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Adobe Flex: Blog Post

How to Prevent Flex Numeric Nulls From Turning to Zeros in BlazeDS

A workaround for unwanted Flex/Java data conversion


		 Double dbl = new Double(Double.NaN); // We emulate incoming numeric null
System.out.println(dbl); //prints NaN, cause dbl "knows" it came from null
long l = new Long(dbl.longValue(new Double(Double.NaN)));
System.out.println(l); // Oops, prints 0!

Unfortunately, native BlazeDS flex.messaging.io.amf.translator.NumberDecoder falls into this trap. So, what is to be done? Luckily, BlazeDS is an open source product and this class has to be slightly modified

Figure 1 illustrates the changes required to protect null-ability of your Long, Integer, etc values, except Double (we explain what to do with Double-s a bit later):

Modified NumberDecoder class  under Deltawalker

Figure 1. Modified NumberDecoder. Farata modification is on the left, canonical BlazeDS class is on the right.

Now, after you make the changes and compile the class against the rest of the flex-messaging-*** jars you can re-jar your own flex-messaging-core.jar.
Better yer, place this class in the common server folder so that it positively affects classpath of all applications on the server.
From now on, Number.NaN will come as Long null, or Integer null – whatever you decide on the Java side.

It this sounds like to big of a deal to you, keep using Double values and convert Double.NaN to null yourself, when appropriate.


Finally, if you would also like to see Double.NaN automatically converted to null, you will have to substitute one more BlazeDS class – flex.messaging.io.amf.translator.NativeDecoder. Explanation: it’s just so happens that BlazeDS marshalling ignores the NumberDecoder when the source (Number, aka Double) and target (Double) types are the same. Here we come and force BlazeDS to use NumberDecoder with numbers no matter what:

    public class NativeDecoder extends ActionScriptDecoder
{
public Object decodeObject(Object shell, Object encodedObject, Class desiredClass)
{
if ( DecoderFactory.isNumber(desiredClass)){
NumberDecoder numberDecoder = new NumberDecoder();
return numberDecoder.decodeObject(encodedObject, desiredClass);
} else
return encodedObject; // the sole original BlazeDS line
}
}

Source code:
NumberDecoder.java modified by Farata
NativeDecoder.java modified by Farata

I’d like to use this opportunity and invite Flex developers living in Europe to attend our Advanced Flex Master Class in Brussels, Belgium on March 1 and 2, 2010.

More Stories By Victor Rasputnis

Dr. Victor Rasputnis is a Managing Principal of Farata Systems. He's responsible for providing architectural design, implementation management and mentoring to companies migrating to XML Internet technologies. He holds a PhD in computer science from the Moscow Institute of Robotics. You can reach him at [email protected]

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