JSON APIリクエスト時に例外が発生したら、常にJSONでレスポンスする

app/Http/Kernel.php

@@ -40,6 +40,7 @@ class Kernel extends HttpKernel
 
         'api' => [
             'throttle:60,1',
+            \App\Http\Middleware\EnforceJson::class,
             \Illuminate\Routing\Middleware\SubstituteBindings::class,
         ],
 

app/Http/Middleware/EnforceJson.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+
+/**
+ * Request headerに Accept: application/json を上書きする。APIエンドポイント用。
+ */
+class EnforceJson
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Closure  $next
+     * @return mixed
+     */
+    public function handle($request, Closure $next)
+    {
+        $request->headers->set('Accept', 'application/json');
+
+        return $next($request);
+    }
+}