8281001: Class::forName(String) defaults to system class loader if the caller is null

Reviewed-by: mchung

src/java.base/share/classes/java/lang/Class.java

@@ -357,6 +357,11 @@ public final class Class<T> implements java.io.Serializable,
      * A call to {@code forName("X")} causes the class named
      * {@code X} to be initialized.
      *
+     * <p>
+     * In cases where this method is called from a context where there is no
+     * caller frame on the stack (e.g. when called directly from a JNI
+     * attached thread), the system class loader is used.
+     *
      * @param      className   the fully qualified name of the desired class.
      * @return     the {@code Class} object for the class with the
      *             specified name.
@@ -380,7 +385,9 @@ public final class Class<T> implements java.io.Serializable,
     @CallerSensitiveAdapter
     private static Class<?> forName(String className, Class<?> caller)
             throws ClassNotFoundException {
-        return forName0(className, true, ClassLoader.getClassLoader(caller), caller);
+        ClassLoader loader = (caller == null) ? ClassLoader.getSystemClassLoader()
+                                              : ClassLoader.getClassLoader(caller);
+        return forName0(className, true, loader, caller);
     }
 
     /**

test/jdk/jni/nullCaller/CallHelper.hpp

@@ -24,12 +24,12 @@
 #define __CallHelper_hpp__
 
 #include <stdlib.h>
-#include <stdio.h>
 #include <jni.h>
 #undef NDEBUG
 #include <assert.h>
 #include <string>
 #include <algorithm>
+#include <iostream>
 
 /*
  * basis of classes to provide a bunch of checking in native calls to java
@@ -48,7 +48,7 @@ protected:
     void emitErrorMessage(const std::string& msg) {
         std::string nm = classname;
         std::replace(nm.begin(), nm.end(), '/', '.');
-        ::printf("ERROR: %s::%s, %s\n", nm.c_str(), method.c_str(), msg.c_str());
+        std::cerr << "ERROR: " << nm << "::" << method << ", " << msg << std::endl;
     }
 
     // check the given object which is expected to be null
@@ -202,7 +202,7 @@ public:
 };
 
 void emitErrorMessageAndExit(const std::string& msg) {
-    ::printf("ERROR: %s\n", msg.c_str());
+    std::cerr << "ERROR: " << msg << std::endl;
     ::exit(-1);
 }
 

test/jdk/jni/nullCaller/NullCallerTest.java

@@ -24,7 +24,7 @@
 
 /**
  * @test
- * @bug 8280902 8281000 8281003 8281006
+ * @bug 8280902 8281000 8281003 8281006 8281001
  * @summary Test uses custom launcher that starts VM using JNI that verifies
  *          various API called with a null caller class function properly.
  * @library /test/lib

test/jdk/jni/nullCaller/exeNullCallerTest.cpp

@@ -83,12 +83,10 @@ void registerAsParallelCapable(JNIEnv* env) {
  * Class exp = Class.forName("open.OpenResources");
  */
 void forName(JNIEnv* env) {
-/* coming soon
     StaticCall m_Class_forName { env,
         "java/lang/Class", "forName", "(Ljava/lang/String;)Ljava/lang/Class;" };
 
     m_Class_forName.callReturnNotNull(env->NewStringUTF("open.OpenResources"));
-*/
 }
 
 /*