requirekt

Idiomatic kotlin preconditions for spring boot Restful API's

Express API preconditions idiomatically

With requireKt you can substitute existing if else blocks that handle controller validations with a require function that automatically throws an API error if a condition is not satisfied.

This library was designed primarily for doing parameter validation in methods and constructors.

@RestController
@RequestMapping(value = ["/api/v1/users"])
class UserController() {

    companion object ErrorCodes {
        const val INVALID_USERNAME = "invalid username"
        const val PASSWORDS_DO_NOT_MATCH = "passwords do not match"
    }

    @PostMapping(
        consumes = [MediaType.APPLICATION_JSON_VALUE],
        produces = [MediaType.APPLICATION_JSON_VALUE]
    )
    fun add(@Valid @RequestBody body: NewUserInputModel): ResponseEntity<Any> {
        require(UserNameValidator().isValid(body.username), HttpStatus.CONFLICT) { INVALID_USERNAME }
        require(body.password == body.confirmPassword, HttpStatus.CONFLICT) { PASSWORDS_DO_NOT_MATCH }
        ...
    }
}

Examples

Require that a message is parsed correctly, otherwise throw an API error.

Note: The default status code returned by this function isBAD_REQUEST.

require(MessageParser.parse(message) == true) {
   "Message is invalid"
}

{
   "errors":[
      {
         "status":400,
         "code":"",
         "message":"Message is invalid"
      }
   ]
}

Pass additional arguments

You can change the response by passing in additional arguments. Namely status which requires a parameter of type HttpStatus and code which is a String that represents the API error code.

Example:

Require that a user is authenticated, otherwise throw an API Error.

require(authenticated == true, status = HttpStatus.FORBIDDEN, code = "104") {
   "Access forbidden. You are not allowed to administrate categories."
}

This will return the following JSON error:

{
   "errors":[
      {
         "status":403,
         "code":"104",
         "message":"Access forbidden. You are not allowed to administrate categories."
      }
   ]
}

Custom Error Responses

requirekt supports custom error responses in JSON using the require(value: Boolean, vararg args: ArrayList<Any>) function.

To use this function add a custom error with the @ErrorResponse annotation and override the toJSON function from AbstractErrorResponse

Example:

@ErrorResponse
class CustomErrorViewModel(val status: Int = 0,
                           val code: String? = null,
                           val message: String? = null,
                           val type: String? = null): AbstractErrorResponse() {

    override fun toJSON(vararg args: ArrayList<Any>): String {
        status = fromArgsAsInt(0, args)
        code = fromArgsAsString(1, args)
        message = fromArgsAsString(2, args)
        type = fromArgsAsString(3, args)
        return super.toJSON()
    }
}

NOTE: fromArgsAsInt, fromArgsAsFloat and fromArgsAsString are convenience functions that help your custom error class get the required arguments passed to the JSON() function.

Call the require function and pass a boolean to validate and, your arguments wrapped in arrayListOf in the same order as the constructor of your custom error response class. If they are not in the same order and of the same type, require will fail to create the custom error response in JSON.

require(value = false,
    arrayListOf(
         HttpStatus.FORBIDDEN.value(),
         "104",
         "Access forbidden. You are not allowed to administrate categories.",
         "authentication"
    )
)

Also make sure requireKt can scan for custom error classes by adding @SpringBootApplication(scanBasePackages = ["YOUR_PACKAGE", "ao.co.nextbss.requirekