Add recipe to change logger fields to private

src/main/java/org/openrewrite/java/logging/ChangeLoggersToPrivate.java

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2025 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.logging;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+import org.openrewrite.Cursor;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Recipe;
+import org.openrewrite.Tree;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
+import org.openrewrite.java.tree.Space;
+import org.openrewrite.java.tree.TypeUtils;
+import org.openrewrite.marker.Markers;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class ChangeLoggersToPrivate extends Recipe {
+
+    private static final Set<String> LOGGER_TYPES = Stream.of(LoggingFramework.values())
+            .map(LoggingFramework::getLoggerType)
+            .collect(Collectors.toSet());
+
+    @Override
+    public String getDisplayName() {
+        return "Change logger fields to private";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Ensures that logger fields are declared as 'private' to encapsulate logging mechanics within the class.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.VariableDeclarations visitVariableDeclarations(J.VariableDeclarations multiVariable, ExecutionContext ctx) {
+                Cursor parent = getCursor().getParentTreeCursor();
+                if (!(parent.getValue() instanceof J.Block)) {
+                    return multiVariable;
+                }
+
+                parent = parent.getParentTreeCursor();
+                if (!(parent.getValue() instanceof J.ClassDeclaration)) {
+                    return multiVariable;
+                }
+
+                J.ClassDeclaration classDeclaration = parent.getValue();
+                if (classDeclaration.getKind() == J.ClassDeclaration.Kind.Type.Interface) {
+                    return multiVariable;
+                }
+
+                if (multiVariable.getTypeExpression() == null || !isLoggerType(multiVariable.getTypeExpression().getType())) {
+                    return multiVariable;
+                }
+
+                boolean isPrivate = multiVariable.getModifiers().stream()
+                        .anyMatch(mod -> mod.getType() == J.Modifier.Type.Private);
+                if (isPrivate) {
+                    return multiVariable;
+                }
+
+                List<J.Modifier> newModifiers = new ArrayList<>();
+                newModifiers.add(
+                        new J.Modifier(
+                                Tree.randomId(),
+                                Space.EMPTY,
+                                Markers.EMPTY,
+                                null,
+                                J.Modifier.Type.Private,
+                                Collections.emptyList()
+                        )
+                );
+
+                for (J.Modifier existingModifier : multiVariable.getModifiers()) {
+                    if (existingModifier.getType() != J.Modifier.Type.Public &&
+                            existingModifier.getType() != J.Modifier.Type.Protected &&
+                            existingModifier.getType() != J.Modifier.Type.Private) {
+                        newModifiers.add(existingModifier.withPrefix(Space.SINGLE_SPACE));
+                    }
+                }
+
+                multiVariable = multiVariable.withModifiers(newModifiers)
+                        .withTypeExpression(multiVariable.getTypeExpression().withPrefix(Space.SINGLE_SPACE));
+                return autoFormat(multiVariable, ctx, getCursor().getParent());
+            }
+
+            private boolean isLoggerType(JavaType type) {
+                JavaType.FullyQualified fqnType = TypeUtils.asFullyQualified(type);
+                if (fqnType != null) {
+                    return LOGGER_TYPES.contains(fqnType.getFullyQualifiedName());
+                }
+                return false;
+            }
+        };
+    }
+}

src/main/resources/META-INF/rewrite/examples.yml

@@ -956,3 +956,24 @@ examples:
           }
       }
     language: java
+---
+type: specs.openrewrite.org/v1beta/example
+recipeName: org.openrewrite.java.logging.ChangeLoggersToPrivate
+examples:
+- description: ''
+  sources:
+  - before: |
+      import org.slf4j.Logger;
+      import org.slf4j.LoggerFactory;
+
+      class Test {
+          public static final Logger LOGGER = LoggerFactory.getLogger(Test.class);
+      }
+    after: |
+      import org.slf4j.Logger;
+      import org.slf4j.LoggerFactory;
+
+      class Test {
+          private static final Logger LOGGER = LoggerFactory.getLogger(Test.class);
+      }
+    language: java

src/test/java/org/openrewrite/java/logging/ChangeLoggersToPrivateTest.java

@@ -0,0 +1,195 @@
+/*
+ * Copyright 2025 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.logging;
+
+import org.junit.jupiter.api.Test;
+import org.openrewrite.test.RecipeSpec;
+import org.openrewrite.test.RewriteTest;
+
+import static org.openrewrite.java.Assertions.java;
+
+class ChangeLoggersToPrivateTest implements RewriteTest {
+
+    @Override
+    public void defaults(RecipeSpec spec) {
+        spec.recipe(new ChangeLoggersToPrivate());
+    }
+
+    @Test
+    void changePublicSlf4jLoggerPrivate() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.slf4j.Logger;
+            import org.slf4j.LoggerFactory;
+
+            class Test {
+                public static final Logger LOGGER = LoggerFactory.getLogger(Test.class);
+            }
+            """,
+            """
+            import org.slf4j.Logger;
+            import org.slf4j.LoggerFactory;
+
+            class Test {
+                private static final Logger LOGGER = LoggerFactory.getLogger(Test.class);
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void changePublicLog4j2LoggerPrivate() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.apache.logging.log4j.Logger;
+            import org.apache.logging.log4j.LogManager;
+
+            class Test {
+                public static final Logger LOGGER = LogManager.getLogger(Test.class);
+            }
+            """,
+            """
+            import org.apache.logging.log4j.Logger;
+            import org.apache.logging.log4j.LogManager;
+
+            class Test {
+                private static final Logger LOGGER = LogManager.getLogger(Test.class);
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void changeProtectedLog4jLoggerPrivate() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.apache.log4j.Logger;
+
+            class Test {
+                protected Logger log = Logger.getLogger(Test.class);
+            }
+            """,
+            """
+            import org.apache.log4j.Logger;
+
+            class Test {
+                private Logger log = Logger.getLogger(Test.class);
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void changeDefaultJulLoggerPrivate() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import java.util.logging.Logger;
+
+            class Test {
+                static final Logger LOG = Logger.getLogger(Test.class.getName());
+            }
+            """,
+            """
+            import java.util.logging.Logger;
+
+            class Test {
+                private static final Logger LOG = Logger.getLogger(Test.class.getName());
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void keepExistingPrivateLogger() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.slf4j.Logger;
+            import org.slf4j.LoggerFactory;
+
+            class Test {
+                private final Logger logger = LoggerFactory.getLogger(Test.class);
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void notALoggerField() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            class Test {
+                public String name = "test";
+                protected int count = 0;
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void loggerInInterfaceShouldNotChange() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.slf4j.Logger;
+            import org.slf4j.LoggerFactory;
+
+            interface Constants {
+                Logger logger = LoggerFactory.getLogger(Constants.class);
+            }
+            """
+          )
+        );
+    }
+
+    @Test
+    void localVariableLoggerShouldNotChange() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+            import org.slf4j.Logger;
+            import org.slf4j.LoggerFactory;
+
+            class Test {
+                public void doSomething() {
+                    Logger localLog = LoggerFactory.getLogger(Test.class);
+                    localLog.info("Hello");
+                }
+            }
+            """
+          )
+        );
+    }
+}