Modified the FieldSerializer to support classes with non-public no-arg constructors.

Finally we can end the tyranny of exposing dangerous public constructors in the
name of a cheap serialization.

jme3-networking/src/main/java/com/jme3/network/serializing/serializers/FieldSerializer.java

@@ -34,6 +34,7 @@ package com.jme3.network.serializing.serializers;
 import com.jme3.network.serializing.Serializer;
 import com.jme3.network.serializing.SerializerException;
 import java.io.IOException;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.nio.BufferOverflowException;
@@ -47,15 +48,31 @@ import java.util.*;
  */
 public class FieldSerializer extends Serializer {
     private static Map<Class, SavedField[]> savedFields = new HashMap<Class, SavedField[]>();
+    private static Map<Class, Constructor> savedCtors = new HashMap<Class, Constructor>();
 
     protected void checkClass(Class clazz) {
     
         // See if the class has a public no-arg constructor
         try {
-            clazz.getConstructor();
+            savedCtors.put(clazz, clazz.getConstructor());
+            return;
+        } catch( NoSuchMethodException e ) {
+            //throw new RuntimeException( "Registration error: no-argument constructor not found on:" + clazz ); 
+        }
+        
+        // See if it has a non-public no-arg constructor
+        try {
+            Constructor ctor = clazz.getDeclaredConstructor();
+            
+            // Make sure we can call it later.
+            ctor.setAccessible(true);
+             
+            savedCtors.put(clazz, ctor);
+            return;
         } catch( NoSuchMethodException e ) {
-            throw new RuntimeException( "Registration error: no-argument constructor not found on:" + clazz ); 
+        }
-        } 
+        
+        throw new RuntimeException( "Registration error: no-argument constructor not found on:" + clazz );  
     }        
     
     public void initialize(Class clazz) {
@@ -121,7 +138,8 @@ public class FieldSerializer extends Serializer {
 
         T object;
         try {
-            object = c.newInstance();
+            Constructor<T> ctor = (Constructor<T>)savedCtors.get(c);
+            object = ctor.newInstance();
         } catch (Exception e) {
             throw new SerializerException( "Error creating object of type:" + c, e );
         }