diff --git a/example/javalib/linting/3-palantirformat/build.mill b/example/javalib/linting/3-palantirformat/build.mill
new file mode 100644
index 00000000000..e5bd5915199
--- /dev/null
+++ b/example/javalib/linting/3-palantirformat/build.mill
@@ -0,0 +1,26 @@
+package build
+
+import mill._
+import mill.javalib.palantirformat._
+
+object `package` extends RootModule with PalantirFormatModule {
+}
+
+/** See Also: src/A.java */
+
+/** Usage
+
+> ./mill palantirformat --check                                         # check should fail initially
+...checking format in java sources ...
+...src/A.java
+error: ...palantirformat aborted due to format error(s) (or invalid plugin settings/palantirformat options)
+
+> ./mill palantirformat                                                 # format all Java source files
+...formatting java sources ...
+
+> ./mill palantirformat --check                                         # check should succeed now
+...checking format in java sources ...
+
+> ./mill mill.javalib.palantirformat.PalantirFormatModule/ __.sources   # alternatively, use external module to check/format
+...formatting java sources ...
+*/
diff --git a/example/javalib/linting/3-palantirformat/src/A.java b/example/javalib/linting/3-palantirformat/src/A.java
new file mode 100644
index 00000000000..2fd4b5675f7
--- /dev/null
+++ b/example/javalib/linting/3-palantirformat/src/A.java
@@ -0,0 +1,6 @@
+public class A {
+
+    public static void main(String[] args) {
+    System.out.println("hello"); // indentation should be fixed
+    }
+}
diff --git a/scalalib/src/mill/javalib/palantirformat/PalantirFormatModule.scala b/scalalib/src/mill/javalib/palantirformat/PalantirFormatModule.scala
new file mode 100644
index 00000000000..e52bb33268e
--- /dev/null
+++ b/scalalib/src/mill/javalib/palantirformat/PalantirFormatModule.scala
@@ -0,0 +1,190 @@
+package mill
+package javalib.palantirformat
+
+import mill.api.{Loose, PathRef}
+import mill.define.{Discover, ExternalModule}
+import mill.main.Tasks
+import mill.scalalib.{CoursierModule, DepSyntax, JavaModule}
+import mill.util.Jvm
+
+trait PalantirFormatBaseModule extends CoursierModule {
+
+  /**
+   * Classpath for running Palantir Java Format.
+   */
+  def palantirformatClasspath: T[Loose.Agg[PathRef]] = T {
+    defaultResolver().resolveDeps(
+      Agg(ivy"com.palantir.javaformat:palantir-java-format:${palantirformatVersion()}")
+    )
+  }
+
+  /**
+   * JVM arguments for running Palantir Java Format. Defaults to values prescribed in
+   * "[[https://github.com/palantir/palantir-java-format/issues/548 Broken on Java 16]]".
+   */
+  def palantirformatJvmArgs: T[Seq[String]] = T {
+    Seq(
+      "--add-exports",
+      "jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
+      "--add-exports",
+      "jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
+      "--add-exports",
+      "jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED",
+      "--add-exports",
+      "jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+      "--add-exports",
+      "jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED"
+    )
+  }
+
+  /**
+   * Path to options file for Palantir Java Format CLI. Defaults to `millSourcePath` `/` `palantirformat.options`.
+   */
+  def palantirformatOptions: T[PathRef] = Task.Source(
+    millSourcePath / "palantirformat.options"
+  )
+
+  /**
+   * Palantir Java Format version. Defaults to `2.50.0`.
+   */
+  def palantirformatVersion: T[String] = T {
+    "2.50.0"
+  }
+}
+
+/**
+ * Formats Java source files using [[https://github.com/palantir/palantir-java-format Palantir Java Format]].
+ */
+trait PalantirFormatModule extends JavaModule with PalantirFormatBaseModule {
+
+  /**
+   * Formats Java source files.
+   *
+   * @param check if an exception should be raised when formatting errors are found
+   *              - when set, files are not formatted
+   * @param sources list of file or folder path(s) to be processed
+   *                - path must be relative to [[millSourcePath]]
+   *                - when empty, all [[sources]] are processed
+   */
+  def palantirformat(
+      check: mainargs.Flag = mainargs.Flag(value = false),
+      sources: mainargs.Leftover[String]
+  ): Command[Unit] = Task.Command {
+
+    val _sources =
+      if (sources.value.isEmpty) this.sources()
+      else sources.value.iterator.map(rel => PathRef(millSourcePath / os.RelPath(rel)))
+
+    PalantirFormatModule.palantirAction(
+      _sources,
+      check.value,
+      palantirformatOptions(),
+      palantirformatClasspath(),
+      palantirformatJvmArgs()
+    )
+  }
+}
+object PalantirFormatModule extends ExternalModule with PalantirFormatBaseModule with TaskModule {
+
+  override def defaultCommandName(): String = "formatAll"
+
+  /**
+   * Formats Java source files.
