Validating input in Spray

In Spray, you get a lot of input validations for free. If you have a model like this:

See here for the whole example.

All the attributes are required. So if you try to post a robot without a name.

You’ll get http 400 with this message:

The types are also checked.


It is possible to make a value optional with Option.

And we can add extra requirements with ‘require’. In the second parameter we can write a nice readable message.

Now when we post an impossible robot.

We get a nice error message.

This way you can make as complex and informative as you want.

Groovy Goodness: Share Data in Concurrent Environment with Dataflow Variables

To work with data in a concurrent environment can be complex. Groovy includes GPars, yes we don’t have to download any dependencies, to provide some models to work easily with data in a concurrent environment. In this blog post we are going to look at an example where we use dataflow variables to exchange data between concurrent tasks. In a dataflow algorithm we define certain functions or tasks that have an input and output. A task is started when the input is available for the task. So instead of defining an imperative sequence of tasks that need to be executed, we define a series of tasks that will start executing when their input is available. And the nice thing is that each of these tasks are independent and can run in parallel if needed.
The data that is shared between tasks is stored in dataflow variables. The value of a dataflow variable can only be set once, but it can be read multiple times. When a task wants to read the value, but it is not yet available, the task will wait for the value in a non-blocking way.

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Grails Goodness: Custom Data Binding with @DataBinding Annotation

Grails has a data binding mechanism that will convert request parameters to properties of an object of different types. We can customize the default data binding in different ways. One of them is using the @DataBinding annotation. We use a closure as argument for the annotation in which we must return the converted value. We get two arguments, the first is the object the data binding is applied to and the second is the source with all original values of type SimpleMapDataBindingSource. The source could for example be a map like structure or the parameters of a request object.

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