Sample custom Groovy annotation with AST transformation.
Randomly initialize local variables.
Usage:
@RandomInit(min=1, max=300) Integer int1
@RandomInit(minLength = 10) String str1
Annotations are one of the best way to enhance language power. Build custom annotations in Groovy is pretty easy.
Lets create simple annotation that will randomly initialize annotated number or string variables. This annotation can be useful for example in testing.
First of all we need to declare annotation:
package com.illerax.randominit
import org.codehaus.groovy.transform.GroovyASTTransformationClass
import java.lang.annotation.ElementType
import java.lang.annotation.Retention
import java.lang.annotation.RetentionPolicy
import java.lang.annotation.Target
@Target([ElementType.LOCAL_VARIABLE])
@Retention(RetentionPolicy.SOURCE)
@GroovyASTTransformationClass("com.illerax.randominit.RandomInitTransformation")
@interface RandomInit {
int minLength() default 1
int maxLength() default 100
int min() default 0
int max() default 1
}
Then we need to create transformation code:
package com.illerax.randominit
import org.codehaus.groovy.ast.ASTNode
import org.codehaus.groovy.ast.expr.ConstantExpression
import org.codehaus.groovy.control.CompilePhase
import org.codehaus.groovy.control.SourceUnit
import org.codehaus.groovy.transform.ASTTransformation
import org.codehaus.groovy.transform.GroovyASTTransformation
/**
* Created by Evgeny Smirnov on 01/03/17.
*/
@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)
class RandomInitTransformation implements ASTTransformation {
@Override
void visit(ASTNode[] nodes, SourceUnit source) {
Random random = new Random()
def (annotation, expression) = nodes
switch (expression.variableExpression.type.typeClass) {
case Number:
def min = annotation.members?.min?.value ?: RandomInit.getDeclaredMethod('min').defaultValue
def max = annotation.members?.max?.value ?: RandomInit.getDeclaredMethod('max').defaultValue
expression.rightExpression = new ConstantExpression(random.nextDouble() * (max - min) + min)
break
case String:
String charset = (('a'..'z') + ('A'..'Z') + ('0'..'9') + (' ')).join()
def min = annotation.members?.minLength?.value ?: RandomInit.getDeclaredMethod('minLength').defaultValue
def max = annotation.members?.maxLength?.value ?: RandomInit.getDeclaredMethod('maxLength').defaultValue
Integer len = random.nextInt(max - min + 1) + min
expression.rightExpression = new ConstantExpression(
(1..len).inject('') { result, val -> result += charset[random.nextInt(charset.size())] }
)
break
}
}
}
Implementing ASTTransformation we must override visit method which will be called every time when compiler found our @RandomInit annotations. One of the most important thing building groovy custom annotation is to select correct Compile Phase. There are no out of the box solutions. Which phase is suited best depends on what we want to do with the AST transformation. We use “Semantic Analysis” and it is the earliest phase we can process our custom annotation. Groovy AST Browser may help you to check what happens with code during each phase and which one is best for your annotation.
Usage example:
package test
import com.illerax.randominit.RandomInit
class RandomInitTest extends GroovyTestCase {
void testRandomInitAnnotation() {
@RandomInit def exp
assert exp == null
@RandomInit Integer int1
assert int1 != null
@RandomInit(min = -10, max = 10) Integer int2
assert int2 >= -10
assert int2 <= 10
@RandomInit(min = -100, max = -50) Integer int3
assert int3 >= -100
assert int3 <= -50
@RandomInit(min = 40, max = 100) BigDecimal dec1
assert dec1 >= 40
assert dec1 <= 100
@RandomInit(min = 1, max = 1) BigDecimal dec2
assert dec2 == 1
@RandomInit(minLength = 3, maxLength = 3) String str1
str1.size() == 3
}
}
Useful Links:
https://github.com/illerax/random_init – @RandomInit sources
http://groovy-lang.org/objectorientation.html#_annotation – Official Documentation
http://melix.github.io/ast-workshop/ – Groovy AST Transformations Workshop by Cédric Champeau
http://glaforge.appspot.com/article/groovy-ast-transformations-tutorials – Articles recommended by Guillaume Laforge
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