Java and other things

Surprise

2011-04-07T01:39:00.002+10:00

I was washing the dishes after dinner tonight. I was going to put the cuttlery away when I got surprised.

I love you son!

Sokoban

2011-04-07T00:59:00.002+10:00

My wife and I were having dinner tonight. As it usually happens out little son finished quickly and was getting restless. So we put him down from his chair and carried on with our meals. Soon after he pulled his chair from the table and pushed it to the door that leads to our backyard. I kept an eye on him, just like any parents would do with a boy who is always up to something. So he pulled this chair to the door, climbed on top of it and the victoriously stood on it, giving me the biggest smile he could. His eye were saying "Look dad! I did it!"

Then I realized what he was up to. He put his little hand up and tried to reach for the air-conditioning unit above him. Near the ceiling. I was impressed with the little guy’s thinking. He used the same logic we (big guys) would use to reach to places that we naturally cannot reach as our bodies do not extend that far. He just underestimated the distance. He is only two. Almost. I praised him for his effort and I told him that he’s done well and he will get there but it may take a few years until he is big enough.

At that very moment I realized that for these little ones with no limits, no boundaries pre-set in their minds the sky is the true limit.

After I asked him to come down (just to be safe) he started pushing that chair around. He maneuvered with it around the kitchen and eventually made it to the very spot he took this chair from. Sokoban! The only movement my son decided to use was to push the chair. It was fun for him, as well as for me watching him. When he made it do the destination, it dawned on me. He just performed a real-life version of Sokoban. Wow! The kiddo is smart and I wish I was back in 80-ties to re-invent the popular computer game :-)

Don’t limit your kids. Let them explore, invent and make up their own rules for this world they live in.

404! Why? Where from?

2010-09-07T13:00:00.004+10:00

Alright, so you got 404'd! Things aren't that bad because you handled it nicely, but the real question you have on the tip of your tongue is "What URL caused this 404?"

The request could receive the following attributes that can indicate what caused the error

Where did it come from?

To get the original URL of the request that is in trouble, look at javax.servlet.error.request_uri request attribute.

String uri = (String) request.getAttribute("javax.servlet.error.request_uri");

What caused it?

To cause of the error can be a HTTP error or an exception that was not handled by the web application and propagated all the way up. The three attributes that will give you more insight are:

javax.servlet.error.status_code:
An Integer telling the error status code, if any
javax.servlet.error.exception_type:
A Class instance indicating the type of exception that caused the error, if any
javax.servlet.error.message:
A String telling the exception message, passed to the exception constructor
javax.servlet.error.exception:
A Throwable object that is the actual exception thrown

Handling HTTP 404 - Page Not Found

2010-09-07T10:31:00.004+10:00

If you develop web applications, you are most likely familiar with Java Servlets and Java Server Pages (JSP). JSPs can be accessed by a path that directly relates to their relative location to the web app's content root directory. Servlets however are typically accessed via path that match URL patterns defined for each servlet in the servlet mapping element of the deployment descriptor (web.xml).

What happens if a user types in a URL that will reach your web application, but does not map to to any of your servlets nor JSPs? Most likely this occurrence will be handler by the servlet container itself by sending HTTP 404 code back to the user's browser. A 404 page will be displayed. 404 is a HTTP response status code that indicates that a resource could not be found but may be available again in the future. Most of the servlet containers do not serve user-friendly 404 pages.

You are better off handling 404 by the web application itself. The content of the 404 page can be then customized to suit your web application's needs. You could take a funny approach or present something more helpful, e.g. a sitemap.

Example from YOU & I tee - couple t-shirts:

So how do we do this?

Step 1 - Create error page description

Add an error-page element to your web applications deployment descriptor. Open web.xml file and add a section like the following:

<error-page>
 <error-code>404</error-code>
 <location>/error404.jsp</location>
</error-page>

Step 2 - Create error JSP

At the location as specified in step 1 create a new JSP file that will serve the content you desire. And that's it really.

