当我们已经使用 id “org.springframework.boot” 插件时，我们是否需要 “io.spring.dependency-management” gradle 插件

Question

What happens when spring-boot plugin is added to Gradle project? Why do we need to explicitly include spring.dependency-management plugin also.?

plugins {
    id "org.springframework.boot" version "2.1.5.RELEASE"
    id 'io.spring.dependency-management' version '1.0.8.RELEASE'
}

Answer 1

Since Gradle 5+ supports BOM files, you don't need the dependency-management plugin anymore. The spring boot plugin is still needed to provide tasks such as bootJar and bootRun . Here's a minimal build.gradle that should work:

buildscript {
    ext {
        springBootVersion = '2.2.4.RELEASE'
    }
}

repositories {
    mavenCentral()
}

plugins {
    id 'java'
    id 'org.springframework.boot' version "${springBootVersion}"
}

dependencies {
    implementation platform("org.springframework.boot:spring-boot-dependencies:${springBootVersion}")
    implementation 'org.springframework.boot:spring-boot-starter'
    implementation 'org.springframework.boot:spring-boot-starter-webflux'
    testImplementation('org.springframework.boot:spring-boot-starter-test') {
        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
    }
}

Answer 2

Why Spring Boot Gradle Plugin

To paraphrase Spring Boot Gradle Plugin Reference Guide :

The Spring Boot Gradle Plugin provides Spring Boot support in Gradle. It allows you to package executable jar or war archives, run Spring Boot applications, and use the dependency management provided by spring-boot-dependencies.

The key point to note is, apart from providing Spring Boot support, it enables the use of dependency management through spring-boot-dependencies. But...

Why Spring Dependency Management Plugin

The spring-boot-dependencies BOM enables dependency management.

Which means:

1. IF you omit the version for a dependency you declare:
2. AND it is a managed dependency (ie listed in the BOM with version):
3. THEN (provided you apply the spring-boot-dependencies plugin) you get to enjoy dependency management like in Maven

To get the dependencies bom in your project you have to apply the dependency-management plugin in concert with the Spring boot gradle plugin. Again to paraphrase

When you apply the io.spring.dependency-management plugin, Spring Boot's plugin will automatically import the spring-boot-dependencies bom from the version of Spring Boot that you are using.

Why one or the other?

If you need Spring Boot support, you want that plugin.

In addition, if you want managed dependencies (as explained above), you want the dependency-management plugin.

Another way to have dependency constraints

The dependency-management plugin is one way to import the Spring Boot bill of materials (BOM).

Another way (supported by Gradle 5 and up) is to import recommended dependency versions from a BOM as dependency constraints in Gradle. The "platform" (dependency handler method) is used to import the BOM.

dependencies {
    // Load BOM for Spring Boot.
    implementation(platform("org.springframework.boot:spring-boot-dependencies:2.3.0.RELEASE"))
}

Using either way of dependency management, you can specify your dependencies without an explicit version, as below:

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-mongodb'
}

Answer 3

The migration guide gives some hints about this:

Spring Boot's Gradle plugin no longer automatically applies the dependency management plugin. Instead, Spring Boot's plugin now reacts to the dependency management plugin being applied by importing the correct version of the spring-boot-dependencies BOM. This gives you more control over how and when dependency management is configured.

For most applications applying the dependency management plugin will be sufficient:

 apply plugin: 'org.springframework.boot' apply plugin: 'io.spring.dependency-management' // <-- add this to your build.gradle

Note: The dependency management plugin remains a transitive dependency of spring-boot-gradle-plugin so there's no need for it to be listed as a classpath dependency in your buildscript configuration.

https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.0-Migration-Guide#dependency-management