Maven install error: Dependency could not be resolved - maven

Question

I am using Maven 3.1.1. When I run mvn install I get the following error:
D:\spring source>mvn install
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building SpringDependencies 1.0
[INFO] ------------------------------------------------------------------------
Downloading: http://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-
dependency-plugin/2.8/maven-dependency-plugin-2.8.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.648s
[INFO] Finished at: Mon Dec 16 15:01:47 IST 2013
[INFO] Final Memory: 4M/15M
[INFO] ------------------------------------------------------------------------
[ERROR] Plugin org.apache.maven.plugins:maven-dependency-plugin:2.8 or one of it
s dependencies could not be resolved: Failed to read artifact descriptor for org
.apache.maven.plugins:maven-dependency-plugin:jar:2.8: Could not transfer artifa
ct org.apache.maven.plugins:maven-dependency-plugin:pom:2.8 from/to central (htt
p://repo.maven.apache.org/maven2): repo.maven.apache.org: Unknown host repo.mave
n.apache.org -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e swit
ch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please rea
d the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginResoluti
onException
My pom.xml is:
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>spring-source-download</groupId>
<artifactId>SpringDependencies</artifactId>
<version>1.0</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>4.0.0.RELEASE</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>3.1.1</version>
<executions>
<execution>
<id>download-dependencies</id>
<phase>generate-resources</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory> ${project.build.directory}/dependencies </outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

Answer 1

Could not transfer artifact
org.apache.maven.plugins:maven-dependency-plugin:pom:2.8 from/to
central (http://repo.maven.apache.org/maven2): repo.maven.apache.org:
Unknown host repo.maven.apache.org
It seems like your maven cannot access remote central repository.
Check if you have an established internet connection.
Check if you can access default maven repo http://repo.maven.apache.org/maven2 in your browser.
Check if you have correct configuration in <repositories> and <proxies> in your your settings.xml

Answer 2

This error comes due to the proxy settings.
First of all, check whether you are able to connect to maven repository(http://repo1.maven.org/maven2) from browser.
Then update Maven proxy setting create/update a settings.xml in .m2 directory with following details:
<proxies>
<proxy>
<active>true</active>
<protocol>http</protocol>
<host>{your proxy server host name}</host>
<port>{your proxy server port}</port>
<nonProxyHosts>maven</nonProxyHosts>
</proxy>
</proxies>
Solution given by Maven community: http://maven.apache.org/guides/mini/guide-proxies.html

Answer 3

This is caused by corrupted maven or plugins folder. To resolve this:
Delete \.m2\repository\org\apache\maven
mvn dependency:resolve -X

Answer 4

Where is my Settings.xml?
Windows users
It's in your C:/Users/<Username>/.m2/settings.xml
Also, this is for specific user.
Global one can be present at :
<Maven-Installation-Directory>/conf/settings.xml
But changing the User one might solve the issue if you can't find the global one.
Also, equally important, go to Preferences in Eclipse/STS:
Goto Maven -> User Settings
and verify if both global and user settings.xml files are mentioned in the properties, if not mention them by browsing.
1. Proxy Issue
Check Windows Proxy Setting.
If there is any proxy which your computer is using then you need to add proxy settings in your settings.xml file too.
Just add this chunk of code in your settings.xml
<proxies>
<proxy>
<id>proxy-id</id>
<active>true</active>
<protocol>http</protocol>
<host>ca-something.net</host>
<port>80</port>
<nonProxyHosts>localhost|10.140.240.90.*</nonProxyHosts>
</proxy>
</proxies>
2. Protocol Issue
Visit http://repo.maven.apache.org/: If it says Https required.
Then, you need to add this chunk of code to your settings.xml inside <mirrors>
<mirror>
<id>central-secure</id>
<url>https://repo.maven.apache.org/maven2</url>
<mirrorOf>central</mirrorOf>
</mirror>
Now it should be good to go.
3. None of the above works
Try disconnecting any company private VPN and try mvn clean build.

Answer 5

Disconnect from VPN and then run the command.

Answer 6

Probably a bit late to the party, but there appears to be an unknown host exception thrown out of maven even if the resource/dependency is unavailable at that address.
Which could mean that the problem may actually be that you have a transitive dependency that is pointing you to the wrong version of a jar (or one that is transitively included multiple times - one of which may be an unresolvable version). (I see it's looking for version 2.8 of the plugin but you specified version 3.1.1, so it's likely you have another dependency transitively including the wrong version).
You can exclude transitive inclusion of a dependency using the exclusions tag.

Answer 7

This issue was resolved for us by providing the correct proxy host in .m2/settings.xml.
Example:
<proxies>
<proxy>
<id>XXXXXXXXXX</id>
<active>true</active>
<protocol>http</protocol>
<host>na-xxxx-proxy.na.xxxxxxxxxx.net</host>
<port>80</port>
<nonProxyHosts>localhost|10.140.240.90.*</nonProxyHosts>
</proxy>
</proxies>