Access of Jars from Gradle cache

25 September 2020

There are times where you quickly need the path to a JAR-file from the Gradle cache. For Maven this is quiet straight-forward as the path of a file in the local Maven cache (~/.m2/repository) is determined alone by the GAV coordinates. This is not the case for Gradle. Files are located under ~/.gradle/caches but the folder-names look like they are hash-values and the only way I know how to get the path of a JAR-file is by actually running a Gradle build-script that downloads and resolves the dependency.

For this reason, I now have a small shell-script that does it exactly that:

#!/bin/bash
# gradle-resolve.sh
tmp_dir=$(mktemp -d)
cat << EOF > $tmp_dir/build.gradle
plugins {
    id 'java'
}

repositories {
    jcenter()
}

dependencies {
    implementation "$2"
}

tasks.register("getClasspath") {
    doLast {
        println configurations.runtimeClasspath.join(':')
    }
}

tasks.register("getJar") {
    doLast {
        println configurations.runtimeClasspath[0]
    }
}
EOF

(cd $tmp_dir && gradle $1 --console=plain --quiet)

It can be invoked with getJar to get the path of the JAR in the Gradle cache:

gradle-resolve.sh getJar org.jboss:jandex:2.0.5.Final
/home/daniel/.gradle/caches/modules-2/files-2.1/org.jboss/jandex/2.0.5.Final/7060f67764565b9ee9d467e3ed0cb8a9c601b23a/jandex-2.0.5.Final.jar

Or it can be invoked with getClasspath to get the whole runtime-classpath.

gradle-resolve.sh getClasspath org.eclipse.jetty:jetty-server:9.4.29.v20200521
/home/daniel/.gradle/caches/modules-2/files-2.1/org.eclipse.jetty/jetty-server/9.4.29.v20200521/2c6590067589a0730223416c3157b1d4d121b95b/jetty-server-9.4.29.v20200521.jar:/home/daniel/.gradle/caches/modules-2/files-2.1/javax.servlet/javax.servlet-api/3.1.0/3cd63d075497751784b2fa84be59432f4905bf7c/javax.servlet-api-3.1.0.jar:/home/daniel/.gradle/caches/modules-2/files-2.1/org.eclipse.jetty/jetty-http/9.4.29.v20200521/21b761eae53b8e5201fb8fdf03b9865116a29b47/jetty-http-9.4.29.v20200521.jar:/home/daniel/.gradle/caches/modules-2/files-2.1/org.eclipse.jetty/jetty-io/9.4.29.v20200521/ffadd07dc4e9d0783531922ed565b667ad95766e/jetty-io-9.4.29.v20200521.jar:/home/daniel/.gradle/caches/modules-2/files-2.1/org.eclipse.jetty/jetty-util/9.4.29.v20200521/4866aa5271465f1d9035c4726209e4926fe1599c/jetty-util-9.4.29.v20200521.jar

So, to run the Main-Class from the jandex jar, you can execute:

java -jar $(gradle-resolve.sh getJar org.jboss:jandex:2.0.5.Final)