Tuesday, October 8, 2013

Scala: get rid of not-null validations

Martin Podval
Scala has been always known as a language which allows special handling of null values. There is ton of articles regarding Some[T], None, Option[T].

What is most annoying code for me? Null validations, see usual example:


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class Entity {

}

class ServiceA {
  def method(a: Entity, b: Entity, c: Entity, d: Entity) = {
    Validate.notNull(a)
    Validate.notNull(b)
    Validate.notNull(c)
    Validate.notNull(d)
  }
}

class ServiceB(val a: ServiceA) {
  def method() = {
    a.method(null,null,null,null)
  }
}

When you start to write save code in the term of fails-as-fast-as-possible, your code, services or even domain model, will be weedy, you will find such boilerplate code at every method because you can't be sure which parameter supplied someone to you class or method.

Unfortunately Scala has beautiful way how to achieve nice and simple code - without these checks. If you don't think that null is proper state for your class, just dismiss this option. How to do that?


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class Entity extends NotNull{

}

Well, that's all. Look at screenshot from my IDE what is about to happen:

notNull trait scala

Now, if you are sure that you don't want to allow null value for your entity, you can implement NotNull trait and you can remove many lines from your source code.

I was surprised when I found this trait in scala code, because many tutorials or even famous Scala for the Impatient book does not mention this simple but beautiful piece of code.

Tuesday, October 1, 2013

Tomcat 7 remote deployment

Martin Podval
I decided to provide automatic deployment of war packaged application using Jenkins and Deployment plugin. The target platform is Amazon with Tomcat 7, see nice set of articles to find out how to setup such environment for free.

Well, there is couple of tutorials but they missing some points so it pushed me to lost one hour of my work.

What I got

  • Fresh installation of Tomcat 7 on remote machine with opened 8080 port on firewall
  • Personal war file supposed to be deployed

How to push it to tomcat?


1. First of all, there is simple configuration of tomcat users in file tomcat-users.xml - it was my pain in the ass :-) As original comprehensive documentation says, it's necessary to define user, but which one(s)?

Here is working example of tomcat-users.xml:

<tomcat-users>
<user username="manager-gui" password="changeit" roles="manager-gui"/>
<user username="manager-script" password="changeit" roles="manager-script"/>
</tomcat-users>

The important part is manager-script, contrary to Tomcat 6 where it had not exist yet. This user allows access to /text sub-namespace in management uri. The first user called manager-gui is the one which you use in GUI console, e.g. http://localhost:8085/manager/html

Once you run tomcat using bin's bat file, you can move to second bullet.

2. Now, it's possible to use remote deployment using curl command, e.g. in my use-case:

curl --upload-file my.war "http://manager-script:changeit@localhost:8080/manager/text/deploy?path=/myPath&update=true"

The command is working using manager-script user contrary to my original manager-gui. Another interesting part is path=/myPath. This attribute say which URL sub-namespace is to be used.

Even if you deploy my.war and common Tomcat's approach is to deploy application in /my subname, the application is to be exposed on /myPath.

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