Gradle: Building a modularized library that is compatible with Java 8
OK, I finally got it working. In case anyone else wants to know how to do it, this is what I have done:
set the Java version to 8, so that the library will be usable by Java 8 applications:
sourceCompatibility = 8
targetCompatibility = 8configure the module name
ext.moduleName
=com.dua3.utility
add a new sourceset consisting only of
module-info.java
:sourceSets { moduleInfo { java { srcDir 'src/module-info/java' } } }
set compatibility to Java 9 for the moduleInfo, sourceSet, configure modules, and set the output directory:
compileModuleInfoJava { sourceCompatibility = 9 targetCompatibility = 9 inputs.property("moduleName", moduleName) doFirst { classpath += sourceSets.main.compileClasspath options.compilerArgs = [ '--module-path', classpath.asPath, '--add-modules', 'ALL-SYSTEM,org.apache.logging.log4j', '-d', sourceSets.main.output.classesDirs.asPath ] } }
configure the
jar
task to includemoduleInfo
:jar { from sourceSets.main.output from sourceSets.moduleInfo.output }
In case you are using the SpotBugs
plugin, you also have to configure the sourceSet explicitly because it will otherwise fail when it tries to process the ModuleInfo sourceSet.
I finally ended up with this version of build.gradle
:
plugins {
id "com.github.spotbugs" version "1.6.0"
}
apply plugin: 'maven'
apply plugin: 'maven-publish'
apply plugin: 'java-library'
apply plugin: 'com.github.spotbugs'
sourceCompatibility = 8
targetCompatibility = 8
group = 'com.dua3.utility'
repositories {
mavenLocal()
jcenter()
}
dependencies {
compile group: 'org.apache.logging.log4j', name: 'log4j-api', version: '2.10.0'
testRuntime group: 'org.apache.logging.log4j', name: 'log4j-core', version: '2.10.0'
// Use JUnit test framework
testImplementation 'junit:junit:4.12'
}
ext.moduleName = 'com.dua3.utility'
sourceSets {
moduleInfo {
java {
srcDir 'src/module-info/java'
}
}
}
compileModuleInfoJava {
sourceCompatibility = 9
targetCompatibility = 9
inputs.property("moduleName", moduleName)
doFirst {
classpath += sourceSets.main.compileClasspath
options.compilerArgs = [
'--module-path', classpath.asPath,
'--add-modules', 'ALL-SYSTEM',
'-d', sourceSets.main.output.classesDirs.asPath
]
}
}
jar
{
from sourceSets.main.output
from sourceSets.moduleInfo.output
}
spotbugs {
sourceSets = [sourceSets.main]
}
tasks.withType(com.github.spotbugs.SpotBugsTask) {
reports {
xml.enabled false
html.enabled true
}
}
task sourcesJar(type: Jar, dependsOn: classes) {
classifier = 'sources'
from sourceSets.main.allSource
}
task javadocJar(type: Jar, dependsOn: javadoc) {
classifier = 'javadoc'
from javadoc.destinationDir
}
artifacts {
archives sourcesJar
archives javadocJar
}
defaultTasks 'build', 'publishToMavenLocal', 'install'
The question is over a year old, but in case anyone stumbles here, this functionality is now supported by Gradle Modules Plugin since version 1.5.0.
With this plugin, you don't have to create a custom source set, and you only need to call modularity.mixedJavaRelease
method.
Here's a sample of how to apply the plugin to one's main build.gradle
:
plugins {
// your remaining plugins here
id 'org.javamodularity.moduleplugin' version '1.5.0' apply false
}
subprojects {
// your remaining subproject configuration here
apply plugin: 'org.javamodularity.moduleplugin'
modularity.mixedJavaRelease 8 // sets "--release 8" for main code, and "--release 9" for "module-info.java"
// test.moduleOptions.runOnClasspath = true // optional (if you want your tests to still run on classpath)
}