Maven/Ivy: Identical artifact with different name in dependency

Maven/Ivy: Identical artifact with different name in dependency - maven-2

Currently I am using Ivy for dependency management. And quite often I come across problem of getting identical jar files with different name due to transitive dependency.
Example:
<dependency>
<groupId>javax.mail</groupId>
<artifactId>mail</artifactId>
<version>1.4</version>
</dependency>
<dependency>
<groupId>org.apache.geronimo.specs</groupId>
<artifactId>geronimo-javamail_1.4_spec</artifactId>
<version>1.4</version>
</dependency>
I am thinking of trying out Maven as well.
Any best practice to eliminate these identical artifact in either Ivy or Maven?

Global exclusion of artifacts would be a nice feature to deal with this kind of situation - same artifact with different names - until Maven provides a better way to deal with "Specs JARs" aka Virtual Dependencies.
Unfortunately, such a feature is currently not available (see MNG-3196 and MNG-1977) so you will have to declare dependency exclusions to exclude the unwanted artifact from the dependency pulling it transitively. In Maven, this is done by adding an <exclusions> tag under the <dependency> section of the pom.
<project>
...
<dependencies>
<dependency>
<groupId>sample.ProjectA</groupId>
<artifactId>Project-A</artifactId>
<version>1.0</version>
<scope>compile</scope>
<exclusions>
<exclusion> <!-- declare the exclusion here -->
<groupId>sample.ProjectB</groupId>
<artifactId>Project-B</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
</project>
If Project-A-1.0.jar is used by all projects, one possible solution would be to declare this under the dependencyManagement section of a corporate POM to not repeat yourself.

In this particular example i would select the the javax one. And if you have artifacts which are coming under different names you can use excludes in Maven. I don't know if this is possible in Ivy.

Related

Why does Maven use already non-existent classes and dependencies from history in build

I am using maven 3.2.1. for my project.
Maven builds artifacts and puts classes and dependencies into them which do not exist. For example, I used omnifaces as dependency in pom-file. I removed omnifaces from pom-file weeks ago but maven still builds it into the artifact. Another issue is, that maven builds an old and the new structure of the project. I removed a package and put all the classes into another package but maven still builds the old package next to the new one. That causes a ClassCastException at some points.
I'd like to know if anyone knows about that problem. Is there a way to configure maven to use only the current dependecies and project structure to build artifacts?
<?xml version="1.0" encoding="UTF-8"?>
http://maven.apache.org/xsd/maven-4.0.0.xsd">
4.0.0
<parent>
<groupId>myProject</groupId>
<artifactId>webApplication</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>webApplication-war</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>myProject</groupId>
<artifactId>model-jar</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>myProject</groupId>
<artifactId>ordering-ejb</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>1.2</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<scope>provided</scope>
<version>2.5</version>
</dependency>
<dependency>
<groupId>javax.faces</groupId>
<artifactId>javax.faces-api</artifactId>
<version>2.2</version>
</dependency>
<dependency>
<groupId>javax.enterprise</groupId>
<artifactId>cdi-api</artifactId>
<version>1.2</version>
</dependency>
<dependency>
<groupId>org.primefaces</groupId>
<artifactId>primefaces</artifactId>
<version>5.0</version>
</dependency>
<dependency>
<groupId>javax.persistence</groupId>
<artifactId>persistence-api</artifactId>
<version>1.0.2</version>
<scope>provided</scope>
</dependency>
</dependencies>
<name>${project.artifactId}-1.0-SNAPSHOT</name>
<!--<url>http://localhost</url> -->
<!--<build>-->
<!--<finalName>${project.artifactId}-1.0-SNAPSHOT</finalName>-->
<!--<pluginManagement>-->
<!--<plugins>-->
<!--<plugin>-->
<!--<groupId>org.apache.maven.plugins</groupId>-->
<!--<artifactId>maven-war-plugin</artifactId>-->
<!--<version>2.4</version>-->
<!--<configuration>-->
<!--<packagingExcludes>WEB-INF/lib/model-1.0-SNAPSHOT.jar</packagingExcludes>-->
<!--<webappDirectory>src/main/webapp</webappDirectory>-->
<!--<webXml>src/main/webapp/WEB-INF/web.xml</webXml>-->
<!--<outputDirectory>${env.M3_REPO}/ordentity/webApplication/1.0-SNAPSHOT</outputDirectory>-->
<!--</configuration>-->
<!--</plugin>-->
<!--</plugins>-->
<!--</pluginManagement>-->
<!--<plugins>-->
<!--<plugin>-->
<!--<groupId>org.apache.maven.plugins</groupId>-->
<!--<artifactId>maven-dependency-plugin</artifactId>-->
<!--<version>2.8</version>-->
<!--<executions>-->
<!--<execution>-->
<!--<phase>install</phase>-->
<!--<goals>-->
<!--<goal>copy</goal>-->
<!--</goals>-->
<!--<configuration>-->
<!--<overWriteIfNewer>true</overWriteIfNewer>-->
<!--<artifactItems>-->
<!--<artifactItem>-->
<!--<groupId>${project.groupId}</groupId>-->
<!--<artifactId>${project.artifactId}</artifactId>-->
<!--<version>${project.version}</version>-->
<!--<type>${project.packaging}</type>-->
<!--</artifactItem>-->
<!--</artifactItems>-->
<!--<outputDirectory>${env.JBOSS_HOME}/standalone/deployments</outputDirectory>-->
<!--</configuration>-->
<!--</execution>-->
<!--</executions>-->
<!--</plugin>-->
<!--</plugins>-->
<!--</build>-->
Maven puts classes and directories into that war file which do not exist in project structure. I had a package called bean, but deleted it weeks ago. It still appears in the war file. I am really disapointed...
SOLVED: I found a helpful thread (link below) where a comment gave me the solution.
I found a classes directory in my project under:
webApplication/war/src/main/webapp/WEB-INF
It contained all the old classes which were build into the artifact as well. Therefore maven also built all the dependencies into the artifact. After I deleted the classes directory all the ugly sideeffects disappeared.
Why might Maven ignore updated classes during install?

