{"id":109,"date":"2018-09-10T20:02:38","date_gmt":"2018-09-10T20:02:38","guid":{"rendered":"http:\/\/www.matez.de\/?p=109"},"modified":"2018-09-10T20:05:16","modified_gmt":"2018-09-10T20:05:16","slug":"response-validation-when-using-feign-as-http-client-wrapper","status":"publish","type":"post","link":"https:\/\/www.matez.de\/index.php\/2018\/09\/10\/response-validation-when-using-feign-as-http-client-wrapper\/","title":{"rendered":"Response validation when using Feign as http client wrapper"},"content":{"rendered":"

If you have the requirement of validating the response of a rest interface, a good opportunity in Java is to use the bean validation api and its annotations. On top, if you use OpenFeign<\/a> wrapper to define the client in your application, you can now assign those validation annotations directly to your interface.<\/p>\n

If you have already seen in my previous blogpost about Feign Outbound metrics<\/a>, I am trying to extend feign with some decorator classes to add missing functionality. metrics-feign<\/a> is a library, which can be used to report outbound-metrics out of any invocation to the feign wrapper.<\/p>\n

Now I created another library, which makes it possible to validate the response using bean validation api (JSR349). Its called feign-validation<\/a> and you can find it at github<\/a> or maven central<\/a>.<\/p>\n

The only thing you have to do after setting it up is to add annotations to the interface class you are using. Here is an example:<\/p>\n

interface GitHub {\r\n@RequestLine(\"GET \/repos\/{owner}\/{repo}\/contributors\")\r\n@Size(min = 1, max = 3)\r\n@Valid\r\nList contributors(@Param(\"owner\") String owner, @Param(\"repo\") String repo);\r\n\r\n}\r\n\r\nstatic class Contributor {\r\n@NotNull\r\n@Size(min = 10)\r\nString login;\r\nint contributions;\r\n}\r\n\r\npublic static void main(String... args) {\r\n\r\nValidator validator = Validation.buildDefaultValidatorFactory().getValidator();\r\n\r\nGitHub github = ExtendedFeign.builder(validator)\/\/\r\n.decoder(new GsonDecoder()).target(GitHub.class, \"https:\/\/api.github.com\");\r\n\r\n\/\/ Fetch and print a list of the contributors to this library.\r\ntry {\r\nList contributors = github.contributors(\"OpenFeign\", \"feign\");\r\nfor (Contributor contributor : contributors) {\r\nSystem.out.println(contributor.login + \" (\" + contributor.contributions + \")\");\r\n}\r\n} catch (ConstraintViolationException ex) {\r\nex.getConstraintViolations().forEach(System.out::println);\r\n}\r\n\r\n}<\/pre>\n
If you would run this class, you can see, that the response is being validated against the given annotations and all violations a printed to stdout.<\/p>\n