Recently I wrote a project with maven, but I have a question about the version in maven pom.xml.
If I write such a dependency
<dependency>
<groupId>foo</groupId>
<artifactId>bar</artifactId>
<!--No version here-->
</dependency>
what will the version be
in a simple project, no subproject
as a dependency in another project and that project use foo-bar-1.0.0
Part 1. of your question: If you don't specify a version there are various different outcomes:
a) you will get an error...
[ERROR] The project org.example:myproject:0.5-SNAPSHOT (D:\src\myproject\pom.xml) has 1 error
[ERROR] 'dependencies.dependency.version' for foo:bar:jar is missing. # line 39, column 14
b) if you have defined the version in the dependency management of the project's parent's pom, then that version is taken. The parent of the project doesn't have to be an enclosing superproject. It can simply be a collection of appropriate definitions.
c) if another dependency of your project also depends on foo:bar, and specifies a version, then that version is taken. Maven 2 has a mechanism called transitive dependencies. If the version of a dependency is not explicitly specified for an artifact, it searches the dependency tree and uses the nearest definition in the tree. If there are two nearest definitions, then the first declaration wins (since maven 2.0.9).
Part 2.: I am not sure, but maybe the transitive dependency mechanism also works that way. But the documentation (as far as I understood it) doesn't mention that case.
But somehow I feel that the second part of your question doesn't make sense: I guess that in order to use an artifact as a dependency, you would have to build it first. So you'd have to know the version of the dependencies well before it is used as a dependency itself.
In Maven, dependencies are usually set up like this:
<dependency>
<groupId>wonderful-inc</groupId>
<artifactId>dream-library</artifactId>
<version>1.2.3</version>
</dependency>
Now, if you are working with libraries that have frequent releases, constantly updating the <version> tag can be somewhat annoying. Is there any way to tell Maven to always use the latest available version (from the repository)?
NOTE:
The mentioned LATEST and RELEASE metaversions have been dropped for plugin dependencies in Maven 3 "for the sake of reproducible builds", over 6 years ago.
(They still work perfectly fine for regular dependencies.)
For plugin dependencies please refer to this Maven 3 compliant solution.
If you always want to use the newest version, Maven has two keywords you can use as an alternative to version ranges. You should use these options with care as you are no longer in control of the plugins/dependencies you are using.
When you depend on a plugin or a dependency, you can use the a version value of LATEST or RELEASE. LATEST refers to the latest released or snapshot version of a particular artifact, the most recently deployed artifact in a particular repository. RELEASE refers to the last non-snapshot release in the repository. In general, it is not a best practice to design software which depends on a non-specific version of an artifact. If you are developing software, you might want to use RELEASE or LATEST as a convenience so that you don't have to update version numbers when a new release of a third-party library is released. When you release software, you should always make sure that your project depends on specific versions to reduce the chances of your build or your project being affected by a software release not under your control. Use LATEST and RELEASE with caution, if at all.
See the POM Syntax section of the Maven book for more details. Or see this doc on Dependency Version Ranges, where:
A square bracket ( [ & ] ) means "closed" (inclusive).
A parenthesis ( ( & ) ) means "open" (exclusive).
Here's an example illustrating the various options. In the Maven repository, com.foo:my-foo has the following metadata:
<?xml version="1.0" encoding="UTF-8"?><metadata>
<groupId>com.foo</groupId>
<artifactId>my-foo</artifactId>
<version>2.0.0</version>
<versioning>
<release>1.1.1</release>
<versions>
<version>1.0</version>
<version>1.0.1</version>
<version>1.1</version>
<version>1.1.1</version>
<version>2.0.0</version>
</versions>
<lastUpdated>20090722140000</lastUpdated>
</versioning>
</metadata>
If a dependency on that artifact is required, you have the following options (other version ranges can be specified of course, just showing the relevant ones here):
Declare an exact version (will always resolve to 1.0.1):
<version>[1.0.1]</version>
Declare an explicit version (will always resolve to 1.0.1 unless a collision occurs, when Maven will select a matching version):
<version>1.0.1</version>
Declare a version range for all 1.x (will currently resolve to 1.1.1):
<version>[1.0.0,2.0.0)</version>
Declare an open-ended version range (will resolve to 2.0.0):
<version>[1.0.0,)</version>
Declare the version as LATEST (will resolve to 2.0.0) (removed from maven 3.x)
<version>LATEST</version>
Declare the version as RELEASE (will resolve to 1.1.1) (removed from maven 3.x):
<version>RELEASE</version>
Note that by default your own deployments will update the "latest" entry in the Maven metadata, but to update the "release" entry, you need to activate the "release-profile" from the Maven super POM. You can do this with either "-Prelease-profile" or "-DperformRelease=true"
It's worth emphasising that any approach that allows Maven to pick the dependency versions (LATEST, RELEASE, and version ranges) can leave you open to build time issues, as later versions can have different behaviour (for example the dependency plugin has previously switched a default value from true to false, with confusing results).
It is therefore generally a good idea to define exact versions in releases. As Tim's answer points out, the maven-versions-plugin is a handy tool for updating dependency versions, particularly the versions:use-latest-versions and versions:use-latest-releases goals.
Now I know this topic is old, but reading the question and the OP supplied answer it seems the Maven Versions Plugin might have actually been a better answer to his question:
In particular the following goals could be of use:
versions:use-latest-versions searches the pom for all versions
which have been a newer version and
replaces them with the latest
version.
versions:use-latest-releases searches the pom for all non-SNAPSHOT
versions which have been a newer
release and replaces them with the
latest release version.
versions:update-properties updates properties defined in a
project so that they correspond to
the latest available version of
specific dependencies. This can be
useful if a suite of dependencies
must all be locked to one version.
The following other goals are also provided:
versions:display-dependency-updates scans a project's dependencies and
produces a report of those
dependencies which have newer
versions available.
versions:display-plugin-updates scans a project's plugins and
produces a report of those plugins
which have newer versions available.
versions:update-parent updates the parent section of a project so
that it references the newest
available version. For example, if
you use a corporate root POM, this
goal can be helpful if you need to
ensure you are using the latest
version of the corporate root POM.
versions:update-child-modules updates the parent section of the
child modules of a project so the
version matches the version of the
current project. For example, if you
have an aggregator pom that is also
the parent for the projects that it
aggregates and the children and
parent versions get out of sync, this
mojo can help fix the versions of the
child modules. (Note you may need to
invoke Maven with the -N option in
order to run this goal if your
project is broken so badly that it
cannot build because of the version
mis-match).
versions:lock-snapshots searches the pom for all -SNAPSHOT
versions and replaces them with the
current timestamp version of that
-SNAPSHOT, e.g. -20090327.172306-4
versions:unlock-snapshots searches the pom for all timestamp
locked snapshot versions and replaces
them with -SNAPSHOT.
versions:resolve-ranges finds dependencies using version ranges and
resolves the range to the specific
version being used.
versions:use-releases searches the pom for all -SNAPSHOT versions
which have been released and replaces
them with the corresponding release
version.
versions:use-next-releases searches the pom for all non-SNAPSHOT
versions which have been a newer
release and replaces them with the
next release version.
versions:use-next-versions searches the pom for all versions
which have been a newer version and
replaces them with the next version.
versions:commit removes the pom.xml.versionsBackup files. Forms
one half of the built-in "Poor Man's
SCM".
versions:revert restores the pom.xml files from the
pom.xml.versionsBackup files. Forms
one half of the built-in "Poor Man's
SCM".
Just thought I'd include it for any future reference.
Please take a look at this page (section "Dependency Version Ranges"). What you might want to do is something like
<version>[1.2.3,)</version>
These version ranges are implemented in Maven2.
Unlike others I think there are many reasons why you might always want the latest version. Particularly if you are doing continuous deployment (we sometimes have like 5 releases in a day) and don't want to do a multi-module project.
What I do is make Hudson/Jenkins do the following for every build:
mvn clean versions:use-latest-versions scm:checkin deploy -Dmessage="update versions" -DperformRelease=true
That is I use the versions plugin and scm plugin to update the dependencies and then check it in to source control. Yes I let my CI do SCM checkins (which you have to do anyway for the maven release plugin).
