[[managing-dependencies]]
== Managing Dependencies
To manage dependencies in your Spring Boot application, you can either apply the {dependency-management-plugin}[`io.spring.dependency-management`] plugin or, if you are using Gradle 6 or later, use Gradle's native bom support.
The primary benefit of the former is that it offers property-based customization of managed versions, while using the latter will likely result in faster builds.



[[managing-dependencies-dependency-management-plugin]]
=== Managing Dependencies with the Dependency Management Plugin
When you apply the {dependency-management-plugin}[`io.spring.dependency-management`] plugin, Spring Boot's plugin will automatically <<reacting-to-other-plugins-dependency-management,import the `spring-boot-dependencies` bom>> from the version of Spring Boot that you are using.
This provides a similar dependency management experience to the one that's enjoyed by Maven users.
For example, it allows you to omit version numbers when declaring dependencies that are managed in the bom.
To make use of this functionality, declare dependencies in the usual way but omit the version number:

[source,groovy,indent=0,subs="verbatim",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/dependencies.gradle[tags=dependencies]
----

[source,kotlin,indent=0,subs="verbatim",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/dependencies.gradle.kts[tags=dependencies]
----



[[managing-dependencies-dependency-management-plugin-customizing]]
==== Customizing Managed Versions
The `spring-boot-dependencies` bom that is automatically imported when the dependency management plugin is applied uses properties to control the versions of the dependencies that it manages.
Browse the {version-properties-appendix}[`Dependency versions Appendix`] in the Spring Boot reference for a complete list of these properties.

To customize a managed version you set its corresponding property.
For example, to customize the version of SLF4J which is controlled by the `slf4j.version` property:

[source,groovy,indent=0,subs="verbatim",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/custom-version.gradle[tags=custom-version]
----

[source,kotlin,indent=0,subs="verbatim",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/custom-version.gradle.kts[tags=custom-version]
----

WARNING: Each Spring Boot release is designed and tested against a specific set of third-party dependencies.
Overriding versions may cause compatibility issues and should be done with care.



[[managing-dependencies-dependency-management-plugin-using-in-isolation]]
==== Using Spring Boot's Dependency Management in Isolation

Spring Boot's dependency management can be used in a project without applying Spring Boot's plugin to that project.
The `SpringBootPlugin` class provides a `BOM_COORDINATES` constant that can be used to import the bom without having to know its group ID, artifact ID, or version.

First, configure the project to depend on the Spring Boot plugin but do not apply it:

ifeval::["{spring-boot-artifactory-repo}" == "release"]
[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/depend-on-plugin-release.gradle[]
----

[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/depend-on-plugin-release.gradle.kts[]
----
endif::[]
ifeval::["{spring-boot-artifactory-repo}" == "milestone"]
[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/depend-on-plugin-milestone.gradle[]
----
[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/depend-on-plugin-release.gradle.kts[]
----
endif::[]
ifeval::["{spring-boot-artifactory-repo}" == "snapshot"]
[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/depend-on-plugin-snapshot.gradle[]
----
[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/depend-on-plugin-release.gradle.kts[]
----
endif::[]

The Spring Boot plugin's dependency on the dependency management plugin means that you can use the dependency management plugin without having to declare a dependency on it.
This also means that you will automatically use the same version of the dependency management plugin as Spring Boot uses.

Apply the dependency management plugin and then configure it to import Spring Boot's bom:

[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/configure-bom.gradle[tags=configure-bom]
----

[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/configure-bom.gradle.kts[tags=configure-bom]
----


The Kotlin code above is a bit awkward.
That's because we're using the imperative way of applying the dependency management plugin.

We can make the code less awkward by applying the plugin from the root parent project, or by using the `plugins` block as we're doing for the Spring Boot plugin.
A downside of this method is that it forces us to specify the version of the dependency management plugin:

[source,kotlin,indent=0,subs="verbatim,attributes"]
----
include::../gradle/managing-dependencies/configure-bom-with-plugins.gradle.kts[tags=configure-bom]
----



[[managing-dependencies-dependency-management-plugin-learning-more]]
==== Learning More
To learn more about the capabilities of the dependency management plugin, please refer to its {dependency-management-plugin-documentation}[documentation].



[[managing-dependencies-gradle-bom-support]]
=== Managing Dependencies with Gradle's Bom Support
Gradle allows a bom to be used to manage a project's versions by declaring it as a `platform` or `enforcedPlatform` dependency.
A `platform` dependency treats the versions in the bom as recommendations and other versions and constraints in the dependency graph may cause a version of a dependency other than that declared in the bom to be used.
An `enforcedPlatform` dependency treats the versions in the bom as requirements and they will override any other version found in the dependency graph.

The `SpringBootPlugin` class provides a `BOM_COORDINATES` constant that can be used to declare a dependency upon Spring Boot's bom without having to know its group ID, artifact ID, or version, as shown in the following example:

[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/configure-platform.gradle[tags=configure-platform]
----

[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/configure-platform.gradle.kts[tags=configure-platform]
----

A platform or enforced platform will only constrain the versions of the configuration in which it has been declared or that extend from the configuration in which it has been declared.
As a result, in may be necessary to declare the same dependency in more than one configuration.



[[managing-dependencies-gradle-bom-support-customizing]]
==== Customizing Managed Versions
When using Gradle's bom support, you cannot use the properties from `spring-boot-dependencies` to control the versions of the dependencies that it manages.
Instead, you must use one of the mechanisms that Gradle provides.
One such mechanism is a resolution strategy.
SLF4J's modules are all in the `org.slf4j` group so their version can be controlled by configuring every dependency in that group to use a particular version, as shown in the following example:

[source,groovy,indent=0,subs="verbatim",role="primary"]
.Groovy
----
include::../gradle/managing-dependencies/custom-version-with-platform.gradle[tags=custom-version]
----

[source,kotlin,indent=0,subs="verbatim",role="secondary"]
.Kotlin
----
include::../gradle/managing-dependencies/custom-version-with-platform.gradle.kts[tags=custom-version]
----

WARNING: Each Spring Boot release is designed and tested against a specific set of third-party dependencies.
Overriding versions may cause compatibility issues and should be done with care.
