What exactly is a Maven Snapshot and why do we need it

Question

I am a bit confused about the meaning of a Maven Snapshot and why we build one

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A  release  is the final build for a version which does not change   A  snapshot  is a build which can be replaced by another build which has the same name   It implies that the build could change at any time and is still under active development   You have different artifacts for different builds based on the same code  E g  you might have one with debugging and one without  One for Java 5 0 and one for Java 6   Generally its simpler to have one build which does everything you need

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The  SNAPSHOT  term means that the build is a snapshot of your code at a given time   It usually means that this version is still under heavy development   When the code is ready and it is time to release it  you will want to change the version listed in the POM  Then instead of having a  SNAPSHOT  you would use a label like  1 0    For some help with versioning  check out the Semantic Versioning specification

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A Maven SNAPSHOT is an artifact created by a Maven build and pretends to help developers in the software  development cycle  A SNAPSHOT is an artifact  or project build result   that is not pretended to be used anywhere  it s only a temporarily  jar   ear      created to test the build process or to test new requirements that are not yet ready to go to a production environment  After you are happy with the SNAPSHOT artifact quality  you can create a RELEASE artifact that can be used by other projects or can be deployed itself  In your project  you can define a SNAPSHOT using the version element in the pom xml file of Maven   lt groupId gt example project maven lt  groupId gt   lt artifactId gt MavenEclipseExample lt  artifactId gt   lt version gt 0 0 1-SNAPSHOT lt  version gt   lt packaging gt jar lt  packaging gt   lt description gt Maven pom example lt  description gt   If you want to understand better Maven you can look into these articles too  https   connected2know com programming menu-maven-articles

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This is how a snapshot looks like for a repository and in this case is not enabled  which means that the repository referred in here is stable and there s no need for updates    lt project gt               lt repositories gt           lt repository gt               lt id gt lds-main lt  id gt               lt name gt LDS Main Repo lt  name gt               lt url gt http   code lds org nexus content groups main-repo lt  url gt               lt snapshots gt                   lt enabled gt false lt  enabled gt               lt  snapshots gt           lt  repository gt       lt  repositories gt   lt  project gt    Another case would be for    lt snapshots gt           lt enabled gt true lt  enabled gt   lt  snapshots gt    which means that Maven will look for updates for this repository  You can also specify an interval for the updates with  tag

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As the name suggests  snapshot refers to a state of project and its dependencies at that moment of time  Whenever maven finds a newer SNAPSHOT of the project  it downloads and replaces the older  jar file of the project in the local repository   Snapshot versions are used for projects under active development  If your project depends on a software component that is under active development  you can depend on a snapshot release  and Maven will periodically attempt to download the latest snapshot from a repository when you run a build

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understanding the context of SDLC will help understand the difference between snapshot and the release  During the dev process developers all contribute their features to a baseline branch  At some point the lead thinks enough features have accumulated then he will cut a release branch from the baseline branch  Any builds prior to this time point are snapshots  Builds post to this point are releases  Be noted  release builds could change too before going to production if any defect spot during the release testing

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A snapshot version in Maven is one that has not been released   The idea is that before a 1 0 release  or any other release  is done  there exists a 1 0-SNAPSHOT  That version is what might become 1 0  It s basically  1 0 under development   This might be close to a real 1 0 release  or pretty far  right after the 0 9 release  for example    The difference between a  real  version and a snapshot version is that snapshots might get updates  That means that downloading 1 0-SNAPSHOT today might give a different file than downloading it yesterday or tomorrow   Usually  snapshot dependencies should only exist during development and no released version  i e  no non-snapshot  should have a dependency on a snapshot version

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I d like to make a point about terminology  The other answers gave good explanations about what a  snapshot  version is in the context of Maven  But does it follow that a non-snapshot version should be termed a  release  version   There is some tension between the semantic versioning idea of a  release  version  which would seem to be any version that does not have a qualifier such as -SNAPSHOT but also does not have a qualifier such as -beta 4  and Maven s idea idea of a  release  version  which only seems to include the absence of -SNAPSHOT   In other words  there is a semantic ambiguity of whether  release  means  we can release it to Maven Central  or  the software is in its final release to the public   We could consider -beta 4 to be a  release  version if we release it to the public  but it s not a  final release   Semantic versioning clearly says that something like -beta 4 is a  pre-release  version  so it wouldn t make sense for it to be called a  release  version  even without -SNAPSHOT  In fact by definition even -rc 5 is a release candidate  not an actual release  even though we may allow public access for testing   So Maven notwithstanding  in my opinion it seems more appropriate only to call a  release  version one that doesn t have any qualifier at all  not even -beta 4  Perhaps a better name for a Maven non-snapshot version would be a  stable  version  inspired by another answer   Thus we would have    1 2 3-beta 4-SNAPSHOT  A snapshot version of a pre-release version  1 2 3-SNAPSHOT  A snapshot version of a release version  1 2 3-beta 4  A stable version of a pre-release version  1 2 3  A release version  which is a stable  non-snapshot version  obviously

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Snapshot simply means depending on your configuration Maven will check latest changes on a special dependency  Snapshot is unstable because it is under development but if on a special project needs to has a latest changes you must configure your dependency version to snapshot version  This scenario occurs in big organizations with multiple products that these products related to each other very closely

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Maven versions can contain a string literal  SNAPSHOT  to signify that a project is currently under active development   For example  if your project has a version of    1 0-SNAPSHOT    and you deploy this project   s artifacts to a Maven repository  Maven would expand this version to    1 0-20080207-230803-1    if you were to deploy a release at 11 08 PM on February 7th  2008 UTC  In other words  when you deploy a snapshot  you are not making a release of a software component  you are releasing a snapshot of a component at a specific time   So mainly snapshot versions are used for projects under active development  If your project depends on a software component that is under active development  you can depend on a snapshot release  and Maven will periodically attempt to download the latest snapshot from a repository when you run a build  Similarly  if the next release of your system is going to have a version    1 8     your project would have a    1 8-SNAPSHOT    version until it was formally released   For example   the following dependency would always download the latest 1 8 development JAR of spring        lt dependency gt           lt groupId gt org springframework lt  groupId gt           lt artifactId gt spring lt  artifactId gt           lt version gt 1 8-SNAPSHOT    lt  version gt       lt  dependency gt    Maven  An example of maven release process

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usually in maven we have two types of builds  1 Snapshot builds 2 Release builds   snapshot builds SNAPSHOT is the special version that indicate current deployment copy not like a regular version  maven checks the version for every build in the remote repository so the snapshot builds are nothing but development builds  Release builds Release means removing the SNAPSHOT at the version for the build  these are the regular build versions

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simply snapshot means it is the version which is not stable one   when version includes snapshot like 1 0 0 -SNAPSHOT means it is not stable version and look for remote repository to resolve dependencies

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Snapshot Dependencies Snapshot dependencies are dependencies  JAR files  which are under development  Instead of constantly updating the version numbers to get the latest version  you can depend on a snapshot version of the project  Snapshot versions are always downloaded into your local repository for every build  even if a matching snapshot version is already located in your local repository  Always downloading the snapshot dependencies assures that you always have the latest version in your local repository  for every build  your pom contains a lot of -SNAPSHOT dependencies and those -SNAPSHOT dependencies are a moving target   https   dzone com articles maven-release-plugin-in-the-enterprise https   javarevisited blogspot com 2019 03 top-5-course-to-learn-apache-maven-for html https   www mojohaus org versions-maven-plugin examples lock-snapshots html http   tutorials jenkov com maven maven-tutorial html

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The three others answers provide you a good vision of what a -SNAPSHOT version is  I just wanted to add some information regarding the behavior of Maven when it finds a SNAPSHOT dependency   When you build an application  Maven will search for dependencies in the local repository  If a stable version is not found there  it will search the remote repositories  defined in settings xml or pom xml  to retrieve this dependency  Then  it will copy it into the local repository  to make it available for the next builds   For example  a foo-1 0 jar library is considered as a stable version  and if Maven finds it in the local repository  it will use this one for the current build   Now  if you need a foo-1 0-SNAPSHOT jar library  Maven will know that this version is not stable and is subject to changes  That s why Maven will try to find a newer version in the remote repositories  even if a version of this library is found on the local repository  However  this check is made only once per day  That means that if you have a foo-1 0-20110506 110000-1 jar  i e  this library has been generated on 2011 05 06 at 11 00 00  in your local repository  and if you run the Maven build again the same day  Maven will not check the repositories for a newer version   Maven provides you a way to change this update policy in your repository definition    lt repository gt       lt id gt foo-repository lt  id gt       lt url gt     lt  url gt       lt snapshots gt           lt enabled gt true lt  enabled gt           lt updatePolicy gt XXX lt  updatePolicy gt       lt  snapshots gt   lt  repository gt    where XXX can be    always  Maven will check for a newer version on every build  daily  the default value  interval XXX  an interval in minutes  XXX  never  Maven will never try to retrieve another version  It will do that only if it doesn t exist locally  With the configuration  SNAPSHOT version will be handled as the stable libraries     model of the settings xml can be found here

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