> For the complete documentation index, see [llms.txt](https://kelby.gitbook.io/rails-beginner-s-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kelby.gitbook.io/rails-beginner-s-guide/actiondispatch_middleware/each_middleware/middleware_show_exceptions.md).

# Show Exceptions

程序抛异常时，用什么程序来处理。

它只是接口，它关心的是用什么，而不是如何处理。(因为不是它处理的！) 对内调用 Exception Wrapper 对外调用 Public Exceptions.

```ruby
# 对内
wrapper = ExceptionWrapper.new(env, exception)
```

```ruby
# 对外
config.exceptions_app || ActionDispatch::PublicExceptions.new(Rails.public_path)
response = @exceptions_app.call(env)
```