add nextflow d30e48d

nextflow/docs/reference/stdlib-groovy.md

@@ -0,0 +1,25 @@
+(stdlib-groovy)=
+
+# Groovy and Java classes
+
+Any Groovy or Java class that is available to Nextflow at runtime can be used in a Nextflow script. The following classes are imported by default:
+
+- `groovy.lang.*`
+- `groovy.util.*`
+- `java.io.*`
+- `java.lang.*`
+- `java.math.BigDecimal`
+- `java.math.BigInteger`
+- `java.net.*`
+- `java.util.*`
+
+All other classes must be referenced by their fully-qualified name:
+
+```nextflow
+def vals = [1, 2, 3]
+println groovy.json.JsonOutput.toJson(vals)
+```
+
+:::{note}
+The set of classes in Nextflow's runtime classpath can change between different Nextflow versions. As a best practice, any code that uses classes outside the Nextflow standard library should either be refactored to only use the Nextflow standard library or be refactored as a {ref}`plugin <dev-plugins-page>` with explicit dependencies.
+:::