Sunday, August 10, 2008

Modern programming languages provide a mixture of primitives for composing programs. Most notably Scheme, Smaltalk, Ruby, and Scala have direct language support for parameterized delayed-execution blocks of code, variously called lambda, anonymous functions, or closures. These provide a natural way to express some kinds of abstractions that are currently quite awkward to express in Java. For programming in the small, anonymous functions allow one to abstract an algorithm over a piece of code; that is, they allow one to more easily extract the common parts of two almost-identical pieces of code.

Closure Literals

We introduce a syntactic form for constructing an anonymus function value:

{ FormalParametersopt => BlockStatementsopt Expressionopt }

Evaluating the closure literal expression results in a closure instance . A closure instance is converted to some object type by a closure conversion. In the nominal version of the specification, it is a compile-time error if a closure literal appears in a context where it is not subject to a closure conversion. In the functional version of the specification, if a closure literal is not subject to a closure conversion it is converted to the corresponding function type of the closure literal, which is the function type with: identical argument types; a return type that is the type of the final expression, if one exists, or java.lang.Unreachable if the closure literal's body cannot complete normally, or void otherwise; and a throws type list corresponding to the checked exception types that can be thrown from the body of the closure literal. The conversion, in either case, occurs entirely at compile-time.

A closure literal captures a block of code - the block statements and the expression - parameterized by the closure literal's formal parameters. All free lexical bindings - that is, lexical bindings not defined within the closure literal - are bound at the time of evaluation of the closure literal to their meaning in the lexical context in which the closure literal appears. Free lexical bindings include references to variables from enclosing scopes, and the meaning of this, break, continue, and return. Evaluating the closure literal does not cause the statements or expression to be evaluated, but packages them up at runtime with a representation of the lexical context to be invoked later.

At runtime, if a break statement is executed that would transfer control out of a statement that is no longer executing, or is executing in another thread, the VM throws a new unchecked exception, UnmatchedNonlocalTransfer. Similarly, an UnmatchedNonlocalTransfer is thrown when a continue statement attempts to complete a loop iteration that is not executing in the current thread. Finally, an UnmatchedNonlocalTransfer is thrown when a return statement is executed if the method invocation to which the return statement would transfer control is not on the stack of the current thread.


Varun Rathore

Saturday, August 9, 2008

Cairngorm Is Open Source Now

This week Adobe announced that Cairngorm has been moved to from Labs to

So what does this mean for you, as a developer, building RIAs targeting the Adobe Flex platform on top of Cairngorm?

It means a lot.

The most significant being that Cairngorm now has a formal community based initiative. This in itself facilitates positive growth as it encourages community feedback and collaboration. It allows the community to have an open pool for discussion, collaboration and most important, knowledge sharing.

R u willing to contribute?
To begin, start by signing up as a member and sharing your thoughts and experiences. Get involved; engage in conversations with the rest of the community. Take a look under the stage; get to know Cairngorm internals (if you don’t already).

Expect Good Things To Come Now..


Varun Rathore

Friday, August 8, 2008

dpHibernate - Hibernate lazy loading with Adobe BlazeDS

One of the biggest problems with working with data in a RIA/Flex application is that it's all or nothing. You either need to get all of the data or write a lot of code to return the data in multiple requests. The problem is that good design means that we want to design our data object to match the data, not the UI. For instance a User might have an array of Orders which each have an array of Items. Seems simple enough, right. The problem is that this is a large complex objects which could require a query that joins multiple tables when returning data to your application. No big deal if you want to display all of the data. But if you are just trying to output the users name and email in a search result screen then this is a huge performance hit.

Luckily there is a solution, It is called lazy loading. JSP developers, which use the java hibernate framework, have been able to use lazy loading for years. But until now this did not work with remote client applications like Flex. For those of you who have tried, I'm sure your familiar with the dreaded LazyLoadingException. Frustrating huh. Lazy loading let's your define a complete object model, such as a User with an array of Orders. But only return the data you are actually using in your presentation layer (Flex). Avoiding that all or nothing data problem that is so common.

I'm happy to announce a new Digital Primates open source project. dpHibernate, add support to BlazeDS for Hibernate lazy loading. You can find both the java and the ActionScript parts of the project here:
If you're not familiar with hibernate, check out At a real high level, Hibernate is a java ORM tool, which lets you map java beans to a relation database. Hibernate does all of the sql work for you.

So how do dpHibernate work? dpHibernate is actually a combination of two code bases. First, there is a custom java adapter for the BlazeDS server. This HibernateAdapter understands the hibernate proxy objects and knows how to convert them into a special dpHibernate proxy which the AMF serializer will ignore and not try to initialize. This is how the proxy objects are able to go back to the client without getting the LazyLoadingException.

The second part of dpHibernate is an ActionScript library which gives your application the code it needs to understand these dpHibernate proxy objects. This AS library has the code to manage your ActionScript beans and knows how to call back to the server to load a proxy once that object has been touched, usually with a binding expression.

In case your wondering, how does dpHibernate differ from the hibernate support in LiveCycle Data Services ES? For one dpHibernate doesn't require LCDS it works with the open source BlazeDS server. The other big difference is that hibernate support in LCDS requires you to duplicate the lazy associations in the services-config.xml and you need to use an Assembler class to get the hibernate objects. dpHibernate let's you call any java method and return any hibernate object.

So check it out, if you can use it I'd love to hear about it. If it doesn't work for you I want to know about that too. And as with all open source projects this one can use as many eyes as possible on it too. If you find any hibernate configurations that don't work let me know. Or better yet, send me a test case with the right hibernate mapping files to recreate the issue.

Thursday, August 7, 2008

Cool Flex Refresh Component

The HttpRefresher component can refresh data from server-side at specified intervals.

FleXtense - Open Source

FleXtense is an application for Flex Users which composes the automatic ActionScript proxy classes for accessing the web services. It provides to compose rapid and safe codes with its supporting data types and easy to use interface. FleXtense is a platform independent application because it has taken wsdl schema standart which are based from World Wide Web Consortium ( You can use FleXtense with Java, .net, pHp, Ruby etc.

Complete Uninstalling -- AIR Application

Uninstalling and reinstalling the application dont delete the retained my user data. You’ve probably seen similar behavior in some of your AIR applications. The problem is that when you uninstall an AIR application it doesn’t get rid of the encrypted local store data. Here’s the solution.

Basically if you want to completely blow away an AIR app you need to go into the “/Users//Library/Application Support/Adobe/AIR/ELS”, find your application based on the id and then delete the application data.

On Windows it’s “C:\Documents and Settings\\Application Data\Adobe\AIR\ELS” (ELS stands for Encrypted Local Store).


Varun Rathore

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