Avoid IOExceptions in delete() when the cache dir is deleted externally.

src/main/java/com/jakewharton/disklrucache/Util.java

@@ -50,6 +50,9 @@ static String readFully(Reader reader) throws IOException {
    * could not be deleted, or if {@code dir} is not a readable directory.
    */
   static void deleteContents(File dir) throws IOException {
+    if (!dir.exists()) {
+      return;
+    }
     File[] files = dir.listFiles();
     if (files == null) {
       throw new IOException("not a readable directory: " + dir);

src/test/java/com/jakewharton/disklrucache/DiskLruCacheTest.java

@@ -21,6 +21,7 @@
 import java.io.FileReader;
 import java.io.FileWriter;
 import java.io.InputStream;
+import java.io.IOException;
 import java.io.Reader;
 import java.io.StringWriter;
 import java.io.Writer;
@@ -885,6 +886,42 @@ public final class DiskLruCacheTest {
     assertThat(cache.get("a")).isNull();
   }
 
+  @Test public void deleteAfterCacheDirectoryIsDeletedExternallyDoesNotThrow()
+      throws IOException {
+    FileUtils.deleteDirectory(cacheDir);
+    cache.delete();
+  }
+
+  @Test public void deleteWithNotReadableCacheDirectoryThowsIOException()
+      throws IOException {
+    try {
+      if (!cacheDir.setReadable(false)) {
+        fail("Unable to set writable on: " + cacheDir);
+      }
+      cache.delete();
+      fail("Expected delete to throw");
+    } catch (IOException e) {
+      // Expected.
+    } finally {
+       cacheDir.setReadable(true);
+    }
+  }
+
+  @Test public void deleteWithNotWritableCacheDirectoryThowsIOException()
+      throws IOException {
+    try {
+      if (!cacheDir.setWritable(false)) {
+        fail("Unable to set writable on: " + cacheDir);
+      }
+      cache.delete();
+      fail("Expected delete to throw");
+    } catch (IOException e) {
+      // Expected.
+    } finally {
+       cacheDir.setWritable(true);
+    }
+  }
+
   private void assertJournalEquals(String... expectedBodyLines) throws Exception {
     List<String> expectedLines = new ArrayList<String>();
     expectedLines.add(MAGIC);