Cannot delete file even after closing InputStream

After reading a file, I'm trying to delete it, but the following error appears:

java.io.IOException: Unable to delete file test.zip at org.apache.commons.io.FileUtils.forceDelete (FileUtils.java:1390) at org.apache.commons.io.FileUtils.cleanDirectory (FileUtils.java:1044) at org.apache.commons.io.FileUtils.deleteDirectory (FileUtils.java:977)

Here is my code. I've been careful to close the InputStream in the finally clause and only then call the method that deletes the file, but even then I can only delete it when I stop the program.

 InputStream is = null;
 try {
     is = new URL(filePath).openStream(); // filePath is a string containing the path to the file like http://test.com/file.zip
     BufferedReader reader = new BufferedReader(new InputStreamReader(is, "utf-8"));
     String line;
     StringBuilder sb = new StringBuilder();

     while ((line = reader.readLine()) != null) {
         sb.append(line.trim());
     }

     String xml = sb.toString(); // this code is working, the result of the "xml" variable is as expected
  } catch (Exception e) {
      e.printStackTrace();
  } finally {
      try {
          if (is != null) {
              is.close();
          }
      } catch (Exception e) {
          e.printStackTrace();
      }

      removeFileAndFolder(absolutePath);
  }


private void removeFileAndFolder(String absolutePath) {
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                String folder = getFolder(absolutePath); // this method just get the path to the folder, because I want to delete the entire folder, but the error occurs when deleting the file
                FileUtils.deleteDirectory(new File(folder));

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
}

After some tests I discovered that I can manually delete the file just before the line "is = new URL (filePath) .openStream ();". After it, and even after the line "is.close ();" I can not delete the file manually unless I stop the program.