+   *
+   * @param check if an exception should be raised when formatting errors are found
+   *              - when set, files are not formatted
+   * @param sources list of [[JavaModule]] sources to process
+   */
+  def formatAll(
+      check: mainargs.Flag = mainargs.Flag(value = false),
+      @mainargs.arg(positional = true) sources: Tasks[Seq[PathRef]]
+  ): Command[Unit] = Task.Command {
+
+    val _sources = T.sequence(sources.value)().iterator.flatten
+
+    palantirAction(
+      _sources,
+      check.value,
+      palantirformatOptions(),
+      palantirformatClasspath(),
+      palantirformatJvmArgs()
+    )
+  }
+
+  lazy val millDiscover: Discover = Discover[this.type]
+
+  private[palantirformat] def palantirAction(
+      sources: IterableOnce[PathRef],
+      check: Boolean,
+      options: PathRef,
+      classPath: Loose.Agg[PathRef],
+      jvmArgs: Seq[String]
+  )(implicit ctx: api.Ctx): Unit = {
+
+    if (check) {
+      ctx.log.info("checking format in java sources ...")
+    } else {
+      ctx.log.info("formatting java sources ...")
+    }
+
+    val mainArgs = palantirArgs(sources, check, options)
+
+    ctx.log.debug(s"running palantirformat with $mainArgs")
+
+    val exitCode = Jvm.callSubprocess(
+      mainClass = "com.palantir.javaformat.java.Main",
+      classPath = classPath.map(_.path),
+      jvmArgs = jvmArgs,
+      mainArgs = mainArgs,
+      workingDir = ctx.dest,
+      check = false
+    ).exitCode
+
+    if (check && exitCode != 0) {
+      ctx.log.error(
+        "palantirformat aborted due to format error(s) (or invalid plugin settings/palantirformat options)"
+      )
+      throw new RuntimeException(s"palantirformat exit($exitCode)")
+    }
+  }
+
+  private def palantirArgs(
+      sources: IterableOnce[PathRef],
+      check: Boolean,
+      options: PathRef
+  ): Seq[String] = {
+
+    val args = Seq.newBuilder[String]
+
+    // https://github.com/palantir/palantir-java-format/blob/dae9be4b84e2bd4d7ea346c6374fda47eee7118f/palantir-java-format/src/main/java/com/palantir/javaformat/java/CommandLineOptionsParser.java#L199
+    if (os.exists(options.path)) args += s"@${options.path}"
+
+    // https://github.com/palantir/palantir-java-format/blob/dae9be4b84e2bd4d7ea346c6374fda47eee7118f/palantir-java-format/src/main/java/com/palantir/javaformat/java/CommandLineOptions.java#L27
+    if (check) {
+      // do not overwrite files and exit(1) if formatting changes were detected
+      args += "--dry-run" += "--set-exit-if-changed"
+    } else {
+      // format in place
+      args += "--replace"
+    }
+
+    // https://github.com/palantir/palantir-java-format/blob/dae9be4b84e2bd4d7ea346c6374fda47eee7118f/palantir-java-format/src/main/java/com/palantir/javaformat/java/CommandLineOptionsParser.java#L49
+    args ++=
+      sources
+        .iterator
+        .map(_.path)
+        .flatMap(os.walk(_, includeTarget = true))
+        .filter(os.isFile)
+        .filter(_.ext == "java")
+        .map(_.toString())
+
+    args.result()
+  }
+
+  /**
+   * Path to options file for Palantir Java Format CLI at `T.workspace` `/` `palantirformat.options`.
+   */
+  override def palantirformatOptions: T[PathRef] = Task.Source(
+    T.workspace / "palantirformat.options"
+  )
+}
diff --git a/scalalib/test/resources/javalib/palantirformat/after/example/A.java b/scalalib/test/resources/javalib/palantirformat/after/example/A.java
new file mode 100644
index 00000000000..25ca05a73b8
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/after/example/A.java
@@ -0,0 +1,6 @@
+public class A {
+
+  public static void main(String[] args) {
+    System.out.println("hello"); // indentation should be fixed
+  }
+}
diff --git a/scalalib/test/resources/javalib/palantirformat/after/google/A.java b/scalalib/test/resources/javalib/palantirformat/after/google/A.java
new file mode 100644
index 00000000000..357d4d7d252
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/after/google/A.java
@@ -0,0 +1,76 @@
+package com.google.googlejavaformat.java.test;
+
+/**
+ * Tests for AbstractTypeDeclarations, AnnotationTypeDeclarations, AnnotationTypeMemberDeclarations,
+ * Annotations, AnonymousClassDeclarations, ArrayAccesses, ArrayCreations, ArrayInitializers,
+ * ArrayTypes, AssertStatements, and Assignments.