You'll want to setup the versions plugin to only update what you want:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>versions-maven-plugin</artifactId>
<version>1.2</version>
<configuration>
<includesList>com.snaphop</includesList>
<generateBackupPoms>false</generateBackupPoms>
<allowSnapshots>true</allowSnapshots>
</configuration>
</plugin>
I use the release plugin to do the release which takes care of -SNAPSHOT and validates that there is a release version of -SNAPSHOT (which is important).
If you do what I do you will get the latest version for all snapshot builds and the latest release version for release builds. Your builds will also be reproducible.
Update
I noticed some comments asking some specifics of this workflow. I will say we don't use this method anymore and the big reason why is the maven versions plugin is buggy and in general is inherently flawed.
It is flawed because to run the versions plugin to adjust versions all the existing versions need to exist for the pom to run correctly. That is the versions plugin cannot update to the latest version of anything if it can't find the version referenced in the pom. This is actually rather annoying as we often cleanup old versions for disk space reasons.
Really you need a separate tool from maven to adjust the versions (so you don't depend on the pom file to run correctly). I have written such a tool in the the lowly language that is Bash. The script will update the versions like the version plugin and check the pom back into source control. It also runs like 100x faster than the mvn versions plugin. Unfortunately it isn't written in a manner for public usage but if people are interested I could make it so and put it in a gist or github.
Going back to workflow as some comments asked about that this is what we do:
We have 20 or so projects in their own repositories with their own jenkins jobs
When we release the maven release plugin is used. The workflow of that is covered in the plugin's documentation. The maven release plugin sort of sucks (and I'm being kind) but it does work. One day we plan on replacing this method with something more optimal.
When one of the projects gets released jenkins then runs a special job we will call the update all versions job (how jenkins knows its a release is a complicated manner in part because the maven jenkins release plugin is pretty crappy as well).
The update all versions job knows about all the 20 projects. It is actually an aggregator pom to be specific with all the projects in the modules section in dependency order. Jenkins runs our magic groovy/bash foo that will pull all the projects update the versions to the latest and then checkin the poms (again done in dependency order based on the modules section).
For each project if the pom has changed (because of a version change in some dependency) it is checked in and then we immediately ping jenkins to run the corresponding job for that project (this is to preserve build dependency order otherwise you are at the mercy of the SCM Poll scheduler).
At this point I'm of the opinion it is a good thing to have the release and auto version a separate tool from your general build anyway.
Now you might think maven sort of sucks because of the problems listed above but this actually would be fairly difficult with a build tool that does not have a declarative easy to parse extendable syntax (aka XML).
In fact we add custom XML attributes through namespaces to help hint bash/groovy scripts (e.g. don't update this version).
The dependencies syntax is located at the Dependency Version Requirement Specification documentation. Here it is is for completeness:
Dependencies' version element define version requirements, used to compute effective dependency version. Version requirements have the following syntax:
1.0: "Soft" requirement on 1.0 (just a recommendation, if it matches all other ranges for the dependency)
[1.0]: "Hard" requirement on 1.0
(,1.0]: x <= 1.0
[1.2,1.3]: 1.2 <= x <= 1.3
[1.0,2.0): 1.0 <= x < 2.0
[1.5,): x >= 1.5
(,1.0],[1.2,): x <= 1.0 or x >= 1.2; multiple sets are comma-separated
(,1.1),(1.1,): this excludes 1.1 (for example if it is known not to
work in combination with this library)
In your case, you could do something like <version>[1.2.3,)</version>
Are you possibly depending on development versions that obviously change a lot during development?
Instead of incrementing the version of development releases, you could just use a snapshot version that you overwrite when necessary, which means you wouldn't have to change the version tag on every minor change. Something like 1.0-SNAPSHOT...
But maybe you are trying to achieve something else ;)
Who ever is using LATEST, please make sure you have -U otherwise the latest snapshot won't be pulled.
mvn -U dependency:copy -Dartifact=com.foo:my-foo:LATEST
// pull the latest snapshot for my-foo from all repositories
The truth is even in 3.x it still works, surprisingly the projects builds and deploys. But the LATEST/RELEASE keyword causing problems in m2e and eclipse all over the place, ALSO projects depends on the dependency which deployed through the LATEST/RELEASE fail to recognize the version.
