Optional<Stream>.filter(Optional::isPresent).map(Optional::get) to Java 11 .flatMap(Optional::stream)

src/main/java/org/openrewrite/java/migrate/util/OptionalStreamRecipe.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2023 the original author or authors.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.migrate.util;
+
+import org.jetbrains.annotations.NotNull;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.JavaTemplate;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.search.UsesMethod;
+import org.openrewrite.java.tree.*;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class OptionalStreamRecipe extends Recipe {
+    @Override
+    public String getDisplayName() {
+        return "`Stream<Optional>` idiom recipe";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Migrate Java 8 `Optional<Stream>.filter(Optional::isPresent).map(Optional::get)` to Java 11 `.flatMap(Optional::stream)`.";
+    }
+
+    private static final MethodMatcher mapMatcher = new MethodMatcher("java.util.stream.Stream map(java.util.function.Function)");
+    private static final MethodMatcher filterMatcher = new MethodMatcher("java.util.stream.Stream filter(java.util.function.Predicate)");
+    private static final MethodMatcher optionalGetMatcher = new MethodMatcher("java.util.Optional get()");
+    private static final MethodMatcher optionalIsPresentMatcher = new MethodMatcher("java.util.Optional isPresent()");
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return Preconditions.check(new UsesMethod<>(optionalIsPresentMatcher), new OptionalStreamVisitor());
+    }
+
+    private static class OptionalStreamVisitor extends JavaIsoVisitor<ExecutionContext> {
+        private static final JavaTemplate template =
+                JavaTemplate.builder("#{any(java.util.stream.Stream)}.flatMap(Optional::stream)")
+                        .imports("java.util.Optional")
+                        .build();
+
+        @Override
+        public J.MethodInvocation visitMethodInvocation(J.MethodInvocation invocation, ExecutionContext ctx) {
+            J.MethodInvocation mapInvocation = super.visitMethodInvocation(invocation, ctx);
+            // .map(Optional::get)
+            if (!mapMatcher.matches(mapInvocation) || !optionalGetMatcher.matches(mapInvocation.getArguments().get(0))) {
+                return mapInvocation;
+            }
+            // .filter
+            Expression mapSelectExpr = mapInvocation.getSelect();
+            if (!filterMatcher.matches(mapSelectExpr)) {
+                return mapInvocation;
+            }
+            // Optional::isPresent
+            J.MethodInvocation filterInvocation = (J.MethodInvocation) mapSelectExpr;
+            if (!optionalIsPresentMatcher.matches(filterInvocation.getArguments().get(0))) {
+                return mapInvocation;
+            }
+
+            JRightPadded<Expression> filterSelect = filterInvocation.getPadding().getSelect();
+            JRightPadded<Expression> mapSelect = mapInvocation.getPadding().getSelect();
+            JavaType.Method mapInvocationType = mapInvocation.getMethodType();
+            Space flatMapComments = getFlatMapComments(mapSelect, filterSelect);
+            J.MethodInvocation flatMapInvocation = template
+                    .apply(updateCursor(mapInvocation), mapInvocation.getCoordinates().replace(), filterInvocation.getSelect());
+            return flatMapInvocation.getPadding()
+                    .withSelect(filterSelect.withAfter(flatMapComments))
+                    .withMethodType(mapInvocationType.withName("flatMap"))
+                    .withPrefix(mapInvocation.getPrefix());
+        }
+
+        @NotNull
+        private static Space getFlatMapComments(JRightPadded<Expression> mapSelect, JRightPadded<Expression> filterSelect) {
+            List<Comment> comments = new ArrayList<>();
+            comments.addAll(filterSelect.getAfter().getComments());
+            comments.addAll(mapSelect.getAfter().getComments());
+            return filterSelect.getAfter().withComments(comments);
+        }
+    }
+}

src/main/resources/META-INF/rewrite/java-version-11.yml

@@ -56,6 +56,7 @@ recipeList:
 #  - org.openrewrite.java.migrate.util.JavaUtilAPIs
   - org.openrewrite.java.migrate.util.OptionalNotPresentToIsEmpty
   - org.openrewrite.java.migrate.util.OptionalNotEmptyToIsPresent
+  - org.openrewrite.java.migrate.util.OptionalStreamRecipe
   - org.openrewrite.github.SetupJavaUpgradeJavaVersion:
       minimumJavaMajorVersion: 11
   - org.openrewrite.java.migrate.InternalBindContextFactory