SLF4J: Class path contains multiple SLF4J bindings

I'm getting the following error. It seems there are multiple logging frameworks bound to slf4j. Not sure how to resolve this. Any help is greatly appreciated.
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/Users/admin/.m2/repository/org/slf4j/slf4j-log4j12/1.6.4/slf4j-log4j12-1.6.4.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/Users/admin/.m2/repository/org/slf4j/slf4j-log4j12/1.6.1/slf4j-log4j12-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

Resolved by adding the following exclusion in the dependencies (of pom.xml) that caused conflict.
<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
</exclusions>

Gradle version;
configurations.all {
exclude module: 'slf4j-log4j12'
}

The error probably gives more information like this (although your jar names could be different)
SLF4J: Found binding in
[jar:file:/D:/Java/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in
[jar:file:/D:/Java/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.8.2/log4j-slf4j-impl-2.8.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
Noticed that the conflict comes from two jars, named logback-classic-1.2.3 and log4j-slf4j-impl-2.8.2.jar.
Run mvn dependency:tree in this project pom.xml parent folder, giving:
Now choose the one you want to ignore (could consume a delicate endeavor I need more help on this)
I decided not to use the one imported from spring-boot-starter-data-jpa (the top dependency) through spring-boot-starter and through spring-boot-starter-logging, pom becomes:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
in above pom spring-boot-starter-data-jpa would use the spring-boot-starter configured in the same file, which excludes logging (it contains logback)

Sbt version:
Append exclude("org.slf4j", "slf4j-log4j12") to the dependency that transitively includes slf4j-log4j12. For example, when using Spark with Log4j 2.6:
libraryDependencies ++= Seq(
// One SLF4J implementation (log4j-slf4j-impl) is here:
"org.apache.logging.log4j" % "log4j-api" % "2.6.1",
"org.apache.logging.log4j" % "log4j-core" % "2.6.1",
"org.apache.logging.log4j" % "log4j-slf4j-impl" % "2.6.1",
// The other implementation (slf4j-log4j12) would be transitively
// included by Spark. Prevent that with exclude().
"org.apache.spark" %% "spark-core" % "1.5.1" exclude("org.slf4j", "slf4j-log4j12")
)

