DDevelopment & Design

Rapid js + css development

BackgroundLast time I had some work to do in OSGi web module written in Spring MVC. If we have application splitted to well-designed modules, back-end development in this framework run in OSGi environment is quite fast because after some modification w…

Background

Last time I had some work to do in

OSGi web module written in Spring MVC. If we have application splitted to well-designed modules, back-end development in this framework run in OSGi environment is quite fast because after some modification we must update only one bundle (without dependencies). But programming in front-end is much less dynamic than in in modern frameworks like Ruby or Groovy. There is no build-in support to update resources “on the fly” after their modification (or I can’t find it).

There is many plugins to web browser which help you build front-end from scratch in wysiwyg mode. But I can’t find any which could modify resources of already ran application. Also it will be complicated to keep synchronized these modifications with our sources. Therefore I tried to use local links to my project in my application. I put code similar to this below in my page.
After redeploy I found in my Chromium console: Error::Not allowed to load local resource: file:///path/to/my/local/resource.js. After some googling I found solution: adding –allow-file-access-from-files switch to application. Unfortunately it doesn’t work on my Chromium v.18. I also checked other switches: –disable-web-security and –allow-file-access but with no effect. I also tried  LocalLinks plugin but with the same result.

Solution

I found out that the simplest walkaround to this problem is to link my local resources directory in Apache2 web root. So i did this:

After this inclusion of script looks like:

As you can see, it is only difference in port in new location of script. So maybe there is a tool which helps in automatic replace this string?

Tampermonkey script

In

Firefox I’ve been using Greasemonkey plugin which could do automatic code replacement like this on the fly. On Chrome there is Tampermonkey which is a port of Greasemonkey. I wrote script which do this thing for me:

What the script do?

It simply add on end of

script includes from location with replaced string from -> to. It also modify CSS link hrefs using the same approach. Both scripts and links are filtered using blacklist – it is helpful if our application using external resources.

Result

Now I can spend all of my time intended for development only writing a code. After any modification I only refresh a page in browser (I’m using

IntelliJ Idea so instant autosaving is working for me). And what solutions of this problem you are using?

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DDevelopment & Design

Log4j and MDC in Grails

Log4j provides very useful feature: MDC - mapped diagnostic context. It can be used to store data in context of current thread. It may sound scary a bit but idea is simple.

My post is based on post http://burtbeckwith.com/blog/?p=521 from Burt Beckwith's excellent blog, it's definitely worth checking if you are interested in Grails.

Short background story...


Suppose we want to do logging our brand new shopping system and we want to have in each log customer's shopping basket number. And our system can be used at once by many users who can perform many transactions, actions like adding items and so on. How can we achieve that? Of course we can add basket number in every place where we do some logging but this task would be boring and error-prone. 

Instead of this we can use MDC to store variable with basket number in map. 

In fact MDC can be treated as map of custom values for current thread that can be used by logger. 


How to do that with Grails?


Using MDC with Grails is quite simple. All we need to do is to create our own custom filter which works for given urls and puts our data in MDC.

Filters in Grails are classes in directory grails-app/conf/* which names end with *Filters.groovy postfix. We can create this class manually or use Grails command: 
grails create-filters info.rnowak.App.Basket

In result class named BasketFilters will be created in grails-app/conf/info/rnowak/UberApp.

Initially filter class looks a little bit empty:
class BasketFilters {
    def filters = {
        all(controller:'*', action:'*') {
            before = {

            }
            after = { Map model ->

            }
            afterView = { Exception e ->

            }
        }
    }
}
All we need to do is fill empty closures, modify filter properties and put some data into MDC.

all is the general name of our filter, as class BasketFilters (plural!) can contain many various filters. You can name it whatever you want, for this post let assume it will be named basketFilter. 

Another thing is change of filter parameters. According to official documentation (link) we can customize our filter in many ways. You can specify controller to be filtered, its actions, filtered urls and so on. In our example you can stay with default option where filter is applied to every action of every controller. If you are interested in filtering only some urls, use uri parameter with expression describing desired urls to be filtered.

Three closures that are already defined in template have their function and they are started in these conditions:

  • before - as name says, it is executed before filtered action takes place
  • after - similarly, it is called after the action
  • afterView - called after rendering of the actions view
Ok, so now we know what are these mysterious methods and when they are called. But what can be done within them? In official Grails docs (link again) under section 7.6.3 there is a list of properties that are available to use in filter.

With that knowledge, we can proceed to implementing filter.

Putting something into MDC in filter


What we want to do is quite easy: we want to retrieve basket number from parameters and put it into MDC in our filter:
class BasketFilters {
    def filters = {
        basketFilter(controller:'*', action:'*') {
            before = {
                MDC.put("basketNumber", params.basketNumber ?: "")
            }
            after = { Map model ->
                MDC.remove("basketNumber")
            }
        }
    }
}

We retrieve basket number from Grails params map and then we put in map under specified key ("basketNumber" in this case), which will be later used in logger conversion pattern. It is important to remove custom value after processing of action to avoid leaks.

So we are putting something into MDC. But how make use of it in logs?


We can refer to custom data in MDC in conversion patter using syntax: %X{key}, where key is our key we used in filter to put data, like:
def conversionPattern = "%d{yyyy-MM-dd HH:mm:ss} %-5p %t [%c{1}] %X{basketNumber} - %m%n"


And that's it :) We've put custom data in log4j MDC and successfully used it in logs to display interesting values.
DDevelopment & Design

33rd Degree day 3 review

At the last day of the conference, I've decided to skip the first presentations, and get some sleep instead. I was afraid that Venkat's show is going to be too basic, I will see Jacek Laskowski talking about closure at 4Developers, which I'm kind of s...