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= Groovy Development Kit

include::{projectdir}/src/spec/doc/working-with-io.adoc[leveloffset=+1]

include::{projectdir}/src/spec/doc/working-with-collections.adoc[leveloffset=+1]

== Handy utilities

=== ConfigSlurper

`ConfigSlurper` is a utility class for reading configuration files defined in the form of Groovy scripts. Like it is
the case with Java `*.properties` files, `ConfigSlurper` allows a dot notation. But in addition, it allows for Closure scoped
configuration values and arbitrary object types.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=arbitrary_types,indent=0]
----
<1> Usage of the dot notation
<2> Usage of Closure scopes as an alternative to the dot notation

As can be seen in the above example, the `parse` method can be used to retrieve `groovy.util.ConfigObject` instances. The
`ConfigObject` is a specialized `java.util.Map` implementation that either returns the configured value or a new `ConfigObject`
instance but never `null`.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=never_null,indent=0]
----
<1> `config.test` has not been specified yet it returns a `ConfigObject` when being called.

In the case of a dot being part of a configuration variable name, it can be escaped by using single or double quotes.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=escape_dot,indent=0]
----

In addition, `ConfigSlurper` comes with support for `environments`. The `environments` method can be used to hand over
a Closure instance that itself may consist of a several sections. Let's say we wanted to create a particular configuration
value for the development environment. When creating the `ConfigSlurper` instance we can use the `ConfigSlurper(String)`
constructor to specify the target environment.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=environments,indent=0]
----

[NOTE]
The `ConfigSlurper` environments aren't restricted to any particular environment names. It solely depends on the
`ConfigSlurper` client code what value are supported and interpreted accordingly.

The `environments` method is built-in but the `registerConditionalBlock` method can be used to register other method names
in addition to the `environments` name.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=custom_environments,indent=0]
----
<1> Once the new block is registered `ConfigSlurper` can parse it.

For Java integration purposes the `toProperties` method can be used to convert the `ConfigObject` to a `java.util.Properties`
object that might be stored to a `*.properties` text file. Be aware though that the configuration values are converted to
`String` instances during adding them to the newly created `Properties` instance.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ConfigSlurperTest.groovy[tags=properties,indent=0]
----

=== Expando

The `Expando` class can be used to create a dynamically expandable object. Despite its name it does not use the
`ExpandoMetaClass` underneath. Each `Expando` object represents a standalone, dynamically-crafted instance that can be
extended with properties (or methods) at runtime.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ExpandoTest.groovy[tags=expando_property,indent=0]
----

A special case occurs when a dynamic property registers a `Closure` code block. Once being registered it can be invoked
as it would be done with a method call.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ExpandoTest.groovy[tags=expando_method,indent=0]
----

=== Observable list, map and set

Groovy comes with observable lists, maps and sets. Each of these collections trigger `java.beans.PropertyChangeEvent` events when elements
are added, removed or changed. Note that a `PropertyChangeEvent` is not only signalling that a certain event has
 occurred, moreover, it holds information on the property name and the old/new value a certain property has been changed to.

Depending on the type of change that has happened, observable collections might fire more specialized `PropertyChangeEvent`
 types. For example, adding an element to an observable list fires an `ObservableList.ElementAddedEvent` event.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ObservableTest.groovy[tags=observable_list,indent=0]
----
<1> Declares a `PropertyChangeEventListener` that is capturing the fired events
<2> `ObservableList.ElementEvent` and its descendant types are relevant for this listener
<3> Registers the listener
<4> Creates an `ObservableList` from the given list
<5> Triggers an `ObservableList.ElementAddedEvent` event

[NOTE]
Be aware that adding an element in fact causes two events to be triggered. The first is of type `ObservableList.ElementAddedEvent`,
the second is a plain `PropertyChangeEvent` that informs listeners about the change of property `size`.

The `ObservableList.ElementClearedEvent` event type is another interesting one. Whenever multiple
 elements are removed, for example when calling `clear()`, it holds the elements being removed from the list.

[source,groovy]
----
include::{projectdir}/src/spec/test/gdk/ObservableTest.groovy[tags=observable_list_clear,indent=0]
----

To get an overview of all the supported event types the reader is encouraged to have a look at the JavaDoc documentation
or the source code of the observable collection in use.

`ObservableMap` and `ObservableSet` come with the same concepts as we have seen for `ObservableList` in this section.

