Installing Java JDK 21 (MacOS)

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Installing the newly released JDK 21 LTS release on MacOS is rather straightforward, but requires a couple of non-intuitive steps; also, current support for Gradle builds is “tentative” at best, so we will show below a simple way to upgrade your Spring Boot application(s).

Download the JDK from here (if you are using a recent-ish MacBookPro with Apple Silicon, M1 or M2, choose the macOS / AArch64 variant; for older versions with Intel silicon, macOS / x64 should work just fine).

The JDKs are installed (on MacOS) in /Library/Java/JavaVirtualMachines:

└─( lsjava
21 /Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home
20.0.2 /Library/Java/JavaVirtualMachines/jdk-20.0.2.jdk/Contents/Home
17.0.2 /Library/Java/JavaVirtualMachines/jdk-17.0.2.jdk/Contents/Home

where

alias lsjava='/usr/libexec/java_home -X | \
    plutil -convert json -o - - | \
    jq ".[] | .JVMVersion + \" \" + .JVMHomePath" | \
    sed "s/\"//g"'

is a little shortcut of mine, to quickly find what’s where (on my machine I also keep older JDKs, including 8 and 11, the main LTS releases).

Once downloaded and unzipped the tarball, move the folder to its final resting place and update JAVA_HOME:

└─( sudo mv Downloads/jdk-21.jdk /Library/Java/JavaVirtualMachines

└─( export JAVA_HOME=$(/usr/libexec/java_home -v 21)

└─( java -version
openjdk version "21" 2023-09-19
OpenJDK Runtime Environment (build 21+35-2513)
OpenJDK 64-Bit Server VM (build 21+35-2513, mixed mode, sharing)

to make the change “stick,” you may want to add that export JAVA_HOME line in your .zshrc file.

Finally, update IntelliJ installed JDKs:

Right-click on the module name in the Project view and select `Open Module Settings`

The most recent Gradle release (8.4) does support building using Java 21, so, the first step is to upgrade the downloaded “wrapper”: change to your project’s folder and run:

./gradlew wrapper --gradle-version=8.4 --distribution-type=bin

which will nicely update the entry in your gradle/gradle-wrapper.properties:

distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-bin.zip

However, that won’t really help much, and depending on your setup/configuration/dependencies, trying to run ./gradlew clean build will most likely fail.

In my simple Spring Boot CLI demo app, I updated my build.gradle to look as follows (the full commit is here):

plugins {
    id 'application'
    id 'org.springframework.boot' version '3.1.4'
    id 'io.spring.dependency-management' version '1.1.3'
    id 'java'
}

java {
    sourceCompatibility = '21'
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

ext {
    // see note below
    lombokVersion = "1.18.30"
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'

    // Lombok
    compileOnly "org.projectlombok:lombok:${lombokVersion}"
    annotationProcessor "org.projectlombok:lombok:${lombokVersion}"

    // For the @PostConstruct annotation
    implementation 'javax.annotation:javax.annotation-api:1.3.2'
}

Simplified `build.gradle` to support JDK 21

This is all pretty self-explanatory (and rather unsurprising) apart from the Lombok needed upgrade – any version prior to .30 will cause a rather confusing error:

Fatal error compiling: java.lang.NoSuchFieldError:
Class com.sun.tools.javac.tree.JCTree$JCImport does not have member field 'com.sun.tools.javac.tree.JCTree qualid'

which is 🤷🏼

Having done all the above:

└─( gw clean build test
OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended

> Task :app:test


BUILD SUCCESSFUL in 2s
15 actionable tasks: 15 executed

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