Openrewrite Recipes

Use MethodMatcher for method+type validation

Instead of manually checking method name and receiver type:

// BAD
if (!"getMessage".equals(method.getSimpleName())) return false;
Expression select = method.getSelect();
if (select == null) return false;
return TypeUtils.isAssignableTo("java.lang.Throwable", select.getType());

// GOOD
private static final MethodMatcher GET_MESSAGE = new MethodMatcher("java.lang.Throwable getMessage()");
// then: GET_MESSAGE.matches(argument)

TypeUtils

Use isOfClassType() instead of manual FQN comparison

// BAD
JavaType.FullyQualified type = TypeUtils.asFullyQualified(select.getType());
return type != null && "org.slf4j.Logger".equals(type.getFullyQualifiedName());

// GOOD
TypeUtils.isOfClassType(select.getType(), "org.slf4j.Logger")

Use TypeUtils.isOfType() instead of FQN string equality

// BAD
currentType.getFullyQualifiedName().equals(targetType.getFullyQualifiedName())

// GOOD
TypeUtils.isOfType(currentType, targetType)

Handle inheritance with isAssignableTo()

When matching a member's declaring type against the current class, check both exact match and subtype relationship. Without this, inherited members get incorrectly attributed to the superclass:

// BAD: misses inherited members
if (TypeUtils.isOfType(currentType, declaringType)) { ... }

// GOOD: handles both direct and inherited members
if (TypeUtils.isOfType(currentType, declaringType) ||
        TypeUtils.isAssignableTo(declaringType.getFullyQualifiedName(), currentType)) { ... }

Use the FQN-based isAssignableTo overload to handle parameterized types correctly.

Use instanceof JavaType.FullyQualified not JavaType.Class

JavaType.Class extends JavaType.FullyQualified, so checking for the parent type is broader and more correct:

// BAD: too narrow
if (fieldType.getOwner() instanceof JavaType.Class)

// GOOD: covers more cases
if (fieldType.getOwner() instanceof JavaType.FullyQualified)

ListUtils for Statement Transformations

Use ListUtils.flatMap() instead of manual ArrayList + modified flag

// BAD
List<Statement> newStatements = new ArrayList<>();
boolean modified = false;
for (Statement stmt : visited.getStatements()) {
    if (shouldTransform(stmt)) {
        newStatements.addAll(extractStatements(stmt));
        modified = true;
    } else {
        newStatements.add(stmt);
    }
}
if (modified) return visited.withStatements(newStatements);
return visited;

// GOOD
return visited.withStatements(ListUtils.flatMap(visited.getStatements(), stmt -> {
    if (shouldTransform(stmt)) {
        return extractStatements(stmt); // return List = replace with multiple
    }
    return stmt; // return single item = keep as-is
}));

Use ListUtils.map() and ListUtils.mapFirst() for whitespace adjustments

List<Statement> bodyStatements = ListUtils.map(
    extractStatements(ifStmt.getThenPart()),
    st -> st.withPrefix(Space.build(whitespace, emptyList())));
return ListUtils.mapFirst(bodyStatements,
    first -> first.withPrefix(ifStmt.getPrefix()));

Recipe Composition

Don't duplicate logic handled by earlier recipes

When recipes run in a composition (e.g., Slf4jBestPractices), earlier recipes transform the code before later ones see it. Don't handle cases that earlier recipes already cover.

Example: RemoveUnnecessaryLogLevelGuards should NOT treat string concatenation ("Name: " + name) as safe to unguard. The ParameterizedLogging recipe runs first and converts concatenation to parameterized form. If concatenation still exists when the guard-removal recipe runs, the guard is still needed for performance.

Add test cases for edge cases where transformation should NOT apply

Always test that the recipe correctly preserves code that should not be changed, not just that it transforms code that should be changed.

AST Construction

Use JavaElementFactory for common nodes

// BAD: verbose manual construction
new J.Identifier(Tree.randomId(), Space.EMPTY, Markers.EMPTY, emptyList(), "this", ownerType, null)

// GOOD: factory method
JavaElementFactory.newThis(ownerType)

Use Flag enum and modifier helpers instead of magic bitmasks

// BAD: magic number
(fieldType.getFlagsBitMap() & 0x0008L) != 0

// GOOD: readable API
fieldType.hasFlags(Flag.Static)
method.hasModifier(J.Modifier.Type.Static)

Language Scoping

Exclude non-target languages from Java-specific recipes

Java-specific recipes will also run on Kotlin files unless explicitly excluded:

@Override
public TreeVisitor<?, ExecutionContext> getVisitor() {
    return Preconditions.check(
        Preconditions.not(new KotlinFileChecker<>()),
        new MyJavaVisitor()
    );
}

JavaTemplate Usage

Declare imports when the template introduces types

JavaTemplate template = JavaTemplate.builder("#{any()}.toArray(new #{}[0])")
        .imports(fqn)  // Declare the import
        .build();

Always call maybeAddImport() after applying a template

After applying a template that uses a type, add the import to the compilation unit:

Expression result = template.apply(...);
maybeAddImport(fqn);  // Add the import to the source file

Visitor Patterns

JavaVisitor vs JavaIsoVisitor

Use JavaIsoVisitor when returning the same LST element type you're visiting (most common for simple transformations):

@Override
public J.TypeCast visitTypeCast(J.TypeCast typeCast, ExecutionContext ctx) {
    J.TypeCast tc = super.visitTypeCast(typeCast, ctx);
    // ... transform ...
    return tc;  // Still a J.TypeCast
}

Use JavaVisitor when you need to return a different LST element type (e.g., unwrapping parentheses):

@Override
public J visitParentheses(J.Parentheses parentheses, ExecutionContext ctx) {
    // ... some logic ...
    return someExpression;  // Not a J.Parentheses
}

Handle parenthesized expressions explicitly

When dealing with expressions that might be parenthesized, visit J.Parentheses nodes too.

Preserve formatting when replacing expressions

return visitedParentheses.withTree(result);  // Preserves parentheses structure and prefix

Recipe Metadata

Include RSPEC tags for SonarQube rules

@Override
public Set<String> getTags() {
    return Collections.singleton("RSPEC-S3020");
}

Provide accurate time estimates

Use the same time estimate from the SonarQube definition:

@Override
public Duration getEstimatedEffortPerOccurrence() {
    return Duration.ofMinutes(2);
}

YAML Configuration

Add recipes to appropriate recipe collections

Don't forget to add new recipes to relevant YAML files:

recipeList:
    - org.openrewrite.staticanalysis.CollectionToArrayShouldHaveProperType

Common collections:

• common-static-analysis.yml - General static analysis fixes
• java-best-practices.yml - Java-specific best practices
• static-analysis.yml - Broader static analysis recipes

At-Scale Validation

Test recipes against real-world codebases

Before submitting, run at scale against large codebases (e.g., Spring, Netflix orgs). This catches bugs unit tests miss:

• Inherited members being incorrectly qualified (e.g., SuperClass.this.method() instead of this.method())
• Recipes accidentally modifying Kotlin files (see Language Scoping above)

Code Style

• Explicit imports over wildcards (java.util.List not java.util.*)
• Static imports for Collections.emptyList() and singletonList()
• @Nullable from org.jspecify.annotations on methods that can return null
• Don't add @NonNull on parameters (non-null is the default)
• Inline small single-use helper methods rather than creating many tiny private methods
• Ternary for simple conditional returns
• Pass pre-validated/cast values as parameters rather than re-checking inside helper methods