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< h1 id = "exception-handling-with-ring" > Exception Handling with Ring< / h1 >
< pre > < code class = "lang-clj" > [metosin/reitit-middleware < span class = "hljs-string" > " 0.4.2" < / span > ]
< / code > < / pre >
< p > Exceptions thrown in router creation can be < a href = "../basics/error_messages.html" > handled with custom exception handler< / a > . By default, exceptions thrown at runtime from a handler or a middleware are not caught by the < code > reitit.ring/ring-handler< / code > . A good practise is a have an top-level exception handler to log and format the errors for clients.< / p >
< pre > < code class = "lang-clj" > (< span class = "hljs-name" > require< / span > ' [reitit.ring.middleware.exception < span class = "hljs-symbol" > :as< / span > exception])
< / code > < / pre >
< h3 id = "exceptionexception-middleware" > < code > exception/exception-middleware< / code > < / h3 >
< p > A preconfigured middleware using < code > exception/default-handlers< / code > . Catches:< / p >
< ul >
< li > Request & response < a href = "coercion.html" > Coercion< / a > exceptions< / li >
< li > < a href = "https://github.com/metosin/muuntaja" target = "_blank" > Muuntaja< / a > decode exceptions< / li >
< li > Exceptions with < code > :type< / code > of < code > :reitit.ring/response< / code > , returning < code > :response< / code > key from < code > ex-data< / code > .< / li >
< li > Safely all other exceptions< / li >
< / ul >
< pre > < code class = "lang-clj" > (< span class = "hljs-name" > require< / span > ' [reitit.ring < span class = "hljs-symbol" > :as< / span > ring])
(< span class = "hljs-name" > < span class = "hljs-builtin-name" > def< / span > < / span > app
(< span class = "hljs-name" > ring/ring-handler< / span >
(< span class = "hljs-name" > ring/router< / span >
[< span class = "hljs-string" > " /fail" < / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > fn< / span > < / span > [_] (< span class = "hljs-name" > < span class = "hljs-builtin-name" > throw< / span > < / span > (< span class = "hljs-name" > Exception.< / span > < span class = "hljs-string" > " fail" < / span > )))]
{< span class = "hljs-symbol" > :data< / span > {< span class = "hljs-symbol" > :middleware< / span > [exception/exception-middleware]}})))
(< span class = "hljs-name" > app< / span > {< span class = "hljs-symbol" > :request-method< / span > < span class = "hljs-symbol" > :get< / span > , < span class = "hljs-symbol" > :uri< / span > < span class = "hljs-string" > " /fail" < / span > })
< span class = "hljs-comment" > ;{:status 500< / span >
< span class = "hljs-comment" > ; :body {:type " exception" < / span >
< span class = "hljs-comment" > ; :class " java.lang.Exception" }}< / span >
< / code > < / pre >
< h3 id = "exceptioncreate-exception-middleware" > < code > exception/create-exception-middleware< / code > < / h3 >
< p > Creates the exception-middleware with custom options. Takes a map of < code > identifier => exception request => response< / code > that is used to select the exception handler for the thrown/raised exception identifier. Exception identifier is either a < code > Keyword< / code > or a Exception Class.< / p >
< p > The following handlers are available by default:< / p >
< table >
< thead >
< tr >
< th > key< / th >
< th > description< / th >
< / tr >
< / thead >
< tbody >
< tr >
< td > < code > :reitit.ring/response< / code > < / td >
< td > value in ex-data key < code > :response< / code > will be returned< / td >
< / tr >
< tr >
< td > < code > :muuntaja/decode< / code > < / td >
< td > handle Muuntaja decoding exceptions< / td >
< / tr >
< tr >
< td > < code > :reitit.coercion/request-coercion< / code > < / td >
< td > request coercion errors (http 400 response)< / td >
< / tr >
< tr >
< td > < code > :reitit.coercion/response-coercion< / code > < / td >
< td > response coercion errors (http 500 response)< / td >
< / tr >
< tr >
< td > < code > ::exception/default< / code > < / td >
< td > a default exception handler if nothing else matched (default < code > exception/default-handler< / code > ).< / td >
< / tr >
< tr >
< td > < code > ::exception/wrap< / code > < / td >
< td > a 3-arity handler to wrap the actual handler < code > handler exception request => response< / code > (no default).< / td >
< / tr >
< / tbody >
< / table >
< p > The handler is selected from the options map by exception identifier in the following lookup order:< / p >
< p > 1) < code > :type< / code > of exception ex-data
2) Class of exception
3) < code > :type< / code > ancestors of exception ex-data