It will also causing problem if you are try to define the version as property, and reference it else where.
So the conclusion is use the versions-maven-plugin if you can.
By the time this question was posed there were some kinks with version ranges in maven, but these have been resolved in newer versions of maven.
This article captures very well how version ranges work and best practices to better understand how maven understands versions: https://docs.oracle.com/middleware/1212/core/MAVEN/maven_version.htm#MAVEN8855
Sometimes you don't want to use version ranges, because it seems that they are "slow" to resolve your dependencies, especially when there is continuous delivery in place and there are tons of versions - mainly during heavy development.
One workaround would be to use the versions-maven-plugin. For example, you can declare a property:
<properties>
<myname.version>1.1.1</myname.version>
</properties>
and add the versions-maven-plugin to your pom file:
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>versions-maven-plugin</artifactId>
<version>2.3</version>
<configuration>
<properties>
<property>
<name>myname.version</name>
<dependencies>
<dependency>
<groupId>group-id</groupId>
<artifactId>artifact-id</artifactId>
<version>latest</version>
</dependency>
</dependencies>
</property>
</properties>
</configuration>
</plugin>
</plugins>
</build>
Then, in order to update the dependency, you have to execute the goals:
mvn versions:update-properties validate
If there is a version newer than 1.1.1, it will tell you:
[INFO] Updated ${myname.version} from 1.1.1 to 1.3.2
If you want Maven should use the latest version of a dependency, then you can use Versions Maven Plugin and how to use this plugin, Tim has already given a good answer, follow his answer.
But as a developer, I will not recommend this type of practices. WHY?
answer to why is already given by Pascal Thivent in the comment of the question
I really don't recommend this practice (nor using version ranges) for
the sake of build reproducibility. A build that starts to suddenly
fail for an unknown reason is way more annoying than updating manually
a version number.
I will recommend this type of practice:
<properties>
<spring.version>3.1.2.RELEASE</spring.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring.version}</version>
</dependency>
</dependencies>
it is easy to maintain and easy to debug. You can update your POM in no time.
MY solution in maven 3.5.4 ,use nexus, in eclipse:
<dependency>
<groupId>yilin.sheng</groupId>
<artifactId>webspherecore</artifactId>
<version>LATEST</version>
</dependency>
then in eclipse: atl + F5, and choose the force update of snapshots/release
it works for me.
I have a Maven project with 2 modules. I want the modules to inherit the version of that project, without defining it as a parent in the POM file of any submodules (the reason behind that is that the modules already have parents). What would be the best way to achieve that?
Importing the version from a properties file doesn't work because maven expects a constant value as a project version, not an expression. Maven plugins such as the version maven plugin or the maven release plugin are not solutions to my problem because I need something that would work in an IDE (I have to use Eclipse for packaging the projects, not my call).
Edit
To clarify things (apologies if my original post was not clear enough)
Main Project POM file
...
<groupId>org.mygroup</groupId>
<artifactId>parentproject</artifactId>
<version>1.1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>module1</module>
<module>module2</module>
</modules>
...
Module POM file example
...
<groupId>org.mygroup</groupId>
<artifactId>module1</artifactId>
<version>1.1.0-SNAPSHOT</version>
<packaging>war</packaging>
<parent>
<!-- Some parent that's NOT the main project, e.g. Spring Boot -->
</parent>
...
What I want is a solution that would allow me to set the version only ONCE (e.g. in the main project POM file) and having every module of that project to "inherit" that version.
You should probably set the parent back to your actual parent project. Version numbers between modules can be simultanuously updated using mvn versions:set. If you need the version number for cross-module dependencies, use ${project.version}. If you want to embed another Maven configuration file for its dependencies, consider using a Bill-of-material (BOM): https://stackoverflow.com/a/14876651 . Hope things brings you to your answer!