1.Finding the conflicting jar
If it's not possible to identify the dependency from the warning, then you can use the following command to identify the conflicting jar
mvn dependency: tree
This will display the dependency tree for the project and dependencies who have pulled in another binding with the slf4j-log4j12 JAR.
Resolution
Now that we know the offending dependency, all that we need to do is exclude the slf4j-log4j12 JAR from that dependency.
Ex - if spring-security dependency has also pulled in another binding with the slf4j-log4j12 JAR, Then we need to exclude the slf4j-log4j12 JAR from the spring-security dependency.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
Note - In some cases multiple dependencies have pulled in binding with the slf4j-log4j12 JAR and you don't need to add exclude for each and every dependency that has pulled in.
You just have to do that add exclude dependency with the dependency which has been placed at first.
Ex -
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
</dependencies>
If you work with gradle then add following code to your build.gradle file to exclude SLF4J binding from all the modules
configurations.all {
exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
}

I just ignored/removed that jar file.

<!--<dependency>-->
<!--<groupId>org.springframework.boot</groupId>-->
<!--<artifactId>spring-boot-starter-log4j2</artifactId>-->
<!--</dependency>-->
I solved by delete this:spring-boot-starter-log4j2

Just use only required dependency, not all :))). For me, for normal work of logging process you need this dependency exclude others from pom.xml
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.5</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.1.8</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.1.8</version>
</dependency>

This is issue because of StaticLoggerBinder.class class belongs to two different jars. this class references from logback-classic-1.2.3.jar and same class also referenced from log4j-slf4j-impl-2.10.0.jar. both of jar in classpath. Hence there is conflict between them.
This is reason of log file is not generation even though log4j2.xml file in classpath [src/main/resource].
We have so select one of jar, I recommend use log4j-slf4j-impl-2.10.0.jar file and exclude logback-classic-1.2.3.jar file.
Solution: open pom file and view the dependency Hierarchy [eclipse] or run
mvn dependency:tree command to find out the dependency tree and source of dependency that download the dependency. find the conflicting dependency and exclude them. For Springboot application try this.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
This is working fine for me after struggling a lots.

...
org.codehaus.mojo
cobertura-maven-plugin
2.7
test
ch.qos.logback
logback-classic
tools
com.sun
...
## I fixed with this
...
org.codehaus.mojo
cobertura-maven-plugin
2.7
test
ch.qos.logback
logback-classic
tools
com.sun
...

For me, it turned out to be an Eclipse/Maven issue after switch from log4j to logback. Take a look into your .classpath file and search for the string "log4j".
In my case I had the following there:
<classpathentry kind="var" path="M2_REPO/org/slf4j/slf4j-log4j12/1.7.1/slf4j-log4j12-1.7.1.jar"/>
<classpathentry kind="var" path="M2_REPO/log4j/log4j/1.2.17/log4j-1.2.17.jar" />
Removing those entries from the file (or you could regenerate it) fixed the issue.

For me the answer was to force a Maven rebuild. In Eclipse:
Right click on project-> Maven -> Disable Maven nature
Right click on project-> Spring Tools > Update Maven Dependencies
Right click on project-> Configure > Convert Maven Project

I solved this by going to Project Structure from my Intellij project.
I deleted the file named: Maven: org.apache.logging.log4j:log4j-to-slf4j-impl:2.14.1
This file is not shown in this picture. You may see two libraries mentioned as log4j-to-slf4j. Delete one and you are good to go.

