public abstract void filter(Metadata metadata) throws TikaException;
@Test
    public void testFieldNameMapping() throws Exception {
        TikaConfig config = getConfig("TIKA-3137-field-mapping.xml");

        Metadata metadata = new Metadata();
        metadata.set(TikaCoreProperties.TIKA_CONTENT, "quick brown fox");
        metadata.set("author", "author");
        metadata.set("a", "a-value");

        MetadataFilter filter = config.getMetadataFilter();
        filter.filter(metadata);
        assertEquals("quick brown fox", metadata.get("content"));
        assertEquals("a-value", metadata.get("b"));
        assertNull(metadata.get("author"));
        assertNull(metadata.get("a"));
    }