In this article, we will explore Gradle Toolchains support for JVM projects. Gradle is a powerful build automation tool that provides a flexible and extensible way to build, test, and package software projects. Toolchains support in Gradle allows developers to specify and manage different versions of the Java Development Kit (JDK) or other tools required by their projects. This feature is particularly useful when working with projects that need to be built and executed using a specific JDK version.
1. Introduction
Gradle Toolchains is a feature introduced in Gradle 6.7 that allows developers to specify and manage different versions of tools required by their projects. This feature is particularly useful when working with JVM projects that need to be built and executed using a specific JDK version.
Prior to the introduction of Toolchains support, developers typically relied on configuring the JDK version using environment variables or project-specific configurations. However, this approach had limitations and required manual setup for each development environment.
With Toolchains support, Gradle provides a declarative way to define and manage the JDK version or other tools required by the project. It enables developers to automate the selection and configuration of the appropriate tool versions, making the build process more reliable and reproducible across different development environments.
In the following sections, we will explore how to configure and use Toolchains in Gradle for JVM projects. We will cover scenarios such as compiling, testing, and packaging the project with a specific JDK version. We will also discuss advanced configurations and custom toolchain providers for supporting non-JDK tools.
2. Configuring Toolchains in Gradle
Configuring Toolchains in Gradle involves defining the available toolchains and declaring the toolchain requirements in the project’s build configuration. The toolchain requirements specify the desired tool versions for different tasks, such as compilation, testing, or packaging. Gradle then selects the appropriate toolchain based on the requirements and configures the project accordingly.
2.1. Defining a Toolchain
To define a toolchain in Gradle, you need to specify the tool’s type and the installation path. The installation path can be a directory or a symbolic link to the tool’s executable.
Here’s an example of defining a JDK toolchain in Gradle:
java {
toolchain {
languageVersion = JavaLanguageVersion.of(11)
vendor = 'adoptopenjdk'
distribution = 'temurin'
}
}In the above example, we define a JDK toolchain with language version 11. We also specify the vendor and distribution names to identify the specific JDK distribution to use. Gradle supports various vendors and distributions, such as ‘adoptopenjdk’, ‘zulu’, ‘amazon-corretto’, ‘temurin’, and more.
2.2. Declaring a Toolchain Requirement
Once you have defined the available toolchains, you can declare toolchain requirements in the project’s build configuration. Toolchain requirements can be declared for different tasks or actions, such as compilation, testing, or packaging.
To declare a toolchain requirement, you use the with block inside the task configuration:
tasks.withType(JavaCompile) {
options.fork = true
options.forkOptions.executable = toolchains.java?.executable('javac')
}In the above example, we configure the JavaCompile task to use a toolchain-provided javac executable. The toolchains.java property provides the selected Java toolchain for the project. By setting the executable property of the forkOptions, we instruct Gradle to use the specified toolchain-provided javac executable for compilation.
2.3. Selecting a Toolchain
Gradle automatically selects the appropriate toolchain based on the declared requirements. It matches the required tool versions with the available toolchains and selects the best match.
To ensure Gradle selects the desired toolchain, you can use the java.toolchains.registerOldJdkDetection configuration:
java.toolchains.registerOldJdkDetection {
minimumVersion = JavaLanguageVersion.of(8)
maximumVersion = JavaLanguageVersion.of(11)
runtimeFallbacks {
JavaLanguageVersion.of(8)
}
}In the above example, we define a toolchain detection configuration that selects toolchains with a minimum version of 8 and a maximum version of 11. We also specify a runtime fallback to use Java 8 if no matching toolchain is found.
By configuring the toolchain detection, you can control which toolchains Gradle considers during selection. This ensures compatibility with the specified JDK versions and allows fallback options if the desired toolchain is not available.
Now that we have covered the basics of configuring toolchains in Gradle, let’s explore how to use toolchains in JVM projects for compilation, testing, and packaging.
3. Using Toolchains in JVM Projects
In JVM projects, Gradle allows you to use toolchains for different tasks, such as compiling, testing, and packaging. In this section, we will explore how to use toolchains for these tasks and ensure the project is built and executed with the desired JDK version.