For all those looking for the solution for spring-boot-type dependencies, the magic incantation for Gradle is this:
configurations.all {
exclude group: 'ch.qos.logback', module: 'logback-classic'
}
in your build.gradle at the top level (not inside the dependencies block).
All other solutions found in the interwebs (including the one here suggesting to exclude the slf4j module) did not work for me.
This is what I have in my build.gradle (snippet):
// Removes the annoying warning about the multiple SLF4J implementations:
// SLF4J: Class path contains multiple SLF4J bindings.
configurations.all {
exclude group: 'ch.qos.logback', module: 'logback-classic'
}
dependencies {
annotationProcessor "org.springframework.boot:spring-boot-configuration-processor"
implementation ('org.springframework.boot:spring-boot-starter-actuator')
implementation ('org.springframework.boot:spring-boot-starter-data-mongodb-reactive')
implementation ('org.springframework.boot:spring-boot-starter-webflux')
annotationProcessor "org.projectlombok:lombok:${lombokVersion}"
compileOnly "org.projectlombok:lombok:${lombokVersion}"
// Removes the annoying warning:
// warning: unknown enum constant When.MAYBE
// reason: class file for javax.annotation.meta.When not found
// See: https://stackoverflow.com/questions/29805622/could-not-find-or-load-main-class-org-gradle-wrapper-gradlewrappermain/31622432
implementation group: 'com.google.code.findbugs', name: 'jsr305', version: '3.0.2'
// other stuff...
YMMV

I had the same problem. In my pom.xml i had both
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.28</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.2.1.RELEASE</version>
</dependency>
When i deleted the spring-boot-starter-web dependency, problem was solved.

I got this issue in a non-maven project, two depended jar each contained a slf4j. I solved
by remove one depended jar, compile the project(which of course getting failure) then add the removed one back.

In case these logs are the result of this fix:
https://stackoverflow.com/a/9919375/2894819
When one of your libraries actually use it. And your application doesn't need SL4J just replace implementation to runtimeOnly.
// contains dependency to sl4j-api
implementation("com.github.doyaaaaaken:kotlin-csv-jvm:1.2.0")
// add this to remove both warnings
runtimeOnly("org.slf4j:slf4j-nop:1.7.36")
In that case when you run your app the actual dependency will be included once by the library and won't be included to the bundle of your application.jar itself.

In my case I had 2 sources of dependencies for log4 one in C:\Program Files\smcf.ear directory and the second from maven which caused the multiple binding for sl4j.
Deleting the smcf.ear directory solved the issue for me.

The combination of <scope>provided</scope> and <exclusions> didn't work for me.
I had to use this:
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<scope>system</scope>
<systemPath>${project.basedir}/empty.jar</systemPath>
</dependency>
Where empty.jar is a jar file with literally nothing in it.

Seems removing .m2 directory and :
mvn install -DskipTests -T 4 resolved this issue for me.

Add jar (dependency with scope system) in an Ear build

I work with Maven and I want to do a build with packaging ear, i want to add a dependency with scope system and also with specifing the systemPath of the jar like follow:
<dependency>
<groupId>group1</groupId>
<artifactId>group1</artifactId>
<version>1</version>
<scope>system</scope>
<systemPath>D:\Buildear\Jars\file.jar</systemPath>
</dependency>
But I don't found the jar in my generater ear!!!
Help please.

I work with Maven and I want to do a build with packaging ear, I want to add a dependency with scope system (...). But I don't found the jar in my generater ear!!!
Yes, that's just what you get when (ab)using a system scoped dependency which is supposed to be always available by definition. I wrote many times about this, for example in this previous answer that I'm quoting below:
I already wrote many, many,
really many times about this
here on SO and in 99% of the cases,
system scoped dependencies should be
avoided. And I'll repeat what the
Dependency Scopes mini guide says
one more time:
system: This dependency is required in some phase of your
project's lifecycle, but is
system-specific. Use of this scope
is discouraged: This is considered an
"advanced" kind of feature and should
only be used when you truly understand
all the ramifications of its use,
which can be extremely hard if not
actually impossible to quantify.
This scope by definition renders your
build non-portable. It may be
necessary in certain edge cases. The
system scope includes the
<systemPath> element which points to
the physical location of this
dependency on the local machine. It is
thus used to refer to some artifact
expected to be present on the given
local machine an not in a repository;
and whose path may vary
machine-to-machine. The systemPath
element can refer to environment
variables in its path: ${JAVA_HOME}
for instance.
So, instead of using the system
scope, either:
Add your libraries to your local repository via install:install-file.
This is a quick and dirty way to get
things working, it might be an option
if you're alone but it makes your
build non portable.
Install and run an "enterprise repository" like Nexus, Archiva, or
Artifactory and add your libraries via
deploy:deploy-file. This is the
ideal scenario.
Setup a file based repository as described in this previous answer
and put your libraries in there. This
is the best compromise if you
don't have a corporate repository but
need to work as a team and don't want
to sacrifice portability.
Please, stop using the system scope.

