(transaction-request :amount 10.00 :order-id "user42")

我知道我可以明确地做到这一点,如this question所示：

(defn transaction-request [& {:keys [amount order-id]}]
  (doto (TransactionRequest.)
    (.amount amount)
    (.orderId order-id)))

但是,对于许多类来说这是重复的,当参数是可选的时,它变得更加复杂.使用反射,可以更简洁地定义这些功能：

(defn set-obj-from-map [obj m]
  (doseq [[k v] m]
    (clojure.lang.Reflector/invokeInstanceMethod
      obj (name k) (into-array Object [v])))
  obj)

(defn transaction-request [& {:as m}]
  (set-obj-from-map (TransactionRequest.) m))

(defn transaction-options-request [tr & {:as m}]
  (set-obj-from-map (TransactionOptionsRequest. tr) m))

显然,如果可能,我想避免反思.我试图定义一个宏映射的set-obj从地图,但我的宏夫不够强大.这可能需要eval,如here所述.

有没有办法调用在运行时指定的Java方法,而不使用反射？

提前致谢！

更新解决方案：

根据Joost的建议,我能够使用类似的技术来解决问题.一个宏在编译时使用反射来识别类有哪些setter方法,然后在表中查找param,并用该值调用该方法.

这里是宏和一个例子：

; Find only setter methods that we care about
(defn find-methods [class-sym]
  (let [cls (eval class-sym)
        methods (.getMethods cls)
        to-sym #(symbol (.getName %))
        setter? #(and (= cls (.getReturnType %))
                      (= 1 (count (.getParameterTypes %))))]
    (map to-sym (filter setter? methods))))

; Convert a Java camelCase method name into a Clojure :key-word
(defn meth-to-kw [method-sym]
  (-> (str method-sym)
      (str/replace #"([A-Z])"
                   #(str "-" (.toLowerCase (second %))))
      (keyword)))

; Returns a function taking an instance of klass and a map of params
(defmacro builder [klass]
  (let [obj (gensym "obj-")
        m (gensym "map-")
        methods (find-methods klass)]
    `(fn [~obj ~m]
       ~@(map (fn [meth]
               `(if-let [v# (get ~m ~(meth-to-kw meth))] (. ~obj ~meth v#)))
              methods)
       ~obj)))

; Example usage
(defn transaction-request [& {:as params}]
  (-> (TransactionRequest.)
    ((builder TransactionRequest) params)
    ; some further use of the object
  ))