fix(hermetic-build): obtain gapic-generator-java locally on release branch

library_generation/README.md

@@ -72,8 +72,8 @@ You can find the released version of gapic-generator-java in [maven central](htt
 
 Use `--gapic_generator_version` to specify the value.
 
-Note that you can specify a `SNAPSHOT` version as long as you have build the SNAPSHOT of gapic-generator-java in your maven
-local repository.
+Note that you can specify any non-published version (e.g. a SNAPSHOT) as long as you have installed it in your maven
+local repository. The script will search locally first.
 
 ### protobuf_version (optional)
 You can find the released version of protobuf in [GitHub](https://github.com/protocolbuffers/protobuf/releases/).

library_generation/utilities.sh

@@ -75,19 +75,7 @@ remove_grpc_version() {
 
 download_gapic_generator_pom_parent() {
   local gapic_generator_version=$1
-  if [ ! -f "gapic-generator-java-pom-parent-${gapic_generator_version}.pom" ]; then
-    if [[ "${gapic_generator_version}" == *"-SNAPSHOT" ]]; then
-      # copy a SNAPSHOT version from maven local repository.
-      copy_from "$HOME/.m2/repository/com/google/api/gapic-generator-java-pom-parent/${gapic_generator_version}/gapic-generator-java-pom-parent-${gapic_generator_version}.pom" \
-      "gapic-generator-java-pom-parent-${gapic_generator_version}.pom"
-      return
-    fi
-    # download gapic-generator-java-pom-parent from Google maven central mirror.
-    download_from \
-    "https://maven-central.storage-download.googleapis.com/maven2/com/google/api/gapic-generator-java-pom-parent/${gapic_generator_version}/gapic-generator-java-pom-parent-${gapic_generator_version}.pom" \
-    "gapic-generator-java-pom-parent-${gapic_generator_version}.pom"
-  fi
-  # file exists, do not need to download again.
+  download_generator_artifact "${gapic_generator_version}" "gapic-generator-java-pom-parent-${gapic_generator_version}.pom" "gapic-generator-java-pom-parent"
 }
 
 get_grpc_version() {
@@ -114,25 +102,28 @@ download_tools() {
   local protobuf_version=$2
   local grpc_version=$3
   local os_architecture=$4
-  download_generator "${gapic_generator_version}"
+  download_generator_artifact "${gapic_generator_version}" "gapic-generator-java-${gapic_generator_version}.jar"
   download_protobuf "${protobuf_version}" "${os_architecture}"
   download_grpc_plugin "${grpc_version}" "${os_architecture}"
   popd
 }
 
-download_generator() {
+download_generator_artifact() {
   local gapic_generator_version=$1
+  local artifact=$2
+  local project=${3:-"gapic-generator-java"}
   if [ ! -f "gapic-generator-java-${gapic_generator_version}.jar" ]; then
-    if [[ "${gapic_generator_version}" == *"-SNAPSHOT" ]]; then
-      # copy a SNAPSHOT version from maven local repository.
-      copy_from "$HOME/.m2/repository/com/google/api/gapic-generator-java/${gapic_generator_version}/gapic-generator-java-${gapic_generator_version}.jar" \
-      "gapic-generator-java-${gapic_generator_version}.jar"
-      return
+    # first, try to fetch the generator locally
+    local not_found_locally=$(copy_from "$HOME/.m2/repository/com/google/api/${project}/${gapic_generator_version}/${artifact}" \
+      "${artifact}")
+    if [[ "${not_found_locally}" == "true" ]];then 
+      # download gapic-generator-java artifact from Google maven central mirror if not
+      # found locally
+      echo "${artifact} not found locally. Attempting a download from Maven Central"
+      download_from \
+      "https://maven-central.storage-download.googleapis.com/maven2/com/google/api/${project}/${gapic_generator_version}/${artifact}" \
+      "${artifact}"
     fi
-    # download gapic-generator-java from Google maven central mirror.
-    download_from \
-    "https://maven-central.storage-download.googleapis.com/maven2/com/google/api/gapic-generator-java/${gapic_generator_version}/gapic-generator-java-${gapic_generator_version}.jar" \
-    "gapic-generator-java-${gapic_generator_version}.jar"
   fi
 }
 
@@ -174,17 +165,18 @@ download_from() {
   curl -LJ -o "${save_as}" --fail -m 30 --retry 2 "$url" || download_fail "${save_as}" "${repo}"
 }
 
+# copies the specified file in $1 to $2
+# will print "true" if $1 (local_repo) points to a non-existent file
 copy_from() {
   local local_repo=$1
   local save_as=$2
-  cp "${local_repo}" "${save_as}" || \
-    download_fail "${save_as}" "maven local"
+  cp "${local_repo}" "${save_as}" && echo "false" || echo "true"
 }
 
 download_fail() {
   local artifact=$1
   local repo=${2:-"maven central mirror"}
-  >&2 echo "Fail to download ${artifact} from ${repo} repository. Please install ${artifact} first if you want to download a SNAPSHOT."
+  >&2 echo "Fail to download ${artifact} from ${repo} repository. Please install ${artifact} first if you want to use a non-published artifact."
   exit 1
 }