents of a file as an array of Strings.
     * @return String[]
     */
    public String[] asArray() throws IOException
    {
        String lLine;
        List lList = new ArrayList();
        while (null != (lLine = this.readLine()))
        {
            lList.add(lLine);
        }
        return (String[])lList.toArray(new String[] {});
    }
    /**
     * Close the input file.  This is not necessary if the client
     * reads to end of file.
     * <p>11/14/00 JLS Made close on closed file not an error.
     */
    public void close()
    {
        if (null == mReader)
            return;
        try
        {
            mReader.close();
            mReader = null;
        }
        catch (Exception e)
        {
        }
    }
    /**
     * Main for testing - demonstrates common usage.
     * @param args java.lang.String[]
     */
    public static void main(String[] args)
    {
        String lLine;
        try
        {
            TextFileIn lFile = new TextFileIn("c:\\test.dat");
            while ((lLine = lFile.readLine()) != null)
            {
                System.out.println(lLine);
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
    /**
     * Read one line from input file.  On read past end of file
     * closes the file and returns null.
     * @return java.lang.String
     */
    public String readLine() throws java.io.IOException
    {
        if (null == mReader)
            throw new java.io.IOException();
        String lLine = mReader.readLine();
        if (null == lLine)
            this.close();
        return lLine;
    }
}

[Ulf Dittmer]

Now everything compiles fine - Thanks Stan!

Now I just need to figure out how it works, and how to replace jlibdiff with it - but that's the fun part
[ July 08, 2006: Message edited by: Ulf Dittmer ]

[Stan James]

Let me know if you fix any defects in that. If you're really going to use it for more than an educational example I'll look into my work baseline and see if I fixed any, too.

[David W Brown]

Hello, I know this is somewhat dated material but I was in the throes of a project and related solutions at my job when I have mavenized the TextDiff solution. If anyone is interested I can put this somewhere on the net. I have a blog that I have up-and-running but I have held off on putting any content on the blog. If there is any interest I can put the mavenized TextDiff files there such that folks can download TextDiff from the blog. Please advise, David.

[Campbell Ritchie]

Thank you. I thought it was dated; Stan James died at the end of 2007.

Probably best to quote a link to your material here, please. Then anybody interested can look it up.

[Ulf Dittmer]

David, I'd be very interested in that.

[Tim gae]

Hello,

We are now in 2010 and I'would like to know if there are new libraries that can compare two texts and see their differences.

thank you,

PS: I have used jlibdiff, htmlDiff but they seem abandoned.

[Tim gae]

Up

[Rob Spoor]

Tim gae wrote:PS: I have used jlibdiff, htmlDiff but they seem abandoned.

Is that a bad thing? I have one application on SourceForge which hasn't been updated since May 2007, simply because I consider it to be ready.

[Tim gae]

Yes you are right but the problem is that I have no documentation for use.

[J J Wright]

http://code.google.com/p/google-diff-match-patch/