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Maven 3: How Version Comparison Works?

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In the ancient time before maven 3 the version of an artifact had to follow the pattern:

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<majorversion [> . <minorversion [> . <incrementalversion ] ] [> - <buildnumber | qualifier ]>

so far so good. Now let us assume we have the following two versions:

  • 1.0.9.3.1
  • 1.0.10.11

What would you expect which version is newer than the other or the older one? I suppose you would say: 1.0.9.3.1 is older than 1.0.10.11 or with other words: 1.0.10.11 is newer than 1.0.9.3.1 or to express it in a more mathematical way:

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1.0.9.3.1 < 1.0.10.11

Or another example:

  • 1.0alpha10
  • 1.0alpha2

So I assume that you have expected that Maven 2 should have handled that like this:

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1.0alpha10 > 1.0alpha2

Unfortunately Maven 2 had handled them different because the previous versions did not follow the above pattern which results into string based comparison of the versions and finally into the following result:

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1.0.9.3.1 > 1.0.10.11
1.0alpha10 < 1.0alpha2

which is obviously not the result you have expected.

Maven 3

Starting with Maven 3 (released 2010!) the version comparison has been changed but unfortunately the above myth keeps tenaciously.

So the first thing is that you can use as many digits as you like and separate them by dots. This means the following versions are valid:

Version Version
2 1
1.1 1.0
1.2.3 1.2.1
1.2.3.4 1.2.2.4
1.4.5.7.9 1.4.5.60.9
1.2.30.4.5 1.2.2.4.5
1.0.10.11 1.0.9.3.1
1.0alpha10 1.0alpha2
1.0 1.0.0

Regarding the above list which version is mathematically greater, greater or equal, less than, less or equal than the other?

Version Version
2 > 1
1.1 > 1.0
1.2.3 > 1.2.1
1.2.3.4 > 1.2.2.4
1.4.5.7.9 < 1.4.5.60.9
1.2.30.4.5 > 1.2.2.4.5
1.0.10.11 > 1.0.9.3.1
1.0alpha10 > 1.0alpha2
1.0 = 1.0.0

So what about things like 1.6.0-RC1 ? Let us assume we have the following versions:

  • 1.6.0
  • 1.6.0-RC1

So how does the comparison result look like? If you think a little you might already know the solution. The 1.6.0-RC1 is of course older than 1.6.0 or expressed mathematically:

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1.6.0-RC1 < 1.6.0

This is because a release candidate is created before the final 1.6.0 release. So other things could be concluded out of the above like this:

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1.6.0-RC3 < 1.6.0-RC10 < 1.6.0
2.34.5.6-RC3 < 2.34.5.6-RC10 < 2.34.5.6

So what about things like milestones: 1.6.0-m1?

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1.6.0-m1 < 1.6.0 

which is this way based on the assumption made above. Milestones are before the final releases. So of course you can conclude ordering of milestones like this:

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1.6.0-m1 < 1.6.0-m4
1.6.0-m4 < 1.6.0-m10

The above is also valid for the cases where we separate the milestone via a dot instead of a dash.

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1.6.0.m1 < 1.6.0.m4
1.6.0.m4 < 1.6.0.m10

You can do things like the following if you like:

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1.6.0-m1.9.9.11 < 1.6.0-m1.9.10.11

So now we come to an important thing, if we compare the following two versions 1.6.0-m1 with 1.6.0.m1. On the first glance you might think those two versions are equal because they describe a milestone with the same version 1.6.0. The result of the comparison in Maven is different:

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1.6.0-m1 < 1.6.0.m1

This means in consequence that a part which is separated via - is less important than a part wich is separated via ., or the part which is separated via . has precedence over the part which is separated via -.

Snapshots

We have only considered releases yet. So now let us take a look at SNAPSHOTs. So let us try to see which version is before the other one in case of such version 1.6.0-SNASPHOT and 1.6.0.m1? So you might already know the result. The SNAPSHOT version is before the other one 1.6.0.m1 cause a SNAPSHOT means there has no release before of 1.6.0.

You can add the -SNAPSHOT part to each of the above examples but the results will keep the same.

Experiments

If you like to experiment with some of the above examples or check your ideas you can simply use your existing(?) Maven installation for this. Starting with Maven 3.2.5 there is a command line interface which can show you the comparision results for versions given on the command line like this:

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java -jar apache-maven-3.2.5/lib/maven-artifact-3.2.5.jar 1.6.0 1.6.0.m1

The output will look similar like this:

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Display parameters as parsed by Maven (in canonical form) and comparison result:
1. 1.6.0 == 1.6
   1.6.0 > 1.6.0-rc1
2. 1.6.0-rc1 == 1.6-rc-1

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