Gradle

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Introduction into C++ Builds with Gradle

Shadow plugin: "Shadow is a Gradle plugin for combining a project's dependency classes and resources into a single output Jar. The combined Jar is often referred to a fat-jar or uber-jar. ... Shadowing a project output has 2 major use cases: (1) Creating an executable JAR distribution, and Bundling and relocating common dependencies in libraries to avoid classpath conflicts."

Reading

Building Java Projects with Gradle
Gradle Succinctly - José Roberto Olivas Mendoza
Gradle User Guide - Hans Dockter, Adam Murdoch (PDF)

Notes

Gradle uses a 1:1 relationship of a build script to a Project instance. Most "magic" comes from the use of plugins (listed below). Thus, the world's simplest Gradle build:

// build.gradle.kts
println("Hello Gradle")

... when run with gradle -b build.gradle.kts:

~/Projects/Exploration.git/Gradle % gradle -b build.gradle.kts 

> Configure project :
Hello Gradle

> Task :help

Welcome to Gradle 8.10.

To run a build, run gradle <task> ...

To see a list of available tasks, run gradle tasks

To see more detail about a task, run gradle help --task <task>

To see a list of command-line options, run gradle --help

For more detail on using Gradle, see https://docs.gradle.org/8.10/userguide/command_line_interface.html

For troubleshooting, visit https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.

You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.

For more on this, please refer to https://docs.gradle.org/8.10/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.

BUILD SUCCESSFUL in 843ms
1 actionable task: 1 executed

Customizing

Custom Task inside the build script

Wrote a custom task that invokes javap on compiled class files (here):

open class Javap: DefaultTask() {
    @Internal var workingDir = "./build/classes/java/main"
    @Internal var outputDir: String = ""
    @Internal lateinit var classFiles: List<String>
    @Internal lateinit var javapArguments: List<String>
    @Internal var projectDir = project.projectDir

    @TaskAction
    fun runCommand() {
        logger.warn("Running 'disasm' replaces the marked javap files with newly-generated content!")
        for (classFile in classFiles) {
            val commandLine = ("javap " + javapArguments.joinToString(" ") + " " + classFile)
            try {
                val workingDir = File(projectDir, workingDir)
                val outputDir = File(projectDir, outputDir)
                val parts = commandLine.split("\\s".toRegex())
                // Transform the classFile string/path to a dotted name
                val dottedClassFile = classFile.split("/").joinToString(".")
                val outputFile = File(outputDir, dottedClassFile + ".bytecode")
                val proc = ProcessBuilder(*parts.toTypedArray())
                        .directory(workingDir)
                        .redirectOutput(outputFile)
                        .redirectError(ProcessBuilder.Redirect.PIPE)
                        .start()

                proc.waitFor(60, TimeUnit.MINUTES)
                println("Success processing ${classFile}")
            } catch(e: Exception) {
                e.printStackTrace()
                println("Failure processing ${classFile}: ${e.message}")
            }
        }
    }
}

tasks.register<Javap>("disasm") {
    group = "build"
    description = "Produce disassembly listings of Java code"
    javapArguments = listOf("-v")
    outputDir = ""
    classFiles = listOf(
        "com/newardassociates/demo/App.class",
        "com/newardassociates/demo/Greeter.class",
        "com/newardassociates/demo/Math.class",
        "com/newardassociates/demo/Outer.class",
        "com/newardassociates/demo/Outer\$Inner.class",
        "com/newardassociates/demo/StringConcat.class",
        "com/newardassociates/demo/Varargs.class",
    )
    dependsOn("compileJava")
}

@TaskAction definitely is the magic to make Gradle invoke the task
@Internal is required on the properties inside the task--Gradle apparently really wants to know whether it's an input, output, or internal property. I still need to figure out input and output properties on a custom task.
I think group and description are inherited from DefaultTask, so I should probably figure out how to pass those in a constructor or something
There's probably a better way of dealing with multiple files, but this was sufficient for the Bytecode demos project.
I should probably move those "println" statements over to use the logger instead

Custom Task compiled as part of the build

Custom Task in a standalone JAR

Boilerplates

android-gradle-template - Template project for developing Android app.
vertx-gradle-template - Template project for developing Vert.x module.
gradle-plugin-starter - Template project for developing Gradle plugin.
gatling-with-gradle - Sample project that demonstrates how to automate load testing with Gatling.

Resources

Tags: tool jvm android build

Last modified 28 April 2025