The bean function is a very useful Java interop feature that provides a
read-only view of a Java Bean as a Clojure map.
As it stands, the function performs introspection on the bean's class
whenever the function is called:
(defn bean
"Takes a Java object and returns a read-only implementation of the
map abstraction based upon its JavaBean properties."
{:added "1.0"}
[^Object x]
(let [c (. x (getClass))
pmap (reduce1 (fn [m ^java.beans.PropertyDescriptor pd]
(let [name (. pd (getName))
method (. pd (getReadMethod))]
(if (and method (zero? (alength (. method
(getParameterTypes)))))
(assoc m (keyword name) (fn []
(clojure.lang.Reflector/prepRet (.getPropertyType pd) (. method (invoke x
nil)))))
m)))
{}
(seq (.. java.beans.Introspector
(getBeanInfo c)
(getPropertyDescriptors))))
v (fn [k] ((pmap k)))
snapshot (fn []
(reduce1 (fn [m e]
(assoc m (key e) ((val e))))
{} (seq pmap)))]
(proxy [clojure.lang.APersistentMap]
[]
(containsKey [k] (contains? pmap k))
(entryAt [k] (when (contains? pmap k) (new clojure.lang.MapEntry k (v
k))))
(valAt ([k] (when (contains? pmap k) (v k)))
([k default] (if (contains? pmap k) (v k) default)))
(cons [m] (conj (snapshot) m))
(count [] (count pmap))
(assoc [k v] (assoc (snapshot) k v))
(without [k] (dissoc (snapshot) k))
(seq [] ((fn thisfn [plseq]
(lazy-seq
(when-let [pseq (seq plseq)]
(cons (new clojure.lang.MapEntry (first pseq) (v (first
pseq)))
(thisfn (rest pseq)))))) (keys pmap))))))
I propose to cache the pmap value for each class using JDK 7's
ClassValue<http://docs.oracle.com/javase/7/docs/api/>.
Here's a proposed implementation:
(def ^:private ^java.lang.ClassValue bean-class-value
(proxy [java.lang.ClassValue]
[]
(computeValue [c]
(reduce (fn [m ^java.beans.PropertyDescriptor pd]
(let [name (. pd (getName))
method (. pd (getReadMethod))
type (.getPropertyType pd)]
(if (and method (zero? (alength (. method
(getParameterTypes)))))
(assoc m (keyword name) (fn [x]
(clojure.lang.Reflector/prepRet type (. method (invoke x nil)))))
m)))
{}
(seq (.. java.beans.Introspector
(getBeanInfo c)
(getPropertyDescriptors)))))))
(defn bean
"Takes a Java object and returns a read-only implementation of the
map abstraction based upon its JavaBean properties."
{:added "1.0"}
[^Object x]
(let [c (. x (getClass))
pmap (.get bean-class-value c)
v (fn [k] ((pmap k) x))
snapshot (fn []
(reduce (fn [m e]
(assoc m (key e) ((val e) x)))
{} (seq pmap)))]
(proxy [clojure.lang.APersistentMap]
[]
(containsKey [k] (contains? pmap k))
(entryAt [k] (when (contains? pmap k) (new clojure.lang.MapEntry k (v
k))))
(valAt ([k] (when (contains? pmap k) (v k)))
([k default] (if (contains? pmap k) (v k) default)))
(cons [m] (conj (snapshot) m))
(count [] (count pmap))
(assoc [k v] (assoc (snapshot) k v))
(without [k] (dissoc (snapshot) k))
(seq [] ((fn thisfn [plseq]
(lazy-seq
(when-let [pseq (seq plseq)]
(cons (new clojure.lang.MapEntry (first pseq) (v (first
pseq)))
(thisfn (rest pseq)))))) (keys pmap))))))
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