Add RedundantUtf8Charset recipe to drop redundant UTF-8 from Files calls

src/main/java/org/openrewrite/java/migrate/nio/file/RedundantUtf8Charset.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (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://docs.moderne.io/licensing/moderne-source-available-license
+ * <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.nio.file;
+
+import lombok.Getter;
+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.MethodMatcher;
+import org.openrewrite.java.search.UsesType;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
+import org.openrewrite.java.tree.TypeUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RedundantUtf8Charset extends Recipe {
+
+    private static final List<MethodMatcher> MATCHERS = new ArrayList<>();
+
+    static {
+        for (String signature : new String[]{
+                "java.nio.file.Files readString(java.nio.file.Path, java.nio.charset.Charset)",
+                "java.nio.file.Files writeString(java.nio.file.Path, java.lang.CharSequence, java.nio.charset.Charset, ..)",
+                "java.nio.file.Files readAllLines(java.nio.file.Path, java.nio.charset.Charset)",
+                "java.nio.file.Files write(java.nio.file.Path, java.lang.Iterable, java.nio.charset.Charset, ..)",
+                "java.nio.file.Files lines(java.nio.file.Path, java.nio.charset.Charset)",
+                "java.nio.file.Files newBufferedReader(java.nio.file.Path, java.nio.charset.Charset)",
+                "java.nio.file.Files newBufferedWriter(java.nio.file.Path, java.nio.charset.Charset, ..)"}) {
+            MATCHERS.add(new MethodMatcher(signature));
+        }
+    }
+
+    @Getter
+    final String displayName = "Remove redundant `StandardCharsets.UTF_8` from `java.nio.file.Files` method calls";
+
+    @Getter
+    final String description = "The character based `java.nio.file.Files` methods always default to UTF-8, so passing " +
+                               "`StandardCharsets.UTF_8` explicitly is redundant and can be removed.";
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return Preconditions.check(new UsesType<>("java.nio.charset.StandardCharsets", false), new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
+                J.MethodInvocation mi = super.visitMethodInvocation(method, ctx);
+                if (MATCHERS.stream().noneMatch(m -> m.matches(mi))) {
+                    return mi;
+                }
+                List<Expression> arguments = mi.getArguments();
+                for (int i = 0; i < arguments.size(); i++) {
+                    if (isUtf8(arguments.get(i))) {
+                        List<Expression> newArguments = new ArrayList<>(arguments);
+                        newArguments.remove(i);
+                        maybeRemoveImport("java.nio.charset.StandardCharsets");
+
+                        JavaType.Method methodType = mi.getMethodType();
+                        if (methodType != null && i < methodType.getParameterTypes().size()) {
+                            List<JavaType> parameterTypes = new ArrayList<>(methodType.getParameterTypes());
+                            List<String> parameterNames = new ArrayList<>(methodType.getParameterNames());
+                            parameterTypes.remove(i);
+                            parameterNames.remove(i);
+                            methodType = methodType.withParameterTypes(parameterTypes).withParameterNames(parameterNames);
+                        }
+                        return mi.withArguments(newArguments)
+                                .withMethodType(methodType)
+                                .withName(mi.getName().withType(methodType));
+                    }
+                }
+                return mi;
+            }
+
+            private boolean isUtf8(Expression argument) {
+                if (!TypeUtils.isOfClassType(argument.getType(), "java.nio.charset.Charset")) {
+                    return false;
+                }
+                if (argument instanceof J.FieldAccess) {
+                    J.FieldAccess fieldAccess = (J.FieldAccess) argument;
+                    return "UTF_8".equals(fieldAccess.getSimpleName()) &&
+                           TypeUtils.isOfClassType(fieldAccess.getTarget().getType(), "java.nio.charset.StandardCharsets");
+                }
+                if (argument instanceof J.Identifier) {
+                    J.Identifier identifier = (J.Identifier) argument;
+                    JavaType.Variable fieldType = identifier.getFieldType();
+                    return "UTF_8".equals(identifier.getSimpleName()) && fieldType != null &&
+                           TypeUtils.isOfClassType(fieldType.getOwner(), "java.nio.charset.StandardCharsets");
+                }
+                return false;
+            }
+        });
+    }
+}

src/main/java/org/openrewrite/java/migrate/nio/file/package-info.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (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://docs.moderne.io/licensing/moderne-source-available-license
+ * <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.
+ */
+@NullMarked
+@NonNullFields
+package org.openrewrite.java.migrate.nio.file;
+
+import org.jspecify.annotations.NullMarked;
+import org.openrewrite.internal.lang.NonNullFields;

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

@@ -57,6 +57,7 @@ recipeList:
   - org.openrewrite.java.migrate.lombok.UpdateLombokToJava11
   - org.openrewrite.java.migrate.net.JavaNetAPIs
   - org.openrewrite.java.migrate.nio.file.PathsGetToPathOf
+  - org.openrewrite.java.migrate.nio.file.RedundantUtf8Charset
   - org.openrewrite.java.migrate.sql.JavaSqlAPIs
   - org.openrewrite.java.migrate.javax.JavaxLangModelUtil
   - org.openrewrite.java.migrate.javax.JavaxManagementMonitorAPIs