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Backstopper Sample Application - spring-boot3-webflux

Backstopper is a framework-agnostic API error handling and (optional) model validation solution for Java 17 and greater.

(NOTE: The Backstopper 1.x branch contains a version of Backstopper for Java 7+, and for the javax ecosystem. The current Backstopper supports Java 17+ and the jakarta ecosystem. The Backstopper 1.x releases also contain support for Spring 4 and 5, and Springboot 1 and 2.)

This submodule contains a sample application based on Spring Boot 3 + WebFlux (Netty) that fully integrates Backstopper.

  • Build the sample by running the ./buildSample.sh script.
  • Launch the sample by running the ./runSample.sh script. It will bind to port 8080 by default.
    • You can override the default port by passing in a system property to the run script, e.g. to bind to port 8181: ./runSample.sh -Dserver.port=8181

Things to try

All examples here assume the sample app is running on port 8080, so you would hit each path by going to http://localhost:8080/[endpoint-path]. It's recommended that you use a REST client like Postman for making the requests so you can easily specify HTTP method, payloads, headers, etc, and fully inspect the response.

Also note that all the following things to try are verified in a component test: VerifyExpectedErrorsAreReturnedComponentTest. If you prefer to experiment via code you can run, debug, and otherwise explore that test.

As you are doing the following you should check the logs that are output by the sample application and notice what is included in the log messages. In particular notice how you can search for an error_id that came from an error response and go directly to the relevant log message in the logs. Also notice how the ApiError.getName() value shows up in the logs for each error represented in a returned error contract (there can be more than one per request).

  • GET /sample - Returns the JSON serialization for the SampleModel model object. You can copy this into a POST call to experiment with triggering errors.
  • POST /sample with ContentType: application/json header - Using the JSON model retrieved by the GET call, you can trigger numerous different types of errors, all of which get caught by the Backstopper system and converted into the appropriate error contract.
    • Omit the foo field.
    • Set the value of the range_0_to_42 field to something outside of the allowed 0-42 range.
    • Set the value of the rgb_color field to something besides RED, GREEN, or BLUE, or omit it entirely. Note that the validation and deserialization of this enum field is done in a case insensitive manner - i.e. you can pass red, Green, or bLuE if you want and it will not throw an error.
    • Set two or more invalid values for foo, range_0_to_42, and rgb_color to invalid values all at once - notice you get back all relevant errors at once in the same error contract.
    • Set throw_manual_error to true to trigger a manual exception to be thrown inside the normal POST /sample endpoint.
      • Note the extra response headers that are included when you do this, and how they relate to the .withExtraResponseHeaders(...) method call on the builder of the exception that is thrown.
    • Pass in an empty JSON payload - you should receive a "Missing expected content" error back.
    • Pass in a junk payload that is not valid JSON - you should receive a "Malformed request" error back.
  • GET /sample/coreErrorWrapper - Triggers an error to be thrown that appears to the caller like a normal generic service exception, but the SOME_MEANINGFUL_ERROR_NAME name from the ApiError it represents shows up in the logs to help you disambiguate what the true cause was.
  • GET /sample/triggerUnhandledError - Triggers an error that is caught by the unhandled exception handler portion of Backstopper and converted to a generic service exception.
  • GET /sample/withRequiredQueryParam?requiredQueryParamValue=not-an-int - Triggers an error in the Spring Boot framework when it cannot coerce the query param value to the required type (an integer), which results in a Backstopper "Type conversion error".
  • GET /sample/withRequiredHeader with a requiredHeaderValue: not-an-int header - Similar to the query param example, this triggers an error in the Spring Boot framework when it cannot coerce the header value to the required type (an integer), which results in a Backstopper "Type conversion error".
  • GET /does-not-exist - Triggers a framework 404 which Backstopper handles.
  • DELETE /sample - Triggers a framework 405 which Backstopper handles.
  • GET /sample with Accept: application/octet-stream header - Triggers a framework 406 which Backstopper handles.
  • POST /sample with ContentType: text/plain - Triggers a framework 415 which Backstopper handles.
  • GET /sample/flux - Uses the Flux return type to return multiple SampleModel objects. No errors thrown here, just exercising Spring WebFlux features.
  • GET /sample/monoError - Shows the case of returning an exception in a Mono endpoint by explicitly using Mono.error(...) rather than throwing the exception. Backstopper still handles these.
  • GET /sample/fluxError - Shows the case of returning an exception in a Flux endpoint by explicitly using Flux.error(...) rather than throwing the exception. Backstopper still handles these.
  • GET /sample/fromRouterFunction - Uses the WebFlux RouterFunction to connect a path to a handling method, and returns a SampleModel.
  • GET /sample/fromRouterFunction with throw-handler-filter-function-exception: true header - Triggers an exception to be thrown from a HandlerFilterFunction that executes before the /sample/fromRouterFunction endpoint. Backstopper handles this.
  • GET /sample/fromRouterFunction with return-exception-in-handler-filter-function-mono: true header - Same as above, but the exception is returned in the Mono from the HandlerFilterFunction rather than thrown.
  • Any request with a throw-web-filter-exception: true header. This will trigger an exception to be thrown in a WebFlux WebFilter as early in the filter chain as possible. Backstopper handles this.
  • Any request with a return-exception-in-web-filter-mono: true header. Same as above, but the exception is returned in the Mono from the WebFilter rather than thrown.

More Info

See the base project README.md, User Guide, and Backstopper repository source code and javadocs for all further information.

License

Backstopper is released under the Apache License, Version 2.0