Convert a cell value to a suitable type for Clojure and retrieve it, using POI.

cell_value.clj

(import [org.apache.poi.ss.usermodel Cell DateUtil FormulaError]))

(defmulti cell-value (fn [cell]
                       (let [type (.getCellType cell)]
                         (if (= type Cell/CELL_TYPE_FORMULA)
                           (.getCachedFormulaResultType cell)
                           type))))

(defmethod cell-value Cell/CELL_TYPE_STRING [cell]
  (.getStringCellValue cell))

(defmethod cell-value Cell/CELL_TYPE_BOOLEAN [cell]
  (.getBooleanCellValue cell))

(defmethod cell-value Cell/CELL_TYPE_NUMERIC [cell]
  (if (DateUtil/isCellDateFormatted cell)
    (.getDateCellValue cell)
    (.getNumericCellValue cell)))

(defmethod cell-value Cell/CELL_TYPE_ERROR [cell]
  (-> cell (.getErrorCellValue) (FormulaError/forInt)))

(defmethod cell-value Cell/CELL_TYPE_BLANK [cell] nil)