<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<artifactId>aaa</artifactId>
<groupId>aaa</groupId>
<version>1.0</version>
</parent>
<groupId>aaa</groupId>
<artifactId>aaa</artifactId>
<version></version>
<packaging>ear</packaging>
<name>aaa - Ear</name>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>aaa-ejb</artifactId>
<version>${project.version}</version>
<type>ejb</type>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>aaa-webapp</artifactId>
<version>${project.version}</version>
<type>war</type>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>jboss</groupId>
<artifactId>jboss-common</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>jboss</groupId>
<artifactId>jbosssx</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.transaction</groupId>
<artifactId>jta</artifactId>
<version>1.1</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<finalName>${aaa.name}-${project.version}</finalName>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-ear-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<generateApplicationXml>false</generateApplicationXml>
<defaultLibBundleDir>lib</defaultLibBundleDir>
<modules>
<ejbModule>
<groupId>${project.groupId}</groupId>
<artifactId>aaa-ejb</artifactId>
</ejbModule>
<jarModule>
<groupId>xml-apis</groupId>
<artifactId>xml-apis</artifactId>
<excluded>true</excluded>
</jarModule>
</modules>
</configuration>
</plugin>
</plugins>
</build>
<properties>
<aaa.name>aaa-batch</aaa.name>
</properties>
This creates an ear and copies the libraries into the lib folder in the ear.

Exclude all transitive dependencies of a single dependency

In Maven2, to exclude a single transitive dependency, I have to do something like this:
<dependency>
<groupId>sample.group</groupId>
<artifactId>sample-artifactB</artifactId>
<version>1</version>
<exclusions>
<exclusion>
<groupId>sample.group</groupId>
<artifactId>sample-artifactAB</artifactId>
</exclusion>
</exclusions>
</dependency>
The problem with this approach is that I have to do this for every transitive dependency contributed by sample-artifactB.
Is there a way to use some sort of wildcard to exclude all transitive dependencies at once instead of one-by-one?

What has worked for me (may be a newer feature of Maven) is merely doing wildcards in the exclusion element.
I have a multi-module project that contains an "app" module that is referenced in two WAR-packaged modules. One of those WAR-packaged modules really only needs the domain classes (and I haven't separated them out of the app module yet). I found this to work:
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>app</artifactId>
<version>${project.version}</version>
<exclusions>
<exclusion>
<groupId>*</groupId>
<artifactId>*</artifactId>
</exclusion>
</exclusions>
</dependency>
The wildcard on both groupId and artifactId exclude all dependencies that normally would propagate through to the module using this dependency.

For maven2 there isn't a way to do what you describe. For maven 3, there is. If you are using maven 3 please see another answer for this question
For maven 2 I'd recommend creating your own custom pom for the dependency that has your <exclusions>. For projects that need to use that dependency, set the dependency to your custom pom instead of the typical artifact. While that does not necessarily allow you exclude all transitive dependencies with a single <exclusion>, it does allow you only have to write your dependency once and all of your projects don't need to maintain unnecessary and long exclusion lists.

One thing I have found useful:
If you put the dependency with the exclusions in the dependencyManagement section of either the parent POM for your project, or in an importable dependency management POM, then you don't need to repeat the exclusion (or the version).
For example, if your parent POM has:
<dependencyManagement>
<dependencies>
...
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.2.1</version>
<exclusions>
<exclusion>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</exclusion>
</exclusions>
</dependency>
....
</dependencies>
</dependencyManagement>
Then the modules in your project can simply declare the dependency as:
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
</dependency>
The in the parent POM will specify both the version and the exclusions. I use this technique for nearly all of our projects and it eliminates a lot of repetition.

