If a :flash key is set on the response by the handler, a :flash key with
the same value will be set on the next request that shares the same session.
This is useful for small messages that persist across redirects.
(use 'ring.middleware.flash
'ring.middleware.params
'ring.middleware.session
'ring.util.response
'ring.adapter.jetty)
(defn save
[request]
(let [value (-> request :params :value)]
;; somehow save value
;; the :flash key on the response will be placed in the :session by wrap-flash
(assoc (redirect "/") :flash "Value is saved")))
(defn home
[request]
(let [uri (-> request :uri)]
(if (.startsWith uri "/save")
(save request)
;; before calling the home fn wrap-flash will move the :flash message from the :session to the request
(if-let [flash-message (-> request :flash)]
(response (str "Flash message found: " flash-message))
(response "No flash message found")))))
(def app (-> home wrap-flash wrap-session wrap-params))
(run-jetty app {:port 3000})
;; go to http://localhost:3000 and http://localhost:3000/save
Source
ring/middleware/flash.clj:4
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(defn wrap-flash
"If a :flash key is set on the response by the handler, a :flash key with
the same value will be set on the next request that shares the same session.
This is useful for small messages that persist across redirects."
[handler]
(fn [request]
(let [session (request :session)
flash (session :_flash)
session (dissoc session :_flash)
request (assoc request
:session session
:flash flash)
response (handler request)
session (if-let [flash (response :flash)]
(assoc (response :session) :_flash flash)
session)]
(assoc response :session session))))
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