diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index df8824a..491c722 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -9,6 +9,8 @@ jobs:
       min_version: 2.5
   test:
     needs: ruby-versions
+    env:
+      JRUBY_OPTS: '--debug'
     name: build (${{ matrix.ruby }} / ${{ matrix.os }})
     strategy:
       fail-fast: false
@@ -30,6 +32,15 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
+    - name: set up java 21
+      if: ${{ matrix.ruby == 'jruby-head' || matrix.ruby == 'truffleruby' || matrix.ruby == 'truffleruby-head' }}
+      uses: actions/setup-java@v3
+      with:
+        distribution: 'temurin'
+        java-version: 21
+    - name: remove default java except 21
+      if: ${{ matrix.ruby == 'jruby-head' }}
+      run: sudo apt remove temurin-8-jdk temurin-11-jdk temurin-17-jdk
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
diff --git a/Rakefile b/Rakefile
index 9262a89..9407f5b 100644
--- a/Rakefile
+++ b/Rakefile
@@ -3,8 +3,7 @@ require "rake/testtask"
 
 require 'rake/javaextensiontask'
 Rake::JavaExtensionTask.new("escape") do |ext|
-  ext.source_version = '1.8'
-  ext.target_version = '1.8'
+  ext.release = '8'
   ext.ext_dir = 'ext/java'
   ext.lib_dir = 'lib/cgi'