diff --git a/.kokoro/common.sh b/.kokoro/common.sh
index ee6770a9d6e1..e1744f9b8b59 100644
--- a/.kokoro/common.sh
+++ b/.kokoro/common.sh
@@ -90,6 +90,9 @@ function retry_with_backoff {
 # and naturally survives single-module components without throwing exit signals.
 function extract_pom_modules() {
   local pom_file="$1"
+  if [[ ! -f "${pom_file}" ]]; then
+    return 1
+  fi
   local modules_list=""
   local in_profiles=false
   local in_modules=false
@@ -109,9 +112,8 @@ function extract_pom_modules() {
       local module="${line#*<module>}"
       module="${module%</module>*}"
       
-      # Trim whitespace natively
-      module="${module#"${module%%[![:space:]]*}"}"
-      module="${module%"${module##*[![:space:]]}"}"
+      # Trim leading/trailing whitespace without spawning external processes
+      read -r module <<< "${module}"
       
       if [ -z "$modules_list" ]; then
         modules_list="$module"
@@ -282,39 +284,48 @@ function generate_modified_modules_list() {
   files=$(get_modified_files)
   printf "Modified files:\n%s\n" "${files}"
 
-  # Generate the list of valid maven modules
-  maven_modules_list=$(mvn help:evaluate -Dexpression=project.modules | grep '<.*>.*</.*>' | sed -e 's/<.*>\(.*\)<\/.*>/\1/g')
+  # Extract valid maven modules directly from pom.xml in pure Bash (~0.02s).
+  # This replaces 'mvn help:evaluate -Dexpression=project.modules' which previously
+  # spent 20-30+ seconds booting a JVM and evaluating the monorepo POMs on every run.
+  local maven_modules_list
+  maven_modules_list=$(extract_pom_modules pom.xml)
   maven_modules=()
 
-  # If the first argument is "true" (default), then use the module exclusion list
-  use_exclusion_list=${1:-true}
+  # Positional parameter $1 specifies whether to apply the exclusion list (defaults to true).
+  local use_exclusion_list="${1:-true}"
+  local module
   if [[ "${use_exclusion_list}" == "true" ]]; then
     echo "Excluding modules from the global exclusion list"
-    for module in $maven_modules_list; do
+    for module in ${maven_modules_list}; do
       if [[ ! " ${excluded_modules[*]} " =~ " ${module} " ]]; then
         maven_modules+=("${module}")
       fi
     done
   else
-    maven_modules=(${maven_modules_list[*]})
+    # 'read -r -a ARRAY <<< STRING' parses a space-delimited string into a Bash array.
+    read -r -a maven_modules <<< "${maven_modules_list}"
   fi
 
   modified_module_list=()
   # If either parent pom.xml or core shared dependency is touched, run ITs on all the modules
   if should_test_all_modules; then
-    modified_module_list=(${maven_modules[*]})
+    # '("${maven_modules[@]}")' copies the array elements safely.
+    modified_module_list=("${maven_modules[@]}")
     echo "Testing the entire monorepo"
   else
-    modules=$(echo "${files}" | grep -E '(google-auth|java)-.*' || true)
+    # Extract the top-level directory from each modified file path:
+    # 'cut -d '/' -f1' takes the first path segment (e.g. 'java-bigquery/src/...' -> 'java-bigquery').
+    # 'sort -u' sorts and deduplicates the candidate directory names.
+    local modules
+    modules=$(cut -d '/' -f1 <<< "${files}" | sort -u)
     printf "Files in java modules:\n%s\n" "${modules}"
-    if [[ -n $modules ]]; then
-      modules=$(echo "${modules}" | cut -d '/' -f1 | sort -u)
-      for module in $modules; do
-        if [[ " ${maven_modules[*]} " =~ " ${module} " ]]; then
-          modified_module_list+=("${module}")
-        fi
-      done
-    else
+    for module in ${modules}; do
+      # If this top-level directory is a recognized Maven module, add it to our list.
+      if [[ " ${maven_modules[*]} " =~ " ${module} " ]]; then
+        modified_module_list+=("${module}")
+      fi
+    done
+    if [[ ${#modified_module_list[@]} -eq 0 ]]; then
       echo "Found no changes in the java modules"
     fi
   fi
diff --git a/.kokoro/common_test.sh b/.kokoro/common_test.sh
index 247a6a26cbfc..bc1b5368cb35 100755
--- a/.kokoro/common_test.sh
+++ b/.kokoro/common_test.sh
@@ -81,6 +81,35 @@ function test_parse_pom_version {
   popd
 }
 
+# Test that extract_pom_modules correctly extracts modules from root pom.xml
+# in pure Bash without launching Maven, and handles non-existent files safely.
+function test_extract_pom_modules {
+  local -a modules
+  read -r -a modules <<< "$(extract_pom_modules "${scriptDir}/../pom.xml")"
+  if (( ${#modules[@]} < 200 )); then
+    echo "extract_pom_modules failed: expected at least 200 modules, got ${#modules[@]}"
+    exit 1
+  fi
+  if [[ ! " ${modules[*]} " =~ " java-bigquery " ]]; then
+    echo "extract_pom_modules missing java-bigquery"
+    exit 1
+  fi
+  if [[ ! " ${modules[*]} " =~ " java-bigquerystorage " ]]; then
+    echo "extract_pom_modules missing java-bigquerystorage"
+    exit 1
+  fi
+  if [[ ! " ${modules[*]} " =~ " sdk-platform-java " ]]; then
+    echo "extract_pom_modules missing sdk-platform-java"
+    exit 1
+  fi
+
+  # Verify non-existent file returns 1 and empty output
+  if extract_pom_modules "non_existent_pom.xml" &>/dev/null; then
+    echo "extract_pom_modules should return non-zero for non-existent pom"
+    exit 1
+  fi
+}
+
 # Tests that is_module_modified strictly matches the module directory prefix,
 # preventing prefix collisions (e.g. java-bigquery vs java-bigquerystorage).
 function test_is_module_modified {
@@ -191,10 +220,51 @@ function test_mock_get_modified_files {
   unset TEST_MODIFIED_FILES
 }
 
+# Test that generate_modified_modules_list correctly maps modified files to
+# their top-level module names without requiring mvn help:evaluate.
+function test_generate_modified_modules_list {
+  pushd "${scriptDir}/.." >/dev/null
+  TEST_MODIFIED_FILES="java-bigquery/google-cloud-bigquery/src/main/java/Foo.java
+sdk-platform-java/gax-java/pom.xml"
+  generate_modified_modules_list false >/dev/null
+
+  local has_bigquery="false"
+  local has_sdk_platform="false"
+  local has_bigquerystorage="false"
+
+  if [[ " ${modified_module_list[*]} " =~ " java-bigquery " ]]; then
+    has_bigquery="true"
+  fi
+  if [[ " ${modified_module_list[*]} " =~ " sdk-platform-java " ]]; then
+    has_sdk_platform="true"
+  fi
+  if [[ " ${modified_module_list[*]} " =~ " java-bigquerystorage " ]]; then
+    has_bigquerystorage="true"
+  fi
+
+  popd >/dev/null
+  unset TEST_MODIFIED_FILES
+
+  if [[ "${has_bigquery}" != "true" ]]; then
+    echo "generate_modified_modules_list missing java-bigquery"
+    exit 1
+  fi
+  if [[ "${has_sdk_platform}" != "true" ]]; then
+    echo "generate_modified_modules_list missing sdk-platform-java"
+    exit 1
+  fi
+  if [[ "${has_bigquerystorage}" == "true" ]]; then
+    echo "generate_modified_modules_list incorrectly included java-bigquerystorage"
+    exit 1
+  fi
+}
+
 test_find_all_poms_with_versioned_dependency
 test_update_pom_dependency
 test_parse_pom_version
 test_mock_get_modified_files
+test_extract_pom_modules
 test_should_test_all_modules
 test_is_module_modified
+test_generate_modified_modules_list
 
diff --git a/.kokoro/presubmit/downstream-build.sh b/.kokoro/presubmit/downstream-build.sh
index aa6781b1ffee..559ad83b5c6b 100755
--- a/.kokoro/presubmit/downstream-build.sh
+++ b/.kokoro/presubmit/downstream-build.sh
@@ -47,10 +47,21 @@ pushd java-showcase
 modify_shared_config
 popd
 
-# Parse showcase version from the local directory
-pushd java-showcase/gapic-showcase
-SHOWCASE_VERSION=$(mvn help:evaluate -Dexpression=gapic-showcase.version -q -DforceStdout)
-popd
+# Extract the showcase version directly from pom.xml using sed:
+# - 'sed -n': suppresses default line printing so only explicit matches are printed.
+# - 's:...[[:space:]]*\(.*\)[[:space:]]*...:\1:p': captures the version text between the tags,
+#   stripping inner whitespace, and prints ('p') only matching lines.
+# - 'head -n 1': guarantees a single line output if multiple matches exist.
+# - 'xargs': trims any remaining leading or trailing whitespace.
+# This replaces 'mvn help:evaluate' which previously took 15+ seconds to boot Maven.
+SHOWCASE_VERSION=$(sed -n 's:.*<gapic-showcase\.version>[[:space:]]*\(.*\)[[:space:]]*</gapic-showcase\.version>.*:\1:p' java-showcase/gapic-showcase/pom.xml | head -n 1 | xargs)
+
+# Fail fast with a clear error message if the version could not be parsed,
+# preventing malformed curl URLs and ambiguous downstream failures.
+if [[ -z "${SHOWCASE_VERSION}" ]]; then
+  echo "Error: Failed to parse gapic-showcase.version from java-showcase/gapic-showcase/pom.xml" >&2
+  exit 1
+fi
 
 # Start showcase server
 mkdir -p /usr/src/showcase