public InputStream extractRevision ( String field ) throws IOException { getSignatureNames ( ) ; field = getTranslatedFieldName ( field ) ; if ( ! sigNames . containsKey ( field ) ) return null ; int length = ( ( int [ ] ) sigNames . get ( field ) ) [ 0 ] ; RandomAccessFileOrArray raf = reader . getSafeFile ( ) ; raf . reOpen ( ) ; raf . seek ( 0 ) ; return new RevisionStream ( raf , length ) ; }
Extracts a revision from the document .