Home » Enterprise Java » Maven » How to Use Maven For Dependency Management

About Yogesh Mali

Yogesh currently lives in Minneapolis and works as a Senior Software Engineer. He has a masters degree in Computer Science from University of Minnesota, Twin Cities. At graduate school, he did research in programming languages because of his love for functional and object oriented programming. Currently he delves into more details of Java, web development and security. Previously he worked as a product manager to create web application for health insurance brokers. In his free time, he listens to music and writes fictional stories.

How to Use Maven For Dependency Management

In this example, we will see how to use Maven for dependency management. Maven is a build manager tool and mostly used in java projects. Maven was built on a central concept of project object model (POM). Maven addresses two steps for any project – first how a project is built and second how the dependencies are described.

1. Environment

  1. Windows 7 SP 1
  2. Eclipse Kepler 4.3
  3. Maven 3.0.4
  4. Java version 7

2. Maven for Dependency Management

Maven is used in large projects for one of its major feature and that is dependency management. Maven just not supports dependencies for a single project, but it easily manages multi-module projects. In such projects, maven helps in maintaining a high degree of control and stability.

3. Transitive Dependency

This feature of Transitive Dependency allows to avoid needing to discover and specify libraries that your own dependencies require, and what that means is that if your project is dependent on some libraries and those libraries are dependent on other libraries, you only specify your project’s dependencies and this feature takes care of other dependencies. There is no limit to levels that dependencies can be gathered from, and will only cause a problem if cyclic dependency is discovered. If your project depends on A and A depends on C and C depends on B and B depends on A .

Following features help to limit the graph of included libraries using transitive dependencies’ feature:

  • Dependency Mediation – This feature determines what version of a dependency will be used when multiple versions of an artifact are encountered. You can always guarantee a version by declaring it explicitly in project’s POM. If two dependency versions are at the same depth in the dependency tree, the order in the declaration that counts, the first declaration wins.
  • Dependency Management – With this feature, you can specify versions of artifacts to be used when they are encountered in transitive dependencies.
  • Dependency Score – This allows you to only include dependencies appropriate for the current stage of the build.
  • Excluded Dependencies – If project X depends on project Y, and project Y depends on project Z, the project X can explicitly exclude project Z as a dependency using the exclusion element.
  • Optional Dependencies – If project Y depends on project Z, and the owner of Project Y can mark project Z as optional dependency, using the optional element. When project X depends on project Y, X will depend only on Y and not on Y’s optional dependency Z.

4. Dependency Scope

Dependency scope is used to restrict the transitivity of a dependency, and also to affect the classpath used for various build. There are 6 scopes available:

    1. Compile – This is the default scope if any is indicated. The dependencies are available in all classpaths of a project.
    2. provided – This is used when JDK or a web container is going to provide a dependency at runtime.
    3. runtime – This scope indicates that the dependency is not required for compilation, but for runtime.
    4. test – This scope indicates the dependency is required during test compilation and execution phases.
    5. system – This scope is similar to provided except that you have to provide JAR which contains in explicitly.
    6. import – This is used inside a dependencymanagement tag. It indicates that the specified POM should be replaced with the dependencies in that POM’s dependencymanagement section.

5. Dependency Management

Dependency management is a mechanism to centralize the dependency information. In a multi-module project, you can specify in a parent project all the artifact version and it will be inherited by the child projects.

Below we will see an example where there are two POMs which extend the same parent.

project A

<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>com.javacodegeeks.example</groupId>
	<artifactId>java-code-geeks-parent-A</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>

	<dependencies>
	<dependency>
        <groupId>group-a</groupId>
        <artifactId>artifact-a</artifactId>
        <version>1.0</version>
        <exclusions>
        <exclusion>
        <groupId> group-c </groupId>
        <artifactId>excluded-artifact</artifactId>
        </exclusion>
        </exclusions>
	</dependency>
     <dependency>
      <groupId>group-a</groupId>
      <artifactId>artifact-b</artifactId>
      <version>1.0</version>
      <type>bar</type>
      <scope>runtime</scope>
      </dependency>
     </dependencies>
</project>

project B

<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>
	<artifactId>java-code-geeks-parent-B</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>
	
	  <dependencies>
    <dependency>
      <groupId>group-c</groupId>
      <artifactId>artifact-b</artifactId>
      <version>1.0</version>
      <type>war</type>
      <scope>runtime</scope>
    </dependency>
    <dependency>
      <groupId>group-a</groupId>
      <artifactId>artifact-b</artifactId>
      <version>1.0</version>
      <type>bar</type>
      <scope>runtime</scope>
    </dependency>
  </dependencies>
</project>

These two POMs share a common dependency and each has one non-trivial dependency. Now parent POM will look like below

Parent Project

<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>com.java.code.geeks</groupId>
	<artifactId>java-code-geeks-parent</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>
<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>group-a</groupId>
        <artifactId>artifact-a</artifactId>
        <version>1.0</version>
 
        <exclusions>
          <exclusion>
            <groupId>group-c</groupId>
            <artifactId>excluded-artifact</artifactId>
          </exclusion>
        </exclusions>
 
      </dependency>
 
      <dependency>
        <groupId>group-c</groupId>
        <artifactId>artifact-b</artifactId>
        <version>1.0</version>
        <type>war</type>
        <scope>runtime</scope>
      </dependency>
 
      <dependency>
        <groupId>group-a</groupId>
        <artifactId>artifact-b</artifactId>
        <version>1.0</version>
        <type>bar</type>
        <scope>runtime</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>

</project>

And two child POMs will be like below

Child A

<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>com.javacodegeeks.example</groupId>
	<artifactId>java-code-geeks-child-A</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>
	  <dependencies>
    <dependency>
      <groupId>group-a</groupId>
      <artifactId>artifact-a</artifactId>
    </dependency>
 
    <dependency>
      <groupId>group-a</groupId>
      <artifactId>artifact-b</artifactId>
      <type>bar</type>
    </dependency>
  </dependencies>
</project>	

Child B

<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>com.java.code.geeks</groupId>
	<artifactId>java-code-geeks-child-B</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>
  <dependencies>
    <dependency>
      <groupId>group-c</groupId>
      <artifactId>artifact-b</artifactId>
      
      <type>war</type>
    </dependency>
 
    <dependency>
      <groupId>group-a</groupId>
      <artifactId>artifact-b</artifactId>

      <type>bar</type>
    </dependency>
  </dependencies>	
</project>

6. System Dependencies

System dependencies are specified with systemPath under system scope and they are always available and are not looked up in repository. They tell Maven about dependencies which are provided by JDK or VM. A simple example as below shows that of JDBC extension:

<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>com.javacodegeeks.example</groupId>
	<artifactId>java-code-geeks-jdbcexample</artifactId>
	<version>1.0.1</version>
	<packaging>pom</packaging>
      <dependencies>
        <dependency>
          <groupId>javax.sql</groupId>
          <artifactId>jdbc-stdext</artifactId>
          <version>2.0</version>
          <scope>system</scope>
          <systemPath>${java.home}/lib/rt.jar</systemPath>
        </dependency>
      </dependencies>
    </project>

7. Conclusion

Maven has provided a powerful capabilities to developer to manage their multi-projects under one roof. In this example, we saw how to use Maven for dependency management.

8. Related Articles

    1. Maven Introduction

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

I have read and agree to the terms & conditions

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments