code: public static Writable filterLine(File self, @ClosureParams(value = SimpleType.class, options = "java.lang.String") Closure closure) throws IOException {
          return IOGroovyMethods.filterLine(newReader(self), closure);
      }
docs: Filters the lines of a File and creates a Writable in return to
  stream the filtered lines.
  
  @param self    a File
  @param closure a closure which returns a boolean indicating to filter
  the line or not
  @return a Writable closure
  @throws IOException if <code>self</code> is not readable
  @see IOGroovyMethods#filterLine(java.io.Reader, groovy.lang.Closure)
  @since 1.0