Hi Oliver,

oh I missed that one. Thanks!

Setting the FieldDescriptors on the target message wasn't the way to
go. Because the FD contains a lot of information specific to the
enclosing type. I solved the issue by using a reflection based
approach which is not that nice but will work in the beginning.

public static <T extends Message> T commandToEvent(Message command,
                        Class<T> clazz) {
                try {
                        Method m = clazz.getMethod("newBuilder");
                        Builder builder = (Builder) m.invoke(null);

                        Map<FieldDescriptor, Object> commandFields = 
command.getAllFields();
                        for(Entry<FieldDescriptor, Object> e : 
commandFields.entrySet()) {
                                // Construct JavaBean setter for property
                                String fieldName = e.getKey().getName();
                                char firstChar = 
Character.toUpperCase(fieldName.charAt(0));
                                String setMethod = 
"set"+firstChar+fieldName.substring(1);              
                                
                                // invoke setter with value from the event 
message
                                Method setter = 
builder.getClass().getMethod(setMethod,
e.getValue().getClass());
                                setter.invoke(builder, e.getValue());
                        }       

                        return (T)builder.build();
                } catch (Exception e) {
                        Throwables.propagate(e);                                
                }               
                return null;
        }

On Wed, Jul 25, 2012 at 1:08 AM, Oliver Jowett <oliver.jow...@gmail.com> wrote:
> On Tue, Jul 24, 2012 at 3:55 PM, Tobias Neef <tob...@gmail.com> wrote:
>
>> I try to convert the Java representation of a protobuf message into another
>> message with the same fields (ordering, names, types). I try to do it the
>> following way but this ends in a java.lang.InstantiationException:
>>
>> public static <T extends GeneratedMessage> T commandToEvent(GeneratedMessage
>> command,
>> Class<T> clazz) {
>> try {
>> Builder builder = clazz.newInstance().newBuilderForType();
>
> Generated message classes don't have a public ctor, so newInstance() will 
> fail.
> Pass the default instance of the message class, not the class itself,
> to identify the message type to build?
>
> Oliver

-- 
You received this message because you are subscribed to the Google Groups 
"Protocol Buffers" group.
To post to this group, send email to protobuf@googlegroups.com.
To unsubscribe from this group, send email to 
protobuf+unsubscr...@googlegroups.com.
For more options, visit this group at 
http://groups.google.com/group/protobuf?hl=en.

Reply via email to