4917309: (cl) Reduce internal usage of ClassNotFoundExceptions during class-loading

Summary: Change findBootstrapClass to return null instead of throwing CNFE if class not found
Reviewed-by: alanb, dholmes, iris

src/share/classes/java/lang/ClassLoader.java

@@ -384,9 +384,14 @@ public abstract class ClassLoader {
                     if (parent != null) {
                         c = parent.loadClass(name, false);
                     } else {
-                        c = findBootstrapClass0(name);
+                        c = findBootstrapClassOrNull(name);
                     }
                 } catch (ClassNotFoundException e) {
+                    // ClassNotFoundException thrown if class not found
+                    // from the non-null parent class loader
+                }
+
+                if (c == null) {
                     // If still not found, then invoke findClass in order
                     // to find the class.
                     c = findClass(name);
@@ -1008,22 +1013,29 @@ public abstract class ClassLoader {
         if (system == null) {
             if (!checkName(name))
                 throw new ClassNotFoundException(name);
-            return findBootstrapClass(name);
+            Class cls = findBootstrapClass(name);
+            if (cls == null) {
+                throw new ClassNotFoundException(name);
+            }
+            return cls;
         }
         return system.loadClass(name);
     }
 
-    private Class findBootstrapClass0(String name)
-        throws ClassNotFoundException
+    /**
+     * Returns a class loaded by the bootstrap class loader;
+     * or return null if not found.
+     */
+    private Class findBootstrapClassOrNull(String name)
     {
         check();
-        if (!checkName(name))
-            throw new ClassNotFoundException(name);
+        if (!checkName(name)) return null;
+
         return findBootstrapClass(name);
     }
 
-    private native Class findBootstrapClass(String name)
-        throws ClassNotFoundException;
+    // return null if not found
+    private native Class findBootstrapClass(String name);
 
     // Check to make sure the class loader has been initialized.
     private void check() {

src/share/javavm/export/jvm.h

@@ -374,6 +374,12 @@ JVM_FindPrimitiveClass(JNIEnv *env, const char *utf);
 JNIEXPORT void JNICALL
 JVM_ResolveClass(JNIEnv *env, jclass cls);
 
+/*
+ * Find a class from a boot class loader. Returns NULL if class not found.
+ */
+JNIEXPORT jclass JNICALL
+JVM_FindClassFromBootLoader(JNIEnv *env, const char *name);
+
 /*
  * Find a class from a given class loader. Throw ClassNotFoundException
  * or NoClassDefFoundError depending on the value of the last

src/share/native/java/lang/ClassLoader.c

@@ -237,6 +237,9 @@ Java_java_lang_ClassLoader_resolveClass0(JNIEnv *env, jobject this,
     JVM_ResolveClass(env, cls);
 }
 
+/*
+ * Returns NULL if class not found.
+ */
 JNIEXPORT jclass JNICALL
 Java_java_lang_ClassLoader_findBootstrapClass(JNIEnv *env, jobject loader,
                                               jstring classname)
@@ -246,7 +249,6 @@ Java_java_lang_ClassLoader_findBootstrapClass(JNIEnv *env, jobject loader,
     char buf[128];
 
     if (classname == NULL) {
-        JNU_ThrowClassNotFoundException(env, 0);
         return 0;
     }
 
@@ -258,11 +260,10 @@ Java_java_lang_ClassLoader_findBootstrapClass(JNIEnv *env, jobject loader,
     VerifyFixClassname(clname);
 
     if (!VerifyClassname(clname, JNI_TRUE)) {  /* expects slashed name */
-        JNU_ThrowClassNotFoundException(env, clname);
         goto done;
     }
 
-    cls = JVM_FindClassFromClassLoader(env, clname, JNI_FALSE, 0, JNI_FALSE);
+    cls = JVM_FindClassFromBootLoader(env, clname);
 
  done:
     if (clname != buf) {