3.1. Compiling with a Specific JDK Version
To compile a JVM project with a specific JDK version, you can configure the JavaCompile task to use a toolchain-provided javac executable, as shown in the previous section.
Here’s an example of configuring the JavaCompile task to use a specific JDK version:
tasks.withType(JavaCompile) {
options.fork = true
options.forkOptions.executable = toolchains.java?.executable('javac')
}By setting the executable property of the forkOptions to the toolchain-provided javac executable, Gradle will compile the project using the specified JDK version.
3.2. Testing with a Specific JDK Version
Similarly, you can use toolchains to execute tests with a specific JDK version. The Test task in Gradle allows you to configure the test runtime environment, including the JDK version.
Here’s an example of configuring the Test task to use a specific JDK version:
tasks.withType(Test) {
jvmPlatform {
toolChain toolchains.java
}
}In the above example, we configure the Test task to use the Java toolchain selected by Gradle. By setting the toolChain property of the jvmPlatform block to toolchains.java, Gradle will execute the tests using the specified JDK version.
3.3. Packaging with a Specific JDK Version
In some cases, you may want to package your JVM project using a specific JDK version. Gradle provides the JavaPlugin and the Jar task for packaging Java projects into JAR files.
Here’s an example of configuring the Jar task to use a specific JDK version:
tasks.jar {
doFirst {
if (toolchains.java) {
project.logger.info("Packaging using JDK ${toolchains.java.languageVersion}")
manifest {
attributes(
'Main-Class': 'com.example.MainClass'
)
}
}
}
}In the above example, we check if the Java toolchain is available and log the JDK version being used for packaging. We also specify the main class in the JAR manifest.
By customizing the Jar task, you can ensure that your project is packaged using the desired JDK version specified in the toolchain.
4. Advanced Toolchains Configuration
In addition to the basic toolchains configuration, Gradle provides advanced features for customizing toolchain selection and supporting non-JDK tools. In this section, we will explore these advanced configurations.
4.1. Custom Toolchain Providers
By default, Gradle supports various JDK vendors and distributions out-of-the-box. However, you can also define custom toolchain providers to support additional JDK distributions or other tools.
Here’s an example of defining a custom toolchain provider for a JDK distribution:
java {
toolchain {
languageVersion = JavaLanguageVersion.of(11)
vendor = 'custom-jdk'
distribution = 'custom-jdk-distribution'
pathProvider { toolchain ->
'/path/to/custom-jdk'
}
}
}In the above example, we define a custom toolchain provider for a JDK distribution called ‘custom-jdk-distribution’. We specify the language version, vendor, and a custom path provider function that returns the installation path of the custom JDK.
By defining a custom toolchain provider, you can integrate Gradle with any JDK distribution or other tools that are not supported out-of-the-box.
4.2. Supporting Non-JDK Tools
Gradle Toolchains support is not limited to JDK versions. You can also use toolchains to manage other tools required by your project, such as different versions of Kotlin compiler or Android SDK.
Here’s an example of configuring the Kotlin compiler using a toolchain:
kotlin {
toolchain {
languageVersion = KotlinJvmLanguageVersion.of("1.5.0")
vendor = 'kotlinlang'
distribution = 'kotlin-compiler'
}
}In the above example, we configure the Kotlin compiler toolchain with the desired language version, vendor, and distribution. Gradle will select and use the specified Kotlin compiler version during the compilation of Kotlin sources.
Similarly, you can configure toolchains for other non-JDK tools required by your project, such as Android SDK for Android projects.
5. Conclusion
Gradle Toolchains support for JVM projects provides a powerful mechanism to manage and automate the selection of tool versions required by your project. With toolchains, you can ensure consistent builds across different development environments, eliminate manual setup, and easily switch between different JDK versions or other tools.
In this guide, we covered the basics of configuring and using toolchains in Gradle for JVM projects. We explored how to define toolchains, declare toolchain requirements, and use toolchains for compilation, testing, and packaging. We also discussed advanced configurations for custom toolchain providers and supporting non-JDK tools.
By leveraging Gradle Toolchains support, you can enhance the reliability, reproducibility, and flexibility of your JVM projects.