+ */
+class A {
+  public @interface X {
+    int x();
+
+    int y() default
+        1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+            + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1;
+  }
+
+  @X(x = 1)
+  private @interface Y {}
+
+  // TODO(jdd): Add annotation declaration with empty body.
+
+  @X(x = 1)
+  @Y
+  protected @interface Z {}
+
+  // TODO(jdd): Include type annotations once we can include a higher language level.
+
+  int[] array1 = new int[5];
+  int[] array2 = new int[] {
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
+    26, 27, 28, 29, 30, 31
+  };
+  int[] array3 = {
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
+    26, 27, 28, 29, 30, 31
+  };
+  int[][] array4 = {
+    {0, 1}, {2, 3}, {4, 5}, {6, 7}, {8, 9}, {10, 11}, {12, 13}, {14, 15}, {16, 17}, {18, 19},
+    {20, 21}, {22, 23}
+  };
+  int[][][] arrayWithLongName = new int
+      [0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+          + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+      [0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+          + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+      [];
+
+  A a1 = new A() {
+    int x = array1[
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+        + array2[
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+        + array3[
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+        + array4[0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0][
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0];
+  };
+
+  void f(int something) {
+    assert 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+        == 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1;
+    assert 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+            == 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+        : "that was certainly unexpected!";
+    arrayWithLongName[
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0] =
+        arrayWithLongName[
+            0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0];
+    something = 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2
+        + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2
+        + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2;
+  }
+}
diff --git a/scalalib/test/resources/javalib/palantirformat/after/google/A.scala b/scalalib/test/resources/javalib/palantirformat/after/google/A.scala
new file mode 100644
index 00000000000..51d5f93ec23
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/after/google/A.scala
@@ -0,0 +1,7 @@
+package com.google.googlejavaformat.java.test
+
+object A {
+
+// plugin should ignore non Java file
+// introduce a compile error to trigger failure in case this file is processed
+//}
\ No newline at end of file
diff --git a/scalalib/test/resources/javalib/palantirformat/after/palantir/Main.java b/scalalib/test/resources/javalib/palantirformat/after/palantir/Main.java
new file mode 100644
index 00000000000..f00d7632849
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/after/palantir/Main.java
@@ -0,0 +1,33 @@
+package a;
+
+// imports should be sorted
+// unsed imports should be removed
+import some.Configuration;
+import some.GradleException;
+import some.MavenPublication;
+import some.Project;
+import some.PublishingExtension;
+import some.VariantVersionMappingStrategy;
+
+public class Main {
+
+    private static void configureResolvedVersionsWithVersionMapping(Project project) {
+        project.getPluginManager().withPlugin("maven-publish", plugin -> {
+            project.getExtensions()
+                    .getByType(PublishingExtension.class)
+                    .getPublications()
+                    .withType(MavenPublication.class)
+                    .configureEach(publication -> publication.versionMapping(mapping -> {
+                        mapping.allVariants(VariantVersionMappingStrategy::fromResolutionResult);
+                    }));
+        });
+    }
+
+    private static GradleException notFound(String group, String name, Configuration configuration) {
+        String actual = configuration.getIncoming().getResolutionResult().getAllComponents().stream()
+                .map(ResolvedComponentResult::getModuleVersion)
+                .map(mvi -> String.format("\t- %s:%s:%s", mvi.getGroup(), mvi.getName(), mvi.getVersion()))
+                .collect(Collectors.joining("\n"));
+        // ...
