core/src/main/java/com/digitalpebble/stormcrawler/util/MetadataTransfer.java
public Metadata filter(Metadata metadata) {
        Metadata filtered_md = _filter(metadata, mdToTransfer);

        // add the features that are only persisted but
        // not transfered like __redirTo_
        filtered_md.putAll(_filter(metadata, mdToPersistOnly));

        return filtered_md;
    }
public Metadata filter(Metadata metadata) {
        Metadata filtered_md = _filter(metadata, mdToTransfer);

        // add the features that are only persisted but
        // not transfered like __redirTo_
        filtered_md.putAll(_filter(metadata, mdToPersistOnly));

        return filtered_md;
    }
Determine which metadata should be persisted for a given document
including those which are not necessarily transferred to the outlinks