[IO-874] FileUtils.forceDelete can delete a broken symlink again (#756)

* [IO-874] FileUtils.forceDelete can delete a broken symlink again.

* [IO-874] fix checkstyle error

Author: JoergBudi

src/main/java/org/apache/commons/io/FileUtils.java

@@ -294,7 +294,7 @@ public static String byteCountToDisplaySize(final Number size) {
      */
     private static void checkExists(final File file, final boolean strict) throws FileNotFoundException {
         Objects.requireNonNull(file, PROTOCOL_FILE);
-        if (strict && !file.exists()) {
+        if (strict && !file.exists() && !isSymlink(file)) {
             throw new FileNotFoundException(file.toString());
         }
     }

src/test/java/org/apache/commons/io/FileUtilsTest.java

@@ -1761,6 +1761,42 @@ void testForceDeleteUnwritableFile() throws Exception {
         }
     }
 
+    @Test
+    public void testForceDeleteBrokenSymlink() throws Exception {
+        final ImmutablePair<Path, Path> pair = createTempSymbolicLinkedRelativeDir();
+        final Path symlinkedDir = pair.getLeft();
+        final Path targetDir = pair.getRight();
+
+        Files.delete(targetDir);
+        assertFalse(Files.exists(symlinkedDir));
+        assertTrue(Files.isSymbolicLink(symlinkedDir));
+
+        FileUtils.forceDelete(symlinkedDir.toFile());
+
+        // check targeted symlink is gone
+        assertFalse(Files.exists(symlinkedDir));
+        assertFalse(Files.isSymbolicLink(symlinkedDir));
+    }
+
+    @Test
+    public void testForceDeleteSymlink() throws Exception {
+        final ImmutablePair<Path, Path> pair = createTempSymbolicLinkedRelativeDir();
+        final Path symlinkedDir = pair.getLeft();
+        final Path targetDir = pair.getRight();
+
+        assertTrue(Files.exists(symlinkedDir));
+        assertTrue(Files.isSymbolicLink(symlinkedDir));
+        assertTrue(Files.exists(targetDir));
+
+        FileUtils.forceDelete(symlinkedDir.toFile());
+
+        // check targeted symlink is gone
+        assertFalse(Files.exists(symlinkedDir));
+        assertFalse(Files.isSymbolicLink(symlinkedDir));
+        // dir targeted by symlink is not deleted
+        assertTrue(Files.exists(targetDir));
+    }
+
     @Test
     void testForceMkdir() throws Exception {
         // Tests with existing directory