+    }
+}
diff --git a/scalalib/test/resources/javalib/palantirformat/before/example/src/A.java b/scalalib/test/resources/javalib/palantirformat/before/example/src/A.java
new file mode 100644
index 00000000000..2fd4b5675f7
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/before/example/src/A.java
@@ -0,0 +1,6 @@
+public class A {
+
+    public static void main(String[] args) {
+    System.out.println("hello"); // indentation should be fixed
+    }
+}
diff --git a/scalalib/test/resources/javalib/palantirformat/before/google/src/A.java b/scalalib/test/resources/javalib/palantirformat/before/google/src/A.java
new file mode 100644
index 00000000000..afb17751f4d
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/before/google/src/A.java
@@ -0,0 +1,84 @@
+package com.google.googlejavaformat.java.test;
+
+/**
+ * Tests for AbstractTypeDeclarations, AnnotationTypeDeclarations, AnnotationTypeMemberDeclarations,
+ * Annotations, AnonymousClassDeclarations, ArrayAccesses, ArrayCreations, ArrayInitializers,
+ * ArrayTypes, AssertStatements, and Assignments.
+ */
+class A {
+    public @interface X {
+        int x();
+
+        int y() default
+                1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+                        + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1;
+    }
+
+    @X(x = 1)
+    private @interface Y {}
+
+    // TODO(jdd): Add annotation declaration with empty body.
+
+    @X(x = 1)
+    @Y
+    protected @interface Z {}
+
+    // TODO(jdd): Include type annotations once we can include a higher language level.
+
+    int[] array1 = new int[5];
+    int[] array2 =
+            new int[] {
+                    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
+                    24, 25, 26, 27, 28, 29, 30, 31
+            };
+    int[] array3 = {
+            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
+            26, 27, 28, 29, 30, 31
+    };
+    int[][] array4 = {
+            {0, 1}, {2, 3}, {4, 5}, {6, 7}, {8, 9}, {10, 11}, {12, 13}, {14, 15}, {16, 17}, {18, 19},
+            {20, 21}, {22, 23}
+    };
+    int[][][] arrayWithLongName =
+            new int
+                    [0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                    + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+                    [0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                    + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+                    [];
+
+    A a1 =
+            new A() {
+                int x =
+                        array1[
+                                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                                        + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+                                + array2[
+                                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                                        + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+                                + array3[
+                                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                                        + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0]
+                                + array4[
+                                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                                        + 0][
+                                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0
+                                        + 0];
+            };
+
+    void f(int something) {
+        assert 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+                == 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1;
+        assert 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+                == 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
+                : "that was certainly unexpected!";
+        arrayWithLongName[
+                0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0] =
+                arrayWithLongName[
+                        0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0];
+        something =
+                2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2
+                        + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2
+                        + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2;
+    }
+}
\ No newline at end of file
diff --git a/scalalib/test/resources/javalib/palantirformat/before/google/src/A.scala b/scalalib/test/resources/javalib/palantirformat/before/google/src/A.scala
new file mode 100644
index 00000000000..51d5f93ec23
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/before/google/src/A.scala
@@ -0,0 +1,7 @@
+package com.google.googlejavaformat.java.test
+
+object A {
+
+// plugin should ignore non Java file
+// introduce a compile error to trigger failure in case this file is processed
+//}
\ No newline at end of file
diff --git a/scalalib/test/resources/javalib/palantirformat/before/palantir/palantirformat.options b/scalalib/test/resources/javalib/palantirformat/before/palantir/palantirformat.options
new file mode 100644
index 00000000000..093eb2fcd66
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/before/palantir/palantirformat.options
@@ -0,0 +1 @@
+--palantir
diff --git a/scalalib/test/resources/javalib/palantirformat/before/palantir/src/Main.java b/scalalib/test/resources/javalib/palantirformat/before/palantir/src/Main.java
new file mode 100644
index 00000000000..dea44f31c08
--- /dev/null
+++ b/scalalib/test/resources/javalib/palantirformat/before/palantir/src/Main.java
@@ -0,0 +1,34 @@
+package a;
+
+// imports should be sorted
+// unsed imports should be removed
+import some.Configuration;
+import some.GradleException;
+import some.MavenPublication;
+import some.Project;
+import some.PublishingExtension;
+import some.VariantVersionMappingStrategy;
+
+public class Main {
+
+    private static void configureResolvedVersionsWithVersionMapping(Project project) {
+        project.getPluginManager().withPlugin("maven-publish", plugin -> {
+            project
+                    .getExtensions()
+                    .getByType(PublishingExtension.class)
+                    .getPublications()
+                    .withType(MavenPublication.class)
+                    .configureEach(publication -> publication.versionMapping(mapping -> {
+                        mapping.allVariants(VariantVersionMappingStrategy::fromResolutionResult);
+                    }));
+        });
+    }
+
+    private static GradleException notFound(String group, String name, Configuration configuration) {
+        String actual = configuration.getIncoming().getResolutionResult().getAllComponents().stream()
+                .map(ResolvedComponentResult::getModuleVersion)
+                .map(mvi -> String.format("\t- %s:%s:%s", mvi.getGroup(), mvi.getName(), mvi.getVersion()))
+                .collect(Collectors.joining("\n"));
+        // ...
