Your implementation doesn't handle the case where adding a value to the map
overwrites an existing entry. In that case, you shouldn't add a new entry to
your list of keys, but replace one of them.
When the map is transferred over RPC, the key list is sent with the data. When
RPC reconstitutes the map, it adds key,value pairs one at a time. Unforunately,
since you start with a non-empty list of keys, as it rebuilds the map and calls
put(K,V), it will add a new key each time.
Even if your implementation overcame the above problem, RPC will still send the
keys twice over the wire - once embedded in the map, and once in your list of
keys. So if you really want an implementation like this, you ought to write
your own custom field serializer to make the on-the-wire format more efficient.
You would also be able to control the way the map was reconstituted from its
parts.
OTOH, If you can do without your get(int) method, you could just use a
LinkedHashMap instead. It remembers insertion order.
Paul
On 15/09/11 11:23, Maverick wrote:
I'm having a strange behavior (at least, something that I don't
understand) during derialization/deserialization, which causes values
to be duplicated to a List.
I have a custom Map that basically adds key order preserving through
an ArrayList. Each time a key/value pair is put into the map, the key
is also added to an ArrayList. When a class instance is passed through
a RPC the map is serialized correctly (or at least the data is the
same before and after); but the list seems to be deserialized twice
and two copies of the keys exist after.
In the code below, I instantiate the CustomMap and add the key "10"; I
expect to have one key received on the server and one key sent back to
the client. However, the output is the following:
Before sending: [10]
On server: [10, 10]
Received back: [10, 10, 10]
Am I missing some GWT programming principle?
How could I implement such feature without suffering that problem?
Thanks
Here the code:
/* The custom map; to every put, the key is also added to the list.
*/
public class CustomMap<K, V> extends HashMap<K, V> implements
Serializable, IsSerializable
{
private static final long serialVersionUID =
-1780691944208423396L;
ArrayList<K> list =
new ArrayList<K>();
public CustomMap()
{
}
@Override
public V put( K key, V value )
{
return put( key, value, this.list.size() );
}
public V put( K key, V value, int index )
{
this.list.add( index, key );
return super.put( key, value );
}
public V get( int n )
{
return get( key( n ) );
}
public int indexOf( K key )
{
return this.list.indexOf( key );
}
public K key( int n )
{
return this.list.get( n );
}
public ArrayList<K> getData()
{
return this.list;
}
}
/* The RPC call; just send a CustomMap forth and back
*/
public void onModuleLoad()
{
CustomMap<Long, String> map = new CustomMap<Long, String>();
map.put( new Long( 10 ), "a value" );
System.out.println( "Before sending: " + map.getData() );
service.transfer( map, new AsyncCallback<CustomMap<Long,
String>>(){
@Override
public void onSuccess( CustomMap<Long, String> result )
{
System.out.println( "Received back: " +
result.getData() );
}
@Override
public void onFailure( Throwable caught ) {}
} );
}
/* Server-side code, for completeness
*/
public CustomMap<Long, String> transfer( CustomMap<Long, String>
map )
{
System.out.println( "On server: " + map.getData() );
return map;
}
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