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Singleton

org.openrewrite.Singleton

Used as a precondition to ensure that a recipe attempts to make changes only once. Accidentally including multiple copies/instances of the same large composite recipes is a common mistake. If those recipes are marked with this precondition the performance penalty is limited. This recipe does nothing useful run on its own.

Usage in YAML recipes​

Add org.openrewrite.Singleton as a precondition:

---
type: specs.openrewrite.org/v1beta/recipe
name: com.example.Append
displayName: My recipe
preconditions:
  - org.openrewrite.Singleton
recipeList:
  - org.openrewrite.text.AppendToTextFile:
      relativeFileName: report.txt
      content: 'Recipe executed'
```## Usage in Java recipes

Wrap visitors with `Singleton.singleton(this, visitor)` to ensure only the first *equivalent* recipe instance makes changes:

```java
@Override
public TreeVisitor<?, ExecutionContext> getVisitor(Accumulator acc) {
    return singleton(this, new TreeVisitor<Tree, ExecutionContext>() {
        @Override
        public Tree visit(@Nullable Tree tree, ExecutionContext ctx) {
            // Your transformation logic
            return tree;
        }
    });
}
@Override
public Collection<SourceFile> generate(Accumulator acc, ExecutionContext ctx) {
    if (!isSingleton(this, ctx)) {
        return Collections.emptyList();
    }
    // Generate new sources
    return results;
}

@Override
public TreeVisitor<?, ExecutionContext> getVisitor(Accumulator acc) {
    return singleton(this, new TreeVisitor<Tree, ExecutionContext>() {
        // Visitor logic
    });
}

Note: Singleton status is determined by the recipe's equals() and hashCode() methods. If equivalent instances of a recipe are not considered singletons, ensure your recipe class correctly implements these methods. The easiest way is to use Lombok's @Value annotation on your recipe class, which automatically generates correct equals() and hashCode() implementations based on all fields.

Recipe source​

GitHub: Singleton.java, Issue Tracker, Maven Central

This recipe is available under the Apache License Version 2.0.

Usage​

This recipe has no required configuration parameters and comes from a rewrite core library. It can be activated directly without adding any dependencies.

  1. Add the following to your build.gradle file:
build.gradle
plugins {
    id("org.openrewrite.rewrite") version("latest.release")
}

rewrite {
    activeRecipe("org.openrewrite.Singleton")
    setExportDatatables(true)
}

repositories {
    mavenCentral()
}

  1. Run gradle rewriteRun to run the recipe.

See how this recipe works across multiple open-source repositories​

Run this recipe on OSS repos at scale with the Moderne SaaS.

The community edition of the Moderne platform enables you to easily run recipes across thousands of open-source repositories.

Please contact Moderne for more information about safely running the recipes on your own codebase in a private SaaS.

Data Tables​

Source files that had results​

org.openrewrite.table.SourcesFileResults

Source files that were modified by the recipe run.

Column NameDescription
Source path before the runThe source path of the file before the run. null when a source file was created during the run.
Source path after the runA recipe may modify the source path. This is the path after the run. null when a source file was deleted during the run.
Parent of the recipe that made changesIn a hierarchical recipe, the parent of the recipe that made a change. Empty if this is the root of a hierarchy or if the recipe is not hierarchical at all.
Recipe that made changesThe specific recipe that made a change.
Estimated time savingAn estimated effort that a developer to fix manually instead of using this recipe, in unit of seconds.
CycleThe recipe cycle in which the change was made.