Spring has long been the dominant Java web framework, while Gradle has solidified its position as a preferred build tool among developers. You'd think combining these two technologies would be straightforward, right? Yet, developers often find themselves ensnared in dependency management issues that can be tricky to navigate. This guide aims to provide a comprehensive walkthrough for effectively managing Spring dependencies in Gradle, addressing common pitfalls, and highlighting best practices to keep your builds smooth and error-free.

Understanding Spring and Gradle

Most Spring applications bring together multiple Spring projects, like Spring Boot and Spring Security, along with other essential libraries. Managing versions manually can be a nightmare, especially when dealing with the intricate web of transitive dependencies.

This is where the concept of a Bill of Materials (BOM) comes into play. A BOM is a special POM file that groups a set of dependencies with predefined versions, simplifying the process of version management. Fortunately, Gradle has built-in support for BOM imports, saving you from potential version mismatches and conflicts.

The Importance of BOMs

By using a BOM, you can import a pre-defined set of dependencies with specified versions, ensuring compatibility and making your life easier. Imagine the chaos of manually managing versions for dozens of dependencies in a large Spring application. Using a BOM simplifies this by centralizing version definitions, making your build file cleaner and easier to maintain.

Setting Up BOMs in Gradle

Gradle introduced BOM support in version 5.0 (November 2018). Prior to this, developers had to rely on the io.spring.dependency-management plugin. Using this plugin is still common practice, but native BOM support offers a more streamlined approach.

Using the Dependency Management Plugin

Here is a typical build script using the io.spring.dependency-management plugin:


buildscript {
repositories {
jcenter()
}
dependencies {
classpath('org.springframework.boot:spring-boot-gradle-plugin:2.1.0.RELEASE')
}
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

repositories {
jcenter()
}

dependencies {
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-security'
}


This works fine for basic setups but can lead to issues with more complex configurations, such as overriding transitive dependencies.

The Native Gradle Approach

With native BOM support, your build script becomes simpler and easier to manage. Here's how you can do it:


plugins {
id 'java'
id 'org.springframework.boot' version '2.1.0.RELEASE'
}

repositories {
jcenter()
}

dependencies {
implementation platform('org.springframework.boot:spring-boot-dependencies:2.1.0.RELEASE')
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-security'
}


This approach leverages Gradle's built-in mechanism for dependency management, making it easier to control and understand what happens in case of a conflict.

Handling Critical Vulnerabilities

Imagine a situation where a critical security vulnerability is discovered in one of your dependencies, such as Jackson Databind. You'll want to push a patched version immediately, without waiting for a new Spring release. Here’s how you can manage such a situation:

Using the Plugin


dependencies {
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-security'
constraints {
implementation('com.fasterxml.jackson.core:jackson-databind:2.10.1') {
because 'versions below are vulnerable to CVE-2019-16942'
}
}
}


However, you might still end up with the older, vulnerable version due to the plugin's internal workings. This happens because the plugin overrides the native Gradle version conflict resolution strategy.

Native Gradle Method


dependencies {
implementation platform('org.springframework.boot:spring-boot-dependencies:2.1.0.RELEASE')
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-security'
constraints {
implementation('com.fasterxml.jackson.core:jackson-databind:2.10.1') {
because 'versions below are vulnerable to CVE-2019-16942'
}
}
}


This ensures that the desired version is selected, utilizing Gradle’s conflict resolution mechanism effectively.

Multi-Project Builds

Managing dependencies in a multi-project Gradle build can be challenging, especially when dealing with Spring Boot and its various modules.

Using the Plugin

Here’s a multi-project setup using the io.spring.dependency-management plugin:


buildscript {
repositories {
jcenter()
}
dependencies {
classpath('org.springframework.boot:spring-boot-gradle-plugin:2.1.0.RELEASE')
}
}

allprojects {
apply plugin: 'java'
apply plugin: 'io.spring.dependency-management'

repositories {
jcenter()
}

dependencyManagement {
imports {
mavenBom 'org.springframework.boot:spring-boot-dependencies:2.1.0.RELEASE'
}
}
}

apply plugin: 'org.springframework.boot'

dependencies {
implementation project(":core")
implementation "org.springframework.boot:spring-boot-starter-web"
}


This configuration separates the dependency management configuration from the Spring Boot plugin, but it can still become cumbersome.

Native Gradle Approach


plugins {
id 'java-library'
id 'org.springframework.boot' version '2.1.0.RELEASE'
}

allprojects {
apply plugin: 'java-library'

repositories {
jcenter()
}
}

dependencies {
implementation project(':core')
implementation 'org.springframework.boot:spring-boot-starter-web'
}


In this configuration, importing the BOM at the root of the project allows its transitive dependencies to be propagated, simplifying the build script and making it easier to manage.

Consistent Version Management

Managing the versions of related libraries consistently can be crucial, particularly for libraries like Jackson that consist of multiple components.

Using Virtual Platforms


dependencies {
components.all(JacksonAlignmentRule)
implementation platform('org.springframework.boot:spring-boot-dependencies:2.1.0.RELEASE')

implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-security'
constraints {
implementation('com.fasterxml.jackson.core:jackson-databind:2.10.1') {
because 'versions below are vulnerable to CVE-2019-16942'
}
}
}

class JacksonAlignmentRule implements ComponentMetadataRule {
void execute(ComponentMetadataContext ctx) {
ctx.details.with {
if (id.group.startsWith('com.fasterxml.jackson')) {
belongsTo("com.fasterxml.jackson:jackson-platform:${id.version}")
}
}
}
}


This ensures that all Jackson dependencies are aligned to the same version, leveraging Gradle’s component metadata rules.

Conclusion

While the io.spring.dependency-management plugin is widely recommended and used, the latest Gradle versions offer native BOM support that fits better into the Gradle build model. Embracing these newer features can result in more concise and maintainable build scripts, reducing the burden of managing complex dependency trees in your Spring applications.