org.rythmengine.extension

Annotation Type Transformer

@Retention(value=RUNTIME)
 @Target(value={METHOD,TYPE})
public @interface Transformer

Transformer could be used to annotate on a public static methods that works on a given object with or without parameters. For example,

@Transformer public static String format(Number number, String formatStr)

When feature.transformer.enabled is set to true (by default it is true), template author can use Transformer to further process an expression value:

@args Date dueDate\n…@dueDate.format(“dd/MM/yyyy”)

The @dueDate.format(“dd/MM/yyyy”) in the above example will be transformed into S.format(dueDate, “dd/MM/yyyy”) in the generated java source

Note, the above sample code demonstrates a transformer named format, which is built into Rythm engine. However when you want to define your own transformer, you need to use this Transformer annotation to mark on your methods or classes. When the annotation is marked on a class, then all public static methods with return value and at least one parameter will be treated as transformer

You can register them to RythmEngine by RythmEngine.registerTransformer(Class[]) method

, once you have registered your Java extension methods, the template author can use them in template. Be careful of the name conflict of your Java extension and Rythm’s built-in Java extension. You can turn off rythm’s built java extension by set “rythm.disableBuiltInTransformer” to true

Transformers mechanism is also found in other template engine solutions, but with different names. Freemarker call it built-ins, Velocity called it velocity tools. But none of them are as easy to use as Rythm Transformers

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
boolean	lastParam Indicate whether the expression been transformed should be passed to the transformer function as first or last param
boolean	requireTemplate Require passing template instance as implicit argument (the first parameter)
String	value The namespace of the transformer.
String	waivePattern Once specified the pattern will be used to match the token to see if transformer extension should be waived or not.

Element Detail

value

public abstract String value

The namespace of the transformer. When namespace is presented, the template author needs to use the namespace to qualify the transformer in the template source. For example, @x.app_myTransformer()

Default value: "app"

Returns:

the namespace

Default:

"app"

waivePattern

public abstract String waivePattern

Once specified the pattern will be used to match the token to see if transformer extension should be waived or not. For example, @x.escape() should be treated as escape transformer while @s().escape(x) shouldn’t because s\(\) is a waive pattern

Returns:

the waive pattern

Default:

""

requireTemplate

public abstract boolean requireTemplate

Require passing template instance as implicit argument (the first parameter)

Returns:

true if require passing template instance as the implicit first parameter

Default:

false

lastParam

public abstract boolean lastParam

Indicate whether the expression been transformed should be passed to the transformer function as first or last param

Returns:

true if the expression been transformed should be passed in as the last param.

Default:

false