feat: allow overriding JarSate classloader (to enable cli) (#2427)

Author: nedtwigg

CHANGES.md

@@ -10,7 +10,9 @@ This document is intended for Spotless developers.
 We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (starting after version `1.27.0`).
 
 ## [Unreleased]
+### Added
 * Support for`clang-format` on maven-plugin ([#2406](https://github.com/diffplug/spotless/pull/2406))
+* Allow overriding classLoader for all `JarState`s to enable spotless-cli ([#2427](https://github.com/diffplug/spotless/pull/2427))
 
 ## [3.0.2] - 2025-01-14
 ### Fixed

lib/src/main/java/com/diffplug/spotless/JarState.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 DiffPlug
+ * Copyright 2016-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,11 @@
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import javax.annotation.Nullable;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * Grabs a jar and its dependencies from maven,
  * and makes it easy to access the collection in
@@ -37,6 +42,21 @@
  * catch changes in a SNAPSHOT version.
  */
 public final class JarState implements Serializable {
+
+private static final Logger logger = LoggerFactory.getLogger(JarState.class);
+
+// Let the classloader be overridden for tools using different approaches to classloading
+@Nullable
+private static ClassLoader forcedClassLoader = null;
+
+/** Overrides the classloader used by all JarStates. */
+public static void setForcedClassLoader(@Nullable ClassLoader forcedClassLoader) {
+if (!Objects.equals(JarState.forcedClassLoader, forcedClassLoader)) {
+logger.info("Overriding the forced classloader for JarState from {} to {}", JarState.forcedClassLoader, forcedClassLoader);
+}
+JarState.forcedClassLoader = forcedClassLoader;
+}
+
 /** A lazily evaluated JarState, which becomes a set of files when serialized. */
 public static class Promised implements Serializable {
 private static final long serialVersionUID = 1L;
@@ -125,26 +145,36 @@ URL[] jarUrls() {
 }
 
 /**
- * Returns a classloader containing the only jars in this JarState.
+ * Returns either a forcedClassloader ({@code JarState.setForcedClassLoader()}) or a classloader containing the only jars in this JarState.
  * Look-up of classes in the {@code org.slf4j} package
  * are not taken from the JarState, but instead redirected to the class loader of this class to enable
  * passthrough logging.
  * <br/>
  * The lifetime of the underlying cacheloader is controlled by {@link SpotlessCache}.
+ *
+ * @see com.diffplug.spotless.JarState#setForcedClassLoader(ClassLoader)
  */
 public ClassLoader getClassLoader() {
+if (forcedClassLoader != null) {
+return forcedClassLoader;
+}
 return SpotlessCache.instance().classloader(this);
 }
 
 /**
- * Returns a classloader containing the only jars in this JarState.
+ * Returns either a forcedClassloader ({@code JarState.setForcedClassLoader}) or a classloader containing the only jars in this JarState.
  * Look-up of classes in the {@code org.slf4j} package
  * are not taken from the JarState, but instead redirected to the class loader of this class to enable
  * passthrough logging.
  * <br/>
- * The lifetime of the underlying cacheloader is controlled by {@link SpotlessCache}.
+ * The lifetime of the underlying cacheloader is controlled by {@link SpotlessCache}
+ *
+ * @see com.diffplug.spotless.JarState#setForcedClassLoader(ClassLoader)
  */
 public ClassLoader getClassLoader(Serializable key) {
+if (forcedClassLoader != null) {
+return forcedClassLoader;
+}
 return SpotlessCache.instance().classloader(key, this);
 }
 }

lib/src/test/java/com/diffplug/spotless/JarStateTest.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2025 DiffPlug
+ *
+ * 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
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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 com.diffplug.spotless;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.net.URLClassLoader;
+import java.nio.file.Files;
+import java.util.stream.Collectors;
+
+import org.assertj.core.api.SoftAssertions;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class JarStateTest {
+
+@TempDir
+java.nio.file.Path tempDir;
+
+File a;
+
+File b;
+
+Provisioner provisioner = (withTransitives, deps) -> deps.stream().map(name -> name.equals("a") ? a : b).collect(Collectors.toSet());
+
+@BeforeEach
+void setUp() throws IOException {
+a = Files.createTempFile(tempDir, "a", ".class").toFile();
+Files.writeString(a.toPath(), "a");
+b = Files.createTempFile(tempDir, "b", ".class").toFile();
+Files.writeString(b.toPath(), "b");
+}
+
+@AfterEach
+void tearDown() {
+JarState.setForcedClassLoader(null);
+}
+
+@Test
+void itCreatesClassloaderWhenForcedClassLoaderNotSet() throws IOException {
+JarState state1 = JarState.from(a.getName(), provisioner);
+JarState state2 = JarState.from(b.getName(), provisioner);
+
+SoftAssertions.assertSoftly(softly -> {
+softly.assertThat(state1.getClassLoader()).isNotNull();
+softly.assertThat(state2.getClassLoader()).isNotNull();
+});
+}
+
+@Test
+void itReturnsForcedClassloaderIfSetNoMatterIfSetBeforeOrAfterCreation() throws IOException {
+JarState stateA = JarState.from(a.getName(), provisioner);
+ClassLoader forcedClassLoader = new URLClassLoader(new java.net.URL[0]);
+JarState.setForcedClassLoader(forcedClassLoader);
+JarState stateB = JarState.from(b.getName(), provisioner);
+
+SoftAssertions.assertSoftly(softly -> {
+softly.assertThat(stateA.getClassLoader()).isSameAs(forcedClassLoader);
+softly.assertThat(stateB.getClassLoader()).isSameAs(forcedClassLoader);
+});
+}
+
+@Test
+void itReturnsForcedClassloaderEvenWhenRountripSerialized() throws IOException, ClassNotFoundException {
+JarState stateA = JarState.from(a.getName(), provisioner);
+ClassLoader forcedClassLoader = new URLClassLoader(new java.net.URL[0]);
+JarState.setForcedClassLoader(forcedClassLoader);
+JarState stateB = JarState.from(b.getName(), provisioner);
+
+JarState stateARoundtripSerialized = roundtripSerialize(stateA);
+JarState stateBRoundtripSerialized = roundtripSerialize(stateB);
+
+SoftAssertions.assertSoftly(softly -> {
+softly.assertThat(stateARoundtripSerialized.getClassLoader()).isSameAs(forcedClassLoader);
+softly.assertThat(stateBRoundtripSerialized.getClassLoader()).isSameAs(forcedClassLoader);
+});
+}
+
+private JarState roundtripSerialize(JarState state) throws IOException, ClassNotFoundException {
+ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+try (ObjectOutputStream oOut = new ObjectOutputStream(outputStream)) {
+oOut.writeObject(state);
+}
+try (ObjectInputStream oIn = new ObjectInputStream(new java.io.ByteArrayInputStream(outputStream.toByteArray()))) {
+return (JarState) oIn.readObject();
+}
+}
+
+}