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Create a gradle build file, call it deps.gradle, as follows:

apply plugin: 'java'

repositories {
   mavenCentral()
}

dependencies {
   compile group: 'org.glassfish.jersey.bundles', name: 'jaxrs-ri', version: '2.23.1'
}

task copyDependencies(type: Copy) {
   from configurations.compile
   into 'dependencies'
}

Then call gradle -b deps.gradle copyDependencies and it'll put all the dependencies into the dependencies/ directory.