I really can't think of any Maven facility that fit 100% your necessities. Event if you could set the parentproject as an actual parent on each submodule, you'd need to specify its version in the parent declaration, so...
But I think of a trick to do the job through an authomatism, so that every time the parent version is changed, it will be automatically propagated to each submodule. It can be done like this:
Program a plugin in the parent project that writes the version id on each of its modules' pom files (for example, through an XSL transformation with the xml-maven-plugin).
Then, link this plugin to the package phase, so that every time the parent is build, the versions gets propagated to the submodules.
You only will have to refresh the submodules projects in Eclipse to make Eclipse be aware of the changes.
But if you don't want to refresh manually, there is still another alternative - fully based on Eclipse:
Make an Ant script to perform the copy-version-to-all-module-poms task. And, instead of calling it from a Maven phase, program an Eclipse builder to call it and, within this builder, program also a refresh of the specific modules. So, every time you execute a build of your project, it will copy its version to the submodules and make Eclipse be aware of this change.
I have a Maven project, which uses JAR packaging. When I run the install phase, it will install both Project-1.0.jar and Project-1.0.pom files in my local repository.
Now I would like the JAR to be built with a classifier. This is easy enough: I just add the line to my jar plugin configuration:
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<classifier>whatever</classifier>
[...]
</configuration>
</plugin>
Now, this works in that it installs Project-1.0-whatever.jar in my repo, but no longer installs a POM.
In case it matters, I want to use this feature in conjunction with profiles, i.e. I want to build JARs with different classifiers with different profiles.
The reason I want the POM is because I have other projects depending on this one. When I build one of these, it will try to find a POM for this dependency. If it can't, it will happily use the JAR, but that is not an acceptable solution for me for a couple of reasons:
It's bad enough that it will try to contact external repos and look for it, but even worse, we use a share repo, so it will download the POM from the shared repo, which may not be what I want - for example if I just made changes to the POM and am trying to test them.
Is there a solution, or can anyone suggest a reasonable workaround?
EDIT: I just discovered that the issue affects Maven 2.2.1, but not Maven 3.0.5. This may therefore be a bug or a difference in features between versions. I would still be interested in solutions/workarounds for Maven 2, as migrating the project to Maven 3 is a complicated affair and not likely to happen.
The reason turned out to be nothing to do with Maven version as such, and everything to do with the version of maven-install-plugin. It turns out versions prior to 2.3 have this bug.
Old installations of Maven are somewhat likely to suffer this issue, as Maven 2 will use any version of a plugin that it has unless a version has been explicitly specified in the POM, but maven-install-plugin is included by default and it's quite possible for a POM not to explicitly specify it at all (as it was in my case).
Recently I wrote a project with maven, but I have a question about the version in maven pom.xml.
If I write such a dependency
<dependency>
<groupId>foo</groupId>
<artifactId>bar</artifactId>
<!--No version here-->
</dependency>
what will the version be
in a simple project, no subproject
as a dependency in another project and that project use foo-bar-1.0.0
Part 1. of your question: If you don't specify a version there are various different outcomes:
a) you will get an error...
[ERROR] The project org.example:myproject:0.5-SNAPSHOT (D:\src\myproject\pom.xml) has 1 error
[ERROR] 'dependencies.dependency.version' for foo:bar:jar is missing. # line 39, column 14
b) if you have defined the version in the dependency management of the project's parent's pom, then that version is taken. The parent of the project doesn't have to be an enclosing superproject. It can simply be a collection of appropriate definitions.
c) if another dependency of your project also depends on foo:bar, and specifies a version, then that version is taken. Maven 2 has a mechanism called transitive dependencies. If the version of a dependency is not explicitly specified for an artifact, it searches the dependency tree and uses the nearest definition in the tree. If there are two nearest definitions, then the first declaration wins (since maven 2.0.9).
Part 2.: I am not sure, but maybe the transitive dependency mechanism also works that way. But the documentation (as far as I understood it) doesn't mention that case.
But somehow I feel that the second part of your question doesn't make sense: I guess that in order to use an artifact as a dependency, you would have to build it first. So you'd have to know the version of the dependencies well before it is used as a dependency itself.