Gigu’s blogwEBbLOG

On our trip back to home in UK we stopped for 6 days in Bangkok. It is hard to describe but absolutely fantastic to experience. I got a tons of pictures. 500 of them is in the web album. Take a look.

Bangkok

Gregster and The Gang (family)

Nothing more to add really

Last days in Sydney

Greg

I had more time last weeks and today I decided to catch up on Facebook and on Polish version of it, nasza-klasa.pl. There was also old profile of mine on Linkedin and I wanted to Tweet about it as well. So, after few hours I could say I’ barely touched it. It was a lot of reading, looking, watching and typing. It also sucks me up more and more while I’m doing this. Are social networks evil? I guess I will have to do it more frequently and in shorter time.

Over and out, Greg

I have some time this days and I’m trying to fly some clouds with Google App Engine (GAE), Now when they have released Java support I can try to use Groovy. Today I tried to implement some simple storage using JDO. GAE team supports some of its features via  DataNucleus. DataNucleus is using a post compilation hook to enhance any persistable classes.

Having Groovy in a lib folder of your war (GAE runs your application from this folder) I need to put asm library as well. Latest version of Groovy (1.6.1) has a dependency on asm library in version 2.2.3. On the other hand DataNucleus enhancer has dependency on asm library in version 3.1.

GAE Java SDK is shipped with Ant task for enhancing persistable classes. It also contains Ant macro definition file that makes it simple for usage. Unfortunately this macro includes all libraries from application lib folder. This is causing Enhancer to use asm library in a version that causes it to fail massively.

[enhance] SEVERE: An error occured for ClassEnhancer "ASM" when trying to call the method "org.datanucleus.enhancer.as
m.ASMClassEnhancer" on class "getClassNameForFileName" : org.objectweb.asm.ClassReader.accept(Lorg/objectweb/asm/ClassVi
sitor;I)V

Number of this error messages is as big as the number of classes in my application.

Solution is to exclude asm library from the macro that Google shipped. Easiest way is to edit, or copy to your local application folder and use it there. The line problematic line of code is in classpath element.

<classpath>
          <pathelement path="${appengine.tools.classpath}"/>
          <pathelement path="@{war}/WEB-INF/classes"/>
          <fileset dir="@{war}/WEB-INF/lib" includes="*.jar">
          </fileset>
</classpath>

The easiest way to fix it is to exclude asm library in fileset element, just like this:

<classpath>
          <pathelement path="${appengine.tools.classpath}"/>
          <pathelement path="@{war}/WEB-INF/classes"/>
          <fileset dir="@{war}/WEB-INF/lib" includes="*.jar" excludes="asm*.jar">
          </fileset>
</classpath>

Hope that helps anyone with similar problem.

Cheers, Greg

Album with few pictures from Aquarium visit. Awesome place, I would recommend it for anyone to visit.

Sydney Aquarium

Greg and Family

Today I managed to upload two new set of pictures into Picasa. Family pictures from Sydney and Royal National Park.

Sydney memories 29.03

Royal National Park

Cheers, Greg and Family

Ps. Read further for picture slideshow.

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Today I decided to stop hosting pictures on my own blog. Picasa has a great way of uploading it and make things work out of the box without too much hustle.

Today a set of pictures with Oliwia made at our apartment in Sydney and Darling Harbour.

Sydney and Darling Harbour 07.04.2009

Or get there by clicking Sydney and Darling Harbour 07.04.2009.

Cheers, Greg

Hated by many, loved by others. JavaScript is undeniably one of those troubled languages. The fact that it’s implementation and support is not compatible across different web browser makes it even worse and possibly hated by web developers. I would like to look closer into one of the JavaScript features, prototyping.

Some facts

JavaScript is object oriented language. It is “so much” object oriented that even Functions are first-class objects. It could be a surprise for a programmer (like myself) who used to classical object oriented approach, used in Java or C#.

It means that Functions can have properties, another functions, objects etc. Functions could be use to change state of the object or make calculations. They could also be used to create another Functions based on original.

Classes and Prototypes

Classical object oriented language is using types of object, or classes to describe it. In Prototypes one object is describing other, it is almost comparable to cloning.

To make it easier to understand I’d like to use this example:

1. Using classical approach if I asks someone to make me another Aston Martin, I would be asked to get technical specs for it so it could be build it.
2. Using prototypal approach if I ask for Ferrari I will be asked to bring one so they can look at it and build it.

