Log failure reason in TensorFlow.init()

tensorflow/java/src/main/java/org/tensorflow/TensorFlow.java

@@ -63,7 +63,19 @@ public final class TensorFlow {
 
   /** Load the TensorFlow runtime C library. */
   static void init() {
-    NativeLibrary.load();
+    try {
+      NativeLibrary.load();
+    } catch (Exception e) {
+      /*
+       * This code is called during static initialization of this and of other classes.
+       * If this fails then a NoClassDefFoundError is thrown however this does not
+       * include a cause. Printing the exception manually here ensures that the
+       * necessary information to fix the problem is available.
+       */
+      System.err.println("Failed to load TensorFlow native library");
+      e.printStackTrace();
+      throw e;
+    }
   }
 
   static {