public abstract void filter(Metadata metadata) throws TikaException;
@Test
    public void testDefault() throws Exception {
        Metadata metadata = new Metadata();
        metadata.set("title", "title");
        metadata.set("author", "author");

        MetadataFilter defaultFilter = new DefaultMetadataFilter();
        defaultFilter.filter(metadata);

        assertEquals(2, metadata.names().length);
        assertEquals("title", metadata.get("title"));
        assertEquals("author", metadata.get("author"));
    }