Three years ago I recommended using Version 99 Does Not Exist, but now I've figured out a better way, especially since Version 99 is offline:
In your project's parent POM, use maven-enforcer-plugin to fail the build if the unwanted dependency creeps into the build. This can be done using the plugin's banned dependencies rule:
<plugin>
<artifactId>maven-enforcer-plugin</artifactId>
<version>1.0.1</version>
<executions>
<execution>
<id>only-junit-dep-is-used</id>
<goals>
<goal>enforce</goal>
</goals>
<configuration>
<rules>
<bannedDependencies>
<excludes>
<exclude>junit:junit</exclude>
</excludes>
</bannedDependencies>
</rules>
</configuration>
</execution>
</executions>
</plugin>
Then when that alerts you about an unwanted dependency, exclude it in the parent POM's <dependencyManagement> section:
<dependency>
<groupId>org.springframework.batch</groupId>
<artifactId>spring-batch-test</artifactId>
<version>2.1.8.RELEASE</version>
<exclusions>
<exclusion>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</exclusion>
</exclusions>
</dependency>
This way the unwanted dependency won't show up accidentally (unlike just an <exclusion> which is easy to forget), it won't be available even during compile time (unlike provided scope), there are no bogus dependencies (unlike Version 99) and it'll work without a custom repository (unlike Version 99). This approach will even work based on the artifact's version, classifiers, scope or a whole groupId - see the documentation for details.

I use the following workaround : instead of trying to exclude the artifact in all appropriate dependencies, I draw the dependency as "provided" at top level.
For example, to avoid shipping xml-apis "whatever version" :
<dependency>
<groupId>xml-apis</groupId>
<artifactId>xml-apis</artifactId>
<version>[1.0,]</version>
<scope>provided</scope>
</dependency>

Currently, there's no way to exclude more than one transitive dependency at a time, but there is a feature request for this on the Maven JIRA site:
https://issues.apache.org/jira/browse/MNG-2315

if you need to exclude all transitive dependencies from a dependency artifact that you are going to include in an assembly, you can specify this in the descriptor for the assembly-plugin:
<assembly>
<id>myApp</id>
<formats>
<format>zip</format>
</formats>
<dependencySets>
<dependencySet>
<useTransitiveDependencies>false</useTransitiveDependencies>
<includes><include>*:struts2-spring-plugin:jar:2.1.6</include></includes>
</dependencySet>
</dependencySets>
</assembly>

There is a workaround for this, if you set the scope of a dependency to runtime, transitive dependencies will be excluded. Though be aware this means you need to add in additional processing if you want to package the runtime dependency.
To include the runtime dependency in any packaging, you can use the maven-dependency-plugin's copy goal for a specific artifact.

If you develop under Eclipse, you can in the POM Editor (advanced tabs enabled) dependency graph look for the dependency you want to exclude of your project and then:
right click on it -> "Exclude Maven Artifact ..." and Eclipse will make the exclusion for you without the need to find out on which dependency the lib is linked.

What is your reason for excluding all transitive dependencies?
If there is a particular artifact (such as commons-logging) which you need to exclude from every dependency, the Version 99 Does Not Exist approach might help.
Update 2012: Don't use this approach. Use maven-enforcer-plugin and exclusions. Version 99 produces bogus dependencies and the Version 99 repository is offline (there are similar mirrors but you can't rely on them to stay online forever either; it's best to use only Maven Central).

In a simular issue I had the desired dependency declared with scope provided.
With this approach the transitive dependencies are fetched but are NOT included in the package phase, which is what you want.
I also like this solution in terms of maintenance, because there is no pom, or custom pom as in whaley's solution, needed to maintain; you only need to provide the specific dependency in the container and be done

Use the latest maven in your classpath.. It will remove the duplicate artifacts and keep the latest maven artifact..

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