Run JavaExec task in background and then terminate when build completes - jetty

Question

I'm trying to figure out how to launch a JavaExec task that spawns a Jetty server without blocking subsequent tasks. Also, I will need to terminate this server after the build completes. Any idea how I can do this?

Answer 1

I know the thread is from 2011, but I still stumbled across the problem. So here's a solution working with Gradle 2.14:
import java.util.concurrent.Callable
import java.util.concurrent.ExecutorService
import java.util.concurrent.Executors
class RunAsyncTask extends DefaultTask {
String taskToExecute = '<YourTask>'
#TaskAction
def startAsync() {
ExecutorService es = Executors.newSingleThreadExecutor()
es.submit({taskToExecute.execute()} as Callable)
}
}
task runRegistry(type: RunAsyncTask, dependsOn: build){
taskToExecute = '<NameOfYourTaskHere>'
}

Answer 2

I updated solution from #chrishuen because you cannot call execute on task anymore. Here is my working build.gradle
import java.time.LocalDateTime
import java.util.concurrent.Callable
import java.util.concurrent.ExecutorService
import java.util.concurrent.Executors
group 'sk.bsmk'
version '1.0-SNAPSHOT'
apply plugin: 'java'
task wrapper(type: Wrapper) {
gradleVersion = '3.4'
}
class RunAsyncTask extends DefaultTask {
#TaskAction
def startAsync() {
ExecutorService es = Executors.newSingleThreadExecutor()
es.submit({
project.javaexec {
classpath = project.sourceSets.main.runtimeClasspath
main = "Main"
}
} as Callable)
}
}
task helloAsync(type: RunAsyncTask, dependsOn: compileJava) {
doLast {
println LocalDateTime.now().toString() + 'sleeping'
sleep(2 * 1000)
}
}

Answer 3

Hope this snippet will give you some insight on how it can be done.
You can used build listener closures to run code on build start/finish. However, for some reason, gradle.buildStarted closure does not work in milestone-3, so I have replaced it with gradle.taskGraph.whenReady which does the trick.
Then you can call the runJetty task using Task#execute() (Note, this API is not official and may disappear), and additionally, run it from an ExecutorService to get some asynchronous behaviour.
import java.util.concurrent.*
task myTask << {
println "Do usual tasks here"
}
task runJetty << {
print "Pretend we are running Jetty ..."
while(!stopJetty){
Thread.sleep(100)
}
println "Jetty Stopped."
}
stopJetty = false
es = Executors.newSingleThreadExecutor()
jettyFuture = null
//gradle.buildStarted { ... }
gradle.taskGraph.whenReady { g ->
jettyFuture = es.submit({ runJetty.execute() } as Callable)
}
gradle.buildFinished {
println "Stopping Jetty ... "
stopJetty = true
//This is optional. Could be useful when debugging.
try{
jettyFuture?.get()
}catch(ExecutionException e){
println "Error during Jetty execution: "
e.printStackTrace()
}
}

Answer 4

You can't do it with JavaExec; you'll have to write your own task.

Answer 5

Based on previous answers, here is my take:
abstract class RunAsyncTask extends DefaultTask {
#Input
abstract Property<FileCollection> getClasspath()
#Input
abstract Property<String> getMain()
#Input
abstract ListProperty<String> getArgs()
#TaskAction
def startAsync() {
// do get all the parameters before going asynch, otherwise it sometimes blocks
def cp = classpath.get().asPath
def m = main.get()
def a = args.get()
ExecutorService es = Executors.newSingleThreadExecutor()
es.submit({
def command = ["java", "-cp", cp, m] + a
ProcessBuilder builder = new ProcessBuilder(command.toList())
builder.redirectErrorStream(true)
builder.directory(project.projectDir)
Process process = builder.start()
InputStream stdout = process.getInputStream()
BufferedReader reader = new BufferedReader(new InputStreamReader(stdout))
def line
while ((line = reader.readLine()) != null) {
println line
}
} as Callable)
}
}
task startServer(type: RunAsyncTask) {
classpath = ...
main = '...'
args = [...]
doLast {
// sleep 3 seconds to give the server time to startup
Thread.sleep(3000)
}
}