4) Super Classes of exception
5) The ::default handler< / p >
< pre > < code class = "lang-clj" > < span class = "hljs-comment" > ;; type hierarchy< / span >
(< span class = "hljs-name" > derive< / span > < span class = "hljs-symbol" > ::error< / span > < span class = "hljs-symbol" > ::exception< / span > )
(< span class = "hljs-name" > derive< / span > < span class = "hljs-symbol" > ::failure< / span > < span class = "hljs-symbol" > ::exception< / span > )
(< span class = "hljs-name" > derive< / span > < span class = "hljs-symbol" > ::horror< / span > < span class = "hljs-symbol" > ::exception< / span > )
(< span class = "hljs-name" > < span class = "hljs-builtin-name" > defn< / span > < / span > handler [message exception request]
{< span class = "hljs-symbol" > :status< / span > < span class = "hljs-number" > 500< / span >
< span class = "hljs-symbol" > :body< / span > {< span class = "hljs-symbol" > :message< / span > message
< span class = "hljs-symbol" > :exception< / span > (< span class = "hljs-name" > .getClass< / span > exception)
< span class = "hljs-symbol" > :data< / span > (< span class = "hljs-name" > ex-data< / span > exception)
< span class = "hljs-symbol" > :uri< / span > (< span class = "hljs-symbol" > :uri< / span > request)}})
(< span class = "hljs-name" > < span class = "hljs-builtin-name" > def< / span > < / span > exception-middleware
(< span class = "hljs-name" > exception/create-exception-middleware< / span >
(< span class = "hljs-name" > < span class = "hljs-builtin-name" > merge< / span > < / span >
exception/default-handlers
{< span class = "hljs-comment" > ;; ex-data with :type ::error< / span >
< span class = "hljs-symbol" > ::error< / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > partial< / span > < / span > handler < span class = "hljs-string" > " error" < / span > )
< span class = "hljs-comment" > ;; ex-data with ::exception or ::failure< / span >
< span class = "hljs-symbol" > ::exception< / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > partial< / span > < / span > handler < span class = "hljs-string" > " exception" < / span > )
< span class = "hljs-comment" > ;; SQLException and all it' s child classes< / span >
java.sql.SQLException (< span class = "hljs-name" > < span class = "hljs-builtin-name" > partial< / span > < / span > handler < span class = "hljs-string" > " sql-exception" < / span > )
< span class = "hljs-comment" > ;; override the default handler< / span >
< span class = "hljs-symbol" > ::exception/default< / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > partial< / span > < / span > handler < span class = "hljs-string" > " default" < / span > )
< span class = "hljs-comment" > ;; print stack-traces for all exceptions< / span >
< span class = "hljs-symbol" > ::exception/wrap< / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > fn< / span > < / span > [handler e request]
(< span class = "hljs-name" > println< / span > < span class = "hljs-string" > " ERROR" < / span > (< span class = "hljs-name" > pr-str< / span > (< span class = "hljs-symbol" > :uri< / span > request)))
(< span class = "hljs-name" > handler< / span > e request))})))
(< span class = "hljs-name" > < span class = "hljs-builtin-name" > def< / span > < / span > app
(< span class = "hljs-name" > ring/ring-handler< / span >
(< span class = "hljs-name" > ring/router< / span >
[< span class = "hljs-string" > " /fail" < / span > (< span class = "hljs-name" > < span class = "hljs-builtin-name" > fn< / span > < / span > [_] (< span class = "hljs-name" > < span class = "hljs-builtin-name" > throw< / span > < / span > (< span class = "hljs-name" > ex-info< / span > < span class = "hljs-string" > " fail" < / span > {< span class = "hljs-symbol" > :type< / span > < span class = "hljs-symbol" > ::failue< / span > })))]
{< span class = "hljs-symbol" > :data< / span > {< span class = "hljs-symbol" > :middleware< / span > [exception-middleware]}})))
(< span class = "hljs-name" > app< / span > {< span class = "hljs-symbol" > :request-method< / span > < span class = "hljs-symbol" > :get< / span > , < span class = "hljs-symbol" > :uri< / span > < span class = "hljs-string" > " /fail" < / span > })
< span class = "hljs-comment" > ; ERROR " /fail" < / span >
< span class = "hljs-comment" > ; => {:status 500,< / span >
< span class = "hljs-comment" > ; :body {:message " default" < / span >
< span class = "hljs-comment" > ; :exception clojure.lang.ExceptionInfo< / span >
< span class = "hljs-comment" > ; :data {:type :user/failue}< / span >
< span class = "hljs-comment" > ; :uri " /fail" }}< / span >
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