Fix Java 21 version detection for JreCompat

apache · Feb 21, 2025 · 9e16797 · 9e16797
1 parent 1644abd
commit 9e16797
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/java/org/apache/tomcat/util/compat/Jre21Compat.java b/java/org/apache/tomcat/util/compat/Jre21Compat.java
@@ -32,6 +32,7 @@ public class Jre21Compat extends Jre19Compat {
     private static final Log log = LogFactory.getLog(Jre21Compat.class);
     private static final StringManager sm = StringManager.getManager(Jre21Compat.class);
 
+    private static final boolean supported;
     private static final Method nameMethod;
     private static final Method startMethod;
     private static final Method ofVirtualMethod;
@@ -46,9 +47,14 @@ public class Jre21Compat extends Jre19Compat {
         Method m4 = null;
 
         try {
-            c1 = Class.forName("java.lang.Thread$Builder");
-            m1 = c1.getMethod("name", String.class, long.class);
-            m2 = c1.getMethod("start", Runnable.class);
+            // Note: Virtual threads is the main new feature in Java 21, but it was previously
+            // present as a preview. As a result, it is more accurate to test for another
+            // new class
+            c1 = Class.forName("java.util.SequencedCollection");
+
+            Class<?> c2 = Class.forName("java.lang.Thread$Builder");
+            m1 = c2.getMethod("name", String.class, long.class);
+            m2 = c2.getMethod("start", Runnable.class);
             m3 = Thread.class.getMethod("ofVirtual", (Class<?>[]) null);
             m4 = Subject.class.getMethod("callAs", Subject.class, Callable.class);
         } catch (ClassNotFoundException e) {
@@ -58,14 +64,15 @@ public class Jre21Compat extends Jre19Compat {
             // Should never happen
             log.error(sm.getString("jre21Compat.unexpected"), e);
         }
+        supported = (c1 != null);
         nameMethod = m1;
         startMethod = m2;
         ofVirtualMethod = m3;
         callAsMethod = m4;
     }
 
     static boolean isSupported() {
-        return ofVirtualMethod != null;
+        return supported;
     }
 
     @Override

diff --git a/webapps/docs/changelog.xml b/webapps/docs/changelog.xml
@@ -129,6 +129,10 @@
         Improve the checks for exposure to and protection against CVE-2024-56337
         so that reflection is not used unless required. (markt)
       </fix>
+      <fix>
+        Fix a bug in the JRE compatibility detection that incorrectly identified
+        Java 19 and Java 20 as supporting Java 21 features. (markt)
+      </fix>
     </changelog>
   </subsection>
   <subsection name="Coyote">