Handling exceptions

In a similar fashion you can handle uncaught exceptions that would otherwise end up in the user's browser. For example:

<error-page>
 <exception-type>java.lang.RuntimeException</exception-type>
 <location>/exception.jsp</location>
</error-page>

JavaZone Trailer: Java 4-ever

2010-06-27T02:22:00.003+10:00

This is an absolutely awesome movie trailer!

...from the director of JAVATAR and .NOT

How to wire a constant in Spring

2010-05-03T13:40:00.005+10:00

Spring is a great framework for dependency injection. It helps creating new instances and inject them with references to other objects via constructor arguments or setter methods.

To create a new instance of a class one simply declares a new bean

<bean id="firstDay" class="com.mypackage.Day">
    <constructor-arg type="java.lang.Integer" value="1" />
</bean>

But what if you do not want to create a new instance. Perhaps you already have a class with instances declared as publicly accessible constants (public static) and you just want to access them in the wiring process.

It's easy to get a hold of a constant. Simply use the following

<util:constant id="firstDay" static-field="com.mypackage.Day.MONDAY"/>

For this to work you'll need to include the following

<beans
    xmlns="http://www.springframework.org/schema/beans"
    ...
    xmlns:util="http://www.springframework.org/schema/util"
    xsi:schemaLocation="http://www.springframework.org/schema/util ..."
>

So there you go, now you have constants wired.

Xmas Party 2009

2010-01-08T01:13:00.003+11:00

HotHouse had a great Christmas party at Peats Bite restaurant last year.

See the rest of the photos in my photo set.

jQuery and checkboxes

2009-09-03T22:52:00.002+10:00

Let's start with a simple checkbox like this:

<input type="checkbox" name="foo" value="bar" />

To check whether this checkbox is checked you can do either of the following two alternatives:

$('input[name=foo]').is(':checked')
$('input[name=foo]').attr('checked')

To check the checkbox we can use the attr() function

$('input[name=foo]').attr('checked', true);

And likewise to uncheck it

$('input[name=foo]').attr('checked', false);

Leveraging Google to build your business

2009-07-31T11:15:00.004+10:00

I read a nice post this morning about building business with Google by Eric at 過労死 Death by Overcoding.

It covers many aspects that may be involved in administering your business needs, such as:

Domain registration/host/email/office apps
Phone Management
Blog
The Application
Payments
AdWords
Analytics
Integration/Optimization

I recommend reading it to anyone who is starting up a web business. Following the steps mentioned in that blog post can be a real timesaver. And you do not need to hire an admin to do it all.

Detect an AJAX request

2009-07-30T17:02:00.005+10:00

Many web applications use AJAX nowadays. In a typical scenario, one fills out a form, which is then submitted to the server. If you don't use AJAX or JavaScript is disabled, your form should still submit with no problems. And you receive a new page. If you use unobtrusive enhancement via JavaScript, the form is submitted to the server and the page is updated with the result without a full page reload.

While developing with Grails writing Java and Groovy code, I noticed that a typical pattern is to create two actions in a controller. One to handle normal HTTP POST (e.g. save action) and one to handle HTTP POST coming from an AJAX request (e.g. saveAjax action). The two actions are almost identical. They perform the same business logic. The only difference is what is returned from each action. A normal action renders a new page. An AJAX one returns whatever your flavor is: XML, JSON, HTML, plain text.

So is there a way to tell the requests (ordinary and AJAX) apart?

