Refactor OpenJDK installation routine

Author: Malax

bin/compile

@@ -13,13 +13,14 @@ source "${BUILDPACK_DIR}/lib/util.sh"
 source "${BUILDPACK_DIR}/lib/common.sh"
 source "${BUILDPACK_DIR}/lib/maven.sh"
 source "${BUILDPACK_DIR}/lib/metrics.sh"
+source "${BUILDPACK_DIR}/lib/openjdk.sh"
 
 metrics::init "${CACHE_DIR}" "java"
 metrics::setup
 
 util::export_env_dir "${ENV_DIR}" "." "JAVA_OPTS|JAVA_TOOL_OPTIONS"
 
-common::install_jdk "${BUILD_DIR}" "${CACHE_DIR}"
+openjdk::install_openjdk_via_jvm_common_buildpack "${BUILD_DIR}" "${BUILDPACK_DIR}"
 
 maven::run_mvn "compile" "${BUILD_DIR}" "${CACHE_DIR}"
 maven::remove_mvn "${BUILD_DIR}" "${CACHE_DIR}"

bin/test-compile

@@ -12,10 +12,11 @@ source "${BUILDPACK_DIR}/lib/output.sh"
 source "${BUILDPACK_DIR}/lib/util.sh"
 source "${BUILDPACK_DIR}/lib/common.sh"
 source "${BUILDPACK_DIR}/lib/maven.sh"
+source "${BUILDPACK_DIR}/lib/openjdk.sh"
 
 util::export_env_dir "${ENV_DIR}" "." "JAVA_OPTS|JAVA_TOOL_OPTIONS"
 
-common::install_jdk "${BUILD_DIR}" "${CACHE_DIR}"
+openjdk::install_openjdk_via_jvm_common_buildpack "${BUILD_DIR}" "${BUILDPACK_DIR}"
 
 cd "${BUILD_DIR}"
 

lib/common.sh

@@ -91,18 +91,3 @@ common::cache_copy() {
 		cp -pr "${from_dir}/${rel_dir}"/. "${to_dir}/${rel_dir}"
 	fi
 }
-
-common::install_jdk() {
-	local install_dir="${1}"
-	local cache_dir="${2}"
-
-	JVM_COMMON_BUILDPACK=${JVM_COMMON_BUILDPACK:-https://buildpack-registry.s3.us-east-1.amazonaws.com/buildpacks/heroku/jvm.tgz}
-	mkdir -p /tmp/jvm-common
-	curl --fail --retry 3 --retry-connrefused --connect-timeout 5 --silent --location "${JVM_COMMON_BUILDPACK}" | tar xzm -C /tmp/jvm-common --strip-components=1
-	#shellcheck source=/dev/null
-	source /tmp/jvm-common/bin/java
-	#shellcheck source=/dev/null
-	source /tmp/jvm-common/opt/jdbc.sh
-
-	install_java_with_overlay "${install_dir}" "${cache_dir}"
-}

lib/openjdk.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+openjdk::install_openjdk_via_jvm_common_buildpack() {
+	local build_dir="${1}"
+	# The install_openjdk function from the JVM common buildpack requires the path to the host buildpack to write to the
+	# export script so that OpenJDK can be found by subsequent buildpacks.
+	local host_buildpack_dir="${2}"
+
+	# Legacy behaviour for customers and testing code can override the download location of the heroku/jvm buildpack
+	# with JVM_COMMON_BUILDPACK for testing and debugging purposes.
+	local jvm_common_buildpack_tarball_url="${JVM_COMMON_BUILDPACK:-https://buildpack-registry.s3.us-east-1.amazonaws.com/buildpacks/heroku/jvm.tgz}"
+
+	local jvm_common_buildpack_tarball_path
+	jvm_common_buildpack_tarball_path=$(mktemp)
+
+	local jvm_common_buildpack_dir
+	jvm_common_buildpack_dir=$(mktemp -d)
+
+	curl --silent --fail --retry 3 --retry-connrefused --connect-timeout 5 --location "${jvm_common_buildpack_tarball_url}" -o "${jvm_common_buildpack_tarball_path}"
+	tar -xzm --directory "${jvm_common_buildpack_dir}" --strip-components=1 "${jvm_common_buildpack_tarball_path}"
+
+	# This script translates non-JDBC compliant DATABASE_URL (and similar) environment variables into their
+	# JDBC compatible counterparts and writes them to "JDBC_" prefixed environment variables. We source this script
+	# here to allow customers to connect to their databases via JDBC during the build. If no database environment
+	# variables are present, this script does nothing.
+	# shellcheck source=/dev/null
+	source "${jvm_common_buildpack_dir}/opt/jdbc.sh"
+
+	# shellcheck source=/dev/null
+	source "${jvm_common_buildpack_dir}/bin/java"
+
+	# See: https://github.com/heroku/heroku-buildpack-jvm-common/blob/main/bin/java
+	install_openjdk "${build_dir}" "${host_buildpack_dir}"
+}