Support running Netty in bootstrap class loader

Motivation:

Fix NullPointerExceptions that occur when running netty-tcnative inside the bootstrap class loader.

Modifications:

- Replace loader.getResource(...) with ClassLoader.getSystemResource(...) when loader is null.
- Replace loader.loadClass(...) with Class.forName(..., false, loader) which works when loader is both null and non-null.

Result:

Support running native libs in bootstrap class loader

common/src/main/java/io/netty/util/internal/NativeLibraryLoader.java

@@ -136,13 +136,22 @@ public final class NativeLibraryLoader {
         InputStream in = null;
         OutputStream out = null;
         File tmpFile = null;
-        URL url = loader.getResource(path);
+        URL url;
+        if (loader == null) {
+            url = ClassLoader.getSystemResource(path);
+        } else {
+            url = loader.getResource(path);
+        }
         try {
             if (url == null) {
                 if (PlatformDependent.isOsx()) {
                     String fileName = path.endsWith(".jnilib") ? NATIVE_RESOURCE_HOME + "lib" + name + ".dynlib" :
                             NATIVE_RESOURCE_HOME + "lib" + name + ".jnilib";
-                    url = loader.getResource(fileName);
+                    if (loader == null) {
+                        url = ClassLoader.getSystemResource(fileName);
+                    } else {
+                        url = loader.getResource(fileName);
+                    }
                     if (url == null) {
                         FileNotFoundException fnf = new FileNotFoundException(fileName);
                         ThrowableUtil.addSuppressedAndClear(fnf, suppressed);
@@ -280,8 +289,12 @@ public final class NativeLibraryLoader {
     private static Class<?> tryToLoadClass(final ClassLoader loader, final Class<?> helper)
             throws ClassNotFoundException {
         try {
-            return loader.loadClass(helper.getName());
+            return Class.forName(helper.getName(), false, loader);
         } catch (ClassNotFoundException e1) {
+            if (loader == null) {
+                // cannot defineClass inside bootstrap class loader
+                throw e1;
+            }
             try {
                 // The helper class is NOT found in target ClassLoader, we have to define the helper class.
                 final byte[] classBinary = classToByteArray(helper);

common/src/test/java/io/netty/util/internal/NativeLibraryLoaderTest.java

@@ -17,6 +17,7 @@ package io.netty.util.internal;
 
 import org.junit.Test;
 
+import java.lang.reflect.Method;
 import java.io.FileNotFoundException;
 import java.util.UUID;
 
@@ -25,6 +26,8 @@ import static org.junit.Assert.fail;
 
 public class NativeLibraryLoaderTest {
 
+    private static final Method getSupressedMethod = getGetSuppressed();
+
     @Test
     public void testFileNotFound() {
         try {
@@ -32,6 +35,47 @@ public class NativeLibraryLoaderTest {
             fail();
         } catch (UnsatisfiedLinkError error) {
             assertTrue(error.getCause() instanceof FileNotFoundException);
+            if (getSupressedMethod != null) {
+                verifySuppressedException(error, UnsatisfiedLinkError.class);
+            }
+        }
+    }
+
+    @Test
+    public void testFileNotFoundWithNullClassLoader() {
+        try {
+            NativeLibraryLoader.load(UUID.randomUUID().toString(), null);
+            fail();
+        } catch (UnsatisfiedLinkError error) {
+            assertTrue(error.getCause() instanceof FileNotFoundException);
+            if (getSupressedMethod != null) {
+                verifySuppressedException(error, ClassNotFoundException.class);
+            }
+        }
+    }
+
+    private static void verifySuppressedException(UnsatisfiedLinkError error,
+            Class<?> expectedSuppressedExceptionClass) {
+        try {
+            Throwable[] suppressed = (Throwable[]) getSupressedMethod.invoke(error.getCause());
+            assertTrue(suppressed.length == 1);
+            assertTrue(suppressed[0] instanceof UnsatisfiedLinkError);
+            suppressed = (Throwable[]) getSupressedMethod.invoke(suppressed[0]);
+            assertTrue(suppressed.length == 1);
+            assertTrue(expectedSuppressedExceptionClass.isInstance(suppressed[0]));
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static Method getGetSuppressed() {
+        if (PlatformDependent.javaVersion() < 7) {
+            return null;
+        }
+        try {
+            return Throwable.class.getDeclaredMethod("getSuppressed");
+        } catch (NoSuchMethodException e) {
+            throw new RuntimeException(e);
         }
     }
 }