I can define my object and if I need another copy of it I just use prototype to get the same one. In JavaScript world it also means that once I got a bunch of objects that have the same prototype, if I add new property to it I will be able to use it in all of them.

All objects have one common prototype that is Object prototype. Prototype for functions is Function prototype. One useful object method to determine if some object’s property is its own or inherited from its prototype is hasOwnProperty method.

Few examples

To create new Object in JavaScript we don’t need to describe it, just create it:

var myObject = { fooProperty: ‘some value’, barProperty: 2 };

Now if we would like another copy of it we could type something like this:

var Tmp = function(){};
Tmp.prototype = myObject;
var newObject = new Tmp();

You might wonder why is this necessary, looks messy and is not clear. Simple construction :

var newObject = {};
newObject.prototype = myObject;

should work. The reason that it is not is because in first line you are creating the object. Once it’s created it’s got Object as prototype its prototype. Adding another prototype to it’s chain of prototypes will not automatically make it inherit all the properties of another prototype.

Adding new property to prototype could be done using this contruction:

var newObject = {};
newObject.prototype.foo = “some text”;
newObject.prototype.bar = function(){
// do something
}

Multiple prototypes, chain of prototypes

It is impossible to define multiple prototypes for an object.

var objectA = { foo: ‘blah’ };
var objectB = { bar: ‘blah two’ };

var Tmp = function(){};
Tmp.prototype = objectA;
Tmp.prototype = objectB;
var newObject = Tmp.new();

In here newObject will only inherit properties of a last assign prototype and it would be objectB.

If you want to inherit multiple prototypes you have to get Function to help you.

function A(){
    this.foo = ‘blah’;
};
function B(){
    this.bar = ‘another blah’;
};
B.prototype = new A();
var c = new B();

Little help from jQuery

jQuery has a method that helps us to extend one object with some properties from another. Here how you can use it:

function A(){
   this.foo = ’some text’;
}
var anotherObject = { bar: 2 };
$.extend(A.prototype, anotherObject);

Cheers, Greg

I’m trying to catch up with some pictures. Today a batch of Family pictures from Sydney and Taronga Zoo.

Greg and Family

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Project I’m working on has a lot of JavaScript. We are minimizing JavaScript files during the build and combining them into one file. Problem is when someone checks in some invalid JavaScript into repository that doesn’t minify properly. As a result you can end up with not working JavaScript at all. There is a tool called JSLint. It is created by Douglas Crockford who is also the author of a very good book about JavaScript: “JavaScript: The Good Pars”.

JSLint is a very strict JavaScript verifier. JS files corrected to a JSLint specification could be minified with confidence.

We made the decision that build should brake when JSLint detects invalid JavaScript file, so developer will need to fix it before the code checkin.

Prepare the tool base

As a first step we need to get all the tools that will execute JSLint validation against our codebase. You can grab fulljslint.js from the JSLint home page. There is no executable binary for JSLint, it is just a JavaScript file with set of rules and function to execute verification. Our working environment is Windows we can execute validation using cscript.exe command line tool that Windows has. There is a very useful script created by Jason Diamond that helps to execute JSLint validation. You can get it from from here: jslint.wsf. One last thing is a command line batch file that helps execute this tool. You can name it whatever you would like to. I named it jslint.bat. The content of it looks like this:

@cscript //nologo %~dp0\jslint.wsf %*

I put all those three files into build tree, in tools folder. You can check if all the files are valid and working properly by running this command from command line:

jslint.bat c:\path\to\your\js\file.js

Create a build target

Now that we have all the tools we can create a build target. We are using Nant as a build tool. I created Nant target and called it jslint. It looks like this.

<target name="jslint" description="validates JS files">

    <foreach item="File" property="jsfile">

        <in>

            <items>

                <include name="path\to\scripts\folder\**\*.js" />

            </items>

        </in>

        <do>

            <exec program="jslint.bat" commandline="${jsfile}" />

        </do>

    </foreach>

</target>

There is a lot of stuff that could be turned on/off during validation. If you type jslint.bat without any parameters it will give you a list of possible options. Those could as well be tweaked in the jslint.wsf file.

Hope this helps you as it did for us.

Some says that JSLint might hurt your feelings. I say, bring it on

Gregster