Maven <dependency>

Mental model (remember this)

<dependency> defines what, when, and how far a library is visible

• what → groupId / artifactId / classifier
• when → scope
• how far → optional / exclusions

Maven <dependency> — All Children Explained

Full form:

<dependency>
  <groupId>...</groupId>
  <artifactId>...</artifactId>
  <version>...</version>
  <type>...</type>
  <classifier>...</classifier>
  <scope>...</scope>
  <optional>...</optional>
  <exclusions>...</exclusions>
</dependency>

1️⃣ <groupId> (REQUIRED)

What it is

The organization / namespace of the artifact.

<groupId>org.springframework</groupId>

Rules

• Usually a reversed domain name
• Maps directly to directory path

org.springframework → org/springframework

2️⃣ <artifactId> (REQUIRED)

What it is

The name of the artifact.

<artifactId>spring-context</artifactId>

Rules

• Unique within the groupId
• No version, no classifier here

3️⃣ <version> (CONDITIONALLY REQUIRED)

What it is

The exact version of the dependency.

• Exact artifact version
• Can be omitted if managed elsewhere

<version>5.3.30</version>

When it’s optional

If controlled by:

• dependencyManagement
• a BOM
• parent POM

Best practice

✔ Centralize versions
❌ Hardcode everywhere

4️⃣ <type> (OPTIONAL)

What it is

The artifact packaging type.

Default:

jar

Common values

Example (BOM import)

<type>pom</type>

5️⃣ <classifier> (OPTIONAL, ADVANCED)

What it is

A variant of the same artifact.

Example:

guava-31.1-jre.jar
guava-31.1-android.jar

Usage

<classifier>sources</classifier>

Common classifiers:

• sources
• javadoc
• tests
• linux-x86_64

⚠️ Use only if you know what you’re doing.

6️⃣ <scope> (VERY IMPORTANT)

What it is

Controls where and when the dependency is used.

All scopes explained

compile (DEFAULT)

• Available everywhere
• Included transitively

<scope>compile</scope>

provided

• Needed to compile
• Not packaged
• Provided by runtime (e.g. servlet container)

<scope>provided</scope>

runtime

• Not needed to compile
• Needed at runtime

<scope>runtime</scope>

test

• Only for tests
• Not transitive

<scope>test</scope>

system (AVOID)

• Hardcoded local path
• Breaks portability

<scope>system</scope>
<systemPath>/lib/foo.jar</systemPath>

import (SPECIAL)

• Only valid in dependencyManagement
• Used for BOMs

<scope>import</scope>

7️⃣ <optional> (MISUNDERSTOOD)

What it is

Prevents this dependency from being pulled transitively.

<optional>true</optional>

What it does NOT do

❌ Does not remove the dependency from your build
❌ Does not make it runtime-optional

When to use

Libraries that support plug-ins or extensions.

8️⃣ <exclusions> (CONFLICT CONTROL)

What it is

Explicitly removes unwanted transitive dependencies.

<exclusions>
  <exclusion>
    <groupId>commons-logging</groupId>
    <artifactId>commons-logging</artifactId>
  </exclusion>
</exclusions>

Use cases

• Resolve conflicts
• Remove legacy libs
• Replace logging frameworks

⚠️ Overuse leads to fragile builds.

9️⃣ Hidden but related elements

<systemPath> (ONLY with system)

<systemPath>${project.basedir}/lib/foo.jar</systemPath>

❌ Strongly discouraged.