CODEWITHSUNDEEP
java
Glory to Russia
Glory to Russia

Reputation: 18712

Java: How to check that 2 binary files are same?

What is the easiest way to check (in a unit test) whether binary files A and B are equal?

Upvotes: 19

Views: 14715

Answers (8)

MaduKan
MaduKan

Reputation: 660

Apache Commons IO solution:

boolean sameFileContent = FileUtils.contentEquals(file1, file2)

From documentation:

Compares the contents of two files to determine if they are equal or not. Checks that

  1. The two files are different lengths or,
  2. If they point to the same file,
  3. And then does a byte-by-byte comparison of the contents.

Reference: https://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/FileUtils.html

Upvotes: 0

Binkan Salaryman
Binkan Salaryman

Reputation: 3048

Read the files in (small) blocks and compare them:

static boolean binaryDiff(File a, File b) throws IOException {
    if(a.length() != b.length()){
        return false;
    }
    
    final int BLOCK_SIZE = 128;
    InputStream aStream = new FileInputStream(a);
    InputStream bStream = new FileInputStream(b);
    byte[] aBuffer = new byte[BLOCK_SIZE];
    byte[] bBuffer = new byte[BLOCK_SIZE];
    do {
        int aByteCount = aStream.read(aBuffer, 0, BLOCK_SIZE);
        bStream.read(bBuffer, 0, BLOCK_SIZE);
        if (!Arrays.equals(aBuffer, bBuffer)) {
            return false;
        }
    }
    while(aByteCount < 0);
    return true;
}

Upvotes: 4

dkatzel
dkatzel

Reputation: 31648

There's always just reading byte by byte from each file and comparing them as you go. Md5 and Sha1 etc still have to read all the bytes so computing the hash is extra work that you don't have to do.

if (file1.length() != file2.length()) {
    return false;
}
    
 try( InputStream in1 = new BufferedInputStream(new FileInputStream(file1));
    InputStream in2 = new BufferedInputStream(new FileInputStream(file2));
 ) {

      int value1, value2;
      do {
           //since we're buffered, read() isn't expensive
           value1 = in1.read();
           value2 = in2.read();
           if(value1 != value2) {
               return false;
           }
      } while(value1 >= 0);
     
 // since we already checked that the file sizes are equal 
 // if we're here we reached the end of both files without a mismatch
 return true;
}

Upvotes: 7

James Mudd
James Mudd

Reputation: 2373

Since Java 12 you could also use the Files.mismatch method JavaDoc. It will return -1L if the files are the same.

Upvotes: 3

Louis Wasserman
Louis Wasserman

Reputation: 198014

Are third-party libraries fair game? Guava has Files.equal(File, File). There's no real reason to bother with hashing if you don't have to; it can only be less efficient.

Upvotes: 15

James Mudd
James Mudd

Reputation: 2373

If you want to avoid dependencies you can do it using quite nicely with Files.readAllBytes and Assert.assertArrayEquals

Assert.assertArrayEquals("Binary files differ", 
    Files.readAllBytes(Paths.get(expectedBinaryFile)), 
    Files.readAllBytes(Paths.get(actualBinaryFile)));

Note: This will read the whole file so it might not be efficient with large files.

Upvotes: 4

almanegra
almanegra

Reputation: 663

With assertBinaryEquals.

public static void assertBinaryEquals(java.io.File expected, java.io.File actual)

http://junit-addons.sourceforge.net/junitx/framework/FileAssert.html

Upvotes: 4

A4L
A4L

Reputation: 17595

I had to do the same in a unit test too, so I used SHA1 hashes to do that, to spare the the calculation of the hashes I check if the files sizes are equal first. Here was my attempt:

public class SHA1Compare {
    private static final int CHUNK_SIZE = 4096;

    public void assertEqualsSHA1(String expectedPath, String actualPath) throws IOException, NoSuchAlgorithmException {
        File expectedFile = new File(expectedPath);
        File actualFile = new File(actualPath);
        Assert.assertEquals(expectedFile.length(), actualFile.length());
        try (FileInputStream fisExpected = new FileInputStream(actualFile);
                FileInputStream fisActual = new FileInputStream(expectedFile)) {
            Assert.assertEquals(makeMessageDigest(fisExpected), 
                    makeMessageDigest(fisActual));
        }
    }

    public String makeMessageDigest(InputStream is) throws NoSuchAlgorithmException, IOException {
        byte[] data = new byte[CHUNK_SIZE];
        MessageDigest md = MessageDigest.getInstance("SHA1");
        int bytesRead = 0;
        while(-1 != (bytesRead = is.read(data, 0, CHUNK_SIZE))) {
            md.update(data, 0, bytesRead);
        }
        return toHexString(md.digest());
    }

    private String toHexString(byte[] digest) {
        StringBuilder sha1HexString = new StringBuilder();
        for(int i = 0; i < digest.length; i++) {
            sha1HexString.append(String.format("%1$02x", Byte.valueOf(digest[i])));
        }
        return sha1HexString.toString();
    }
}

Upvotes: 1

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