Java, assert file equals

Question

I want assert to files using char by char comparation. What the best way to do this? Without 3rd part libraries. Which file-reader is most performance for this?

How big are the files? If they are small enough then simply loading them into memory and comparing the `byte[]` with the appropriate assertion tools would probably be the easiest way. If they can be larger, then that won't work, of course. — Joachim Sauer, May 25 '12 at 08:33
That should easily fit in memory. Note: two files can have different bytes, but have exactly the same characters. ;) — Peter Lawrey, May 25 '12 at 08:51
And since the post is tagged with 'performance': on Java 7 you should possibly check both are the same size prior to reading (if I'm not wrong java.nio.file.Files.size(...) was introduced in Java 7). — Axel, May 25 '12 at 09:13

score 14 · Accepted Answer · answered May 25 '12 at 08:32

14

Not sure what the objection to 3rd party libraries is... no need to re-invent the wheel.

I've found the open-source and widely used apache.commons.io method FileUtils.contentEquals(file1, file2) is pretty good - here's the javadoc.

answered May 25 '12 at 08:32

amaidment

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is there a java 7 implementation for this function? – Thomas Jan 03 '15 at 22:38
@Thomas - no. Java 7 had been out for almost a year when this question was asked, and as the answer indicates, this requires a 3rd party library. – amaidment Jan 06 '15 at 18:55

Andrejs · Answer 2 · 2015-12-21T16:27:55.107

2

If you happen to be using Google Guava library then you can use:

Files.equal(file1, file2);

From the docs:

Returns true if the files contains the same bytes.

edited Dec 21 '15 at 16:27

answered Mar 09 '14 at 20:27

Andrejs

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There is no [equals](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/io/Files.html). – wener Dec 19 '15 at 18:52
@wener Fixed, it was `equal` – Andrejs Dec 21 '15 at 16:28

score 1 · Answer 3 · answered Dec 21 '15 at 16:40

For small files (up to a few MB), streaming I/O will yield little benefit, so you might keep things simple:

Arrays.equals(Files.readAllBytes(firstFile), Files.readAllBytes(secondFile));

If you want to use different encodings, you can also decode the bytes into characters:

boolean equal = new String(Files.readAllBytes(firstFile), firstEncoding).equals(
                new String(Files.readAllBytes(secondFile), secondEncoding));

This only requires Java 7.

Java, assert file equals

3 Answers3