+    }
+}
diff --git a/scalalib/test/src/mill/javalib/palantirformat/PalantirFormatModuleTest.scala b/scalalib/test/src/mill/javalib/palantirformat/PalantirFormatModuleTest.scala
new file mode 100644
index 00000000000..d76b078eadc
--- /dev/null
+++ b/scalalib/test/src/mill/javalib/palantirformat/PalantirFormatModuleTest.scala
@@ -0,0 +1,132 @@
+package mill
+package javalib.palantirformat
+
+import mill.main.Tasks
+import mill.scalalib.ScalaModule
+import mill.testkit.{TestBaseModule, UnitTester}
+import utest._
+
+object PalantirFormatModuleTest extends TestSuite {
+
+  def tests: Tests = Tests {
+
+    val (before, after) = {
+      val root = os.Path(sys.env("MILL_TEST_RESOURCE_FOLDER")) / "javalib" / "palantirformat"
+      (root / "before", root / "after")
+    }
+
+    test("palantirformat") {
+
+      assert(
+        checkState(
+          afterFormat(before / "google"),
+          after / "google"
+        ),
+        checkState(
+          afterFormat(before / "palantir"),
+          after / "palantir"
+        ),
+        checkState(
+          afterFormat(before / "palantir", sources = Seq("src/Main.java")),
+          after / "palantir"
+        )
+      )
+
+      intercept[RuntimeException](
+        afterFormat(before / "palantir", check = true)
+      )
+    }
+
+    test("formatAll") {
+
+      assert(
+        checkState(
+          afterFormatAll(before / "google"),
+          after / "google"
+        ),
+        checkState(
+          afterFormatAll(before / "palantir"),
+          after / "palantir"
+        )
+      )
+
+      intercept[RuntimeException](
+        afterFormatAll(before / "google", check = true)
+      )
+    }
+
+    test("example") {
+
+      intercept[RuntimeException](
+        afterFormat(before / "example", check = true)
+      )
+
+      assert(
+        checkState(
+          afterFormat(before / "example"),
+          after / "example"
+        )
+      )
+    }
+  }
+
+  def checkState(actualFiles: Seq[os.Path], expectedRoot: os.Path): Boolean = {
+    val expectedFiles = walkFiles(expectedRoot)
+    actualFiles.length == expectedFiles.length &&
+    actualFiles.iterator.zip(expectedFiles.iterator).forall {
+      case (actualFile, expectedFile) =>
+        val actual = os.read(actualFile)
+        val expected = os.read(expectedFile)
+        actual == expected
+    }
+  }
+
+  def afterFormat(
+      moduleRoot: os.Path,
+      version: String = "2.50.0",
+      check: Boolean = false,
+      sources: Seq[String] = Seq.empty
+  ): Seq[os.Path] = {
+
+    object module extends TestBaseModule with ScalaModule with PalantirFormatModule {
+      override def palantirformatVersion: T[String] = version
+      override def scalaVersion: T[String] = sys.props("MILL_SCALA_2_13_VERSION")
+    }
+
+    val eval = UnitTester(module, moduleRoot)
+
+    eval(module.palantirformat(mainargs.Flag(check), mainargs.Leftover(sources: _*))).fold(
+      {
+        case api.Result.Exception(cause, _) => throw cause
+        case failure => throw failure
+      },
+      { _ =>
+        val Right(sources) = eval(module.sources)
+
+        sources.value.flatMap(ref => walkFiles(ref.path))
+      }
+    )
+  }
+
+  def afterFormatAll(modulesRoot: os.Path, check: Boolean = false): Seq[os.Path] = {
+
+    object module extends TestBaseModule with ScalaModule {
+      override def scalaVersion: T[String] = sys.props("MILL_SCALA_2_13_VERSION")
+    }
+
+    val eval = UnitTester(module, modulesRoot)
+    eval(PalantirFormatModule.formatAll(mainargs.Flag(check), Tasks(Seq(module.sources)))).fold(
+      {
+        case api.Result.Exception(cause, _) => throw cause
+        case failure => throw failure
+      },
+      { _ =>
+        val Right(sources) = eval(module.sources)
+        sources.value.flatMap(ref => walkFiles(ref.path))
+      }
+    )
+  }
+
+  def walkFiles(root: os.Path): Seq[os.Path] =
+    os.walk(root).filter(os.isFile)
+}