You guessed it, there is. AJAX request comes with a special header - X-Requested-With. I usually have my controllers to extend my BaseController, which has a couple of useful methods that I use. isAjax(request) is one of them. And this is what it looks like.


public static boolean isAjax(request) {
   return "XMLHttpRequest".equals(request.getHeader("X-Requested-With"));
}

I hope you'll find it useful. The all you need to do in your action is this:


def save = {

    // business logic
    // ...

    if (isAjax(request)) {
        render([ /* data */ ] as JSON)
    }
    else {
        // render or redirect here
        render(view: 'save', model: [ /* model data */ ])
    }
}

Grails.org has a new home page design

2009-07-30T16:35:00.004+10:00

I absolutely love the new design of the grails.org home page. It's sleek, clean, easy to find what you need. Simply brilliant!

Visual Event

2009-03-13T10:03:00.003+11:00

This is a really neat tool by Allan Jardine, a UI developer! It makes it so easy and visual to see what even handlers are attached to the elements of a page. Great addition to my toolbox!

When working with events in Javascript, it is often easy to loose track of what events are subscribed where. This is particularly true if you are using a large number of events, which is typical in a modern interface employing progressive enhancement. Javascript libraries also add another degree of complexity to listeners from a technical point of view, while from a developers point of view they of course can make life much easier! But when things go wrong it can be difficult to trace down why this might be.

Read the whole article about Visual Event

jQuery 1.3 upgrade & selector bug

2009-01-18T00:59:00.003+11:00

I've just upgraded my website to jQuery 1.3. First thing that broke was the attribute selector. This was well documented in the jQuery 1.3 Release Notes - Upgrading as well as in the documentation. So this was easily fixed.

Another problem I had was with a selector matching <select> tags, such as

$('.size select')

For some reason it is no longer matching the <select> tag, but it's <option> tags instead. There is plenty of buzz about how jQuery switched to Sizzle.js selector engine and all the performance gains. I have not found any information pointing to the change that causes by selector bug. Navigating to the parent node solved the issue for me, but it's more like an ugly hack rather than expected behavior.

$('.size select').parent()

Anybody else noticed this problem?

Tagline

2009-01-03T23:24:00.003+11:00

It has been quite a few busy weeks since my last post. I was heavily snowed down with work on my website. Then there was Christmas and new years celebrations.

Happy new year, everybody! On the optimistic note:

Let the new year be better than it is going to be!

:-)

What am I doing right now?

I am thinking about a tag line for my new website. The site will be selling special t-shirts for couples. These t-shirts will have funny designs split 50:50. So the big question is what should the tag line say?

Couple of my (pretty bad) ideas:

Couple T-Shirts ...because one is not complete
Couple T-Shirts two is better than one
Couple T-Shirts one for you, one for your +1

I would like to hear your suggestions.

Colors for the web

2008-12-05T16:06:00.003+11:00

Do you need to find interesting photos that would enhance your website and would perfectly match its color scheme? I found a perfect tool for that job.

Multicolr Search Lab by Idée Inc.

And these are the images that match colors of my blog:

orange

orange & blue

blue

Easy Groovy Iteration

2008-12-05T15:17:00.005+11:00

The problem

Let's say we want to check the correct mimetype and file extension of the file being uploaded. In a typical Java way I would write something like this:

boolean isRightType = "image/jpeg".equals(contentType)
    || "image/png".equals(contentType)
    || "image/x-png".equals(contentType);

boolean isRightFileExt = filename.endsWith(".png")
    || filename.endsWith(".jpg")
    || filename.endsWith(".jpeg");

Groovy solution

The Groovy way is much simpler and more elegant.

private static CONTENT_TYPES = ["image/jpeg", "image/png", "image/x-png"]
private static FILE_EXTENTIONS = [".png", ".jpg", ".jpeg"]
...
boolean isRightType = CONTENT_TYPES.any { it.equals(contentType) }
boolean isRightFileExt = FILE_EXTENTIONS.any { filename.endsWith(it) }

This was just a small example. What I really find useful are some of the following constructs that make my programming life really pleasant

Groovy Iteration

each

Simple collection iteration

def fibList = [1, 1, 2, 3, 5, 8, 13]
fibList.each { println it }  // prints all of the numbers in the list