Why is Maven downloading the maven-metadata xml every time

Question

Below is the error I usually get when my internet connection is flanky when trying to build a web application with maven    My question is that  why does maven always have to download every time when the same app has been built earlier    What could be wrong in my configuration that makes maven to download every time    Below is an error I get when I try to build offline     INFO  ------------------------------------------------------------------------  INFO  Building mywebapp 1 0-SNAPSHOT  INFO  ------------------------------------------------------------------------ Downloading  https   raw github com pagecrumb mungo mvn-repo com pagecrumb mungo 0 0 1-SNAPSHOT maven-metadata xml   WARNING  Could not transfer metadata com mywebapp mungo 0 0 1-SNAPSHOT maven-metadata xml  from to mungo-mvn-repo  https   raw github com pagecrumb mungo mvn-repo    raw github com  INFO    INFO  --- maven-war-plugin 2 1 1 war  default-cli    mywebapp ---  INFO  Packaging webapp  INFO  Assembling webapp  mywebapp  in  D  workspace web target mywebapp-1 0-SNAPSHOT   INFO  Processing war project  INFO  Copying webapp resources  D  workspace web src main webapp   INFO  Webapp assembled in  1237 msecs   INFO  Building war  D  workspace web target mywebapp-1 0-SNAPSHOT war  WARNING  Warning  selected war files include a WEB-INF web xml which will be ignored   webxml attribute is missing from war task   or ignoreWebxml attribute is specified as  true    INFO                                                                            INFO  ------------------------------------------------------------------------  INFO  Building com mywebapp  com mywebapp  0 0 1-SNAPSHOT  INFO  ------------------------------------------------------------------------ Downloading  http   repo maven apache org maven2 org apache maven plugins maven-release-plugin 2 1 maven-release-plugin-2 1 pom   WARNING  Failed to retrieve plugin descriptor for org apache maven plugins maven-release-plugin 2 1  Plugin org apache maven plugins maven-release-plugin 2 1 or one of its dependencies could not be resolved  Failed to read artifact descriptor for org apache maven plugins maven-release-plugin jar 2 1 Downloading  http   download java net maven 2 org apache maven plugins maven-metadata xml Downloading  http   download java net maven 2 org codehaus mojo maven-metadata xml  397 397 B     Downloaded  http   download java net maven 2 org codehaus mojo maven-metadata xml  397 B at 0 0 KB sec   WARNING  Failure to transfer org apache maven plugins maven-war-plugin maven-metadata xml from http   download java net maven 2 was cached in the local repository  resolution will not be reattempted until the update interval of maven2-repository dev java net has elapsed or updates are forced  Original error  Could not transfer metadata org apache maven plugins maven-war-plugin maven-metadata xml from to maven2-repository dev java net  http   download java net maven 2   download java net  INFO    INFO  --- maven-war-plugin 2 3 war  default-cli    mywebapp-build ---  INFO  Packaging webapp  INFO  Assembling webapp  mywebapp-build  in  D  workspace target mywebapp-build-0 0 1-SNAPSHOT   INFO  Processing war project  INFO  Webapp assembled in  15 msecs   INFO  Building war  D  workspace target mywebapp-build-0 0 1-SNAPSHOT war  INFO  ------------------------------------------------------------------------  INFO  Reactor Summary   INFO    INFO  mywebapp                                       SUCCESS  27 999s   INFO  com mywebapp  com mywebapp                        FAILURE  1 00 406s   INFO  ------------------------------------------------------------------------  INFO  BUILD FAILURE  INFO  ------------------------------------------------------------------------  INFO  Total time  1 41 409s  INFO  Finished at  Tue May 07 22 13 38 SGT 2013  INFO  Final Memory  11M 28M  INFO  ------------------------------------------------------------------------  ERROR  Failed to execute goal org apache maven plugins maven-war-plugin 2 3 war   default-cli  on project mywebapp-build  Error assembling WAR  webxml attribute is required  or pre-existing WEB-INF web xml if executing in update mode

User · Answer

Maven does this because your dependency is in a SNAPSHOT version and maven has no way to detect any changes made to that snapshot version in the repository  Release your artifact and change the version in pom xml to that version and maven will no longer fetch the metadata file

User · Answer

Look in your settings xml  or  possibly your project s parent or corporate parent POM  for the  lt repositories gt  element   It will look something like the below    lt repositories gt       lt repository gt           lt id gt central lt  id gt           lt url gt http   gotoNexus lt  url gt           lt snapshots gt               lt enabled gt true lt  enabled gt               lt updatePolicy gt always lt  updatePolicy gt           lt  snapshots gt           lt releases gt               lt enabled gt true lt  enabled gt               lt updatePolicy gt daily lt  updatePolicy gt           lt  releases gt       lt  repository gt   lt  repositories gt    Note the  lt updatePolicy gt  element   The example tells Maven to contact the remote repo  Nexus in my case  Maven Central if you re not using your own remote repo  any time Maven needs to retrieve a snapshot artifact during a build  checking to see if there s a newer copy   The metadata is required for this   If there is a newer copy Maven downloads it to your local repo   In the example  for releases  the policy is daily so it will check during your first build of the day   never is also a valid option  as described in Maven settings docs   Plugins are resolved separately   You may have repositories configured for those as well  with different update policies if desired    lt pluginRepositories gt       lt pluginRepository gt           lt id gt central lt  id gt           lt url gt http   gotoNexus lt  url gt           lt snapshots gt               lt enabled gt true lt  enabled gt               lt updatePolicy gt daily lt  updatePolicy gt           lt  snapshots gt           lt releases gt               lt enabled gt true lt  enabled gt               lt updatePolicy gt never lt  updatePolicy gt           lt  releases gt       lt  pluginRepository gt   lt  pluginRepositories gt    Someone else mentioned the -o option   If you use that  Maven runs in  offline  mode  It knows it has a local repo only  and it won t contact the remote repo to refresh the artifacts no matter what update policies you use

User · Answer

It is possibly to use the flag -o --offline  Work offline  to prevent that   Like this   maven compile -o

User · Answer

I suppose because you didn t specify plugin version so it triggers the download of associated metadata in order to get the last one   Otherwise did you try to force local repo usage using -o

User · Answer

I haven t studied yet  when Maven does which look-up  but to get stable and reproducible builds  I strongly recommend not to access Maven Respositories directly but to use a Maven Repository Manager such as Nexus   Here is the tutorial how to set up your settings file   http   books sonatype com nexus-book reference maven-sect-single-group html  http   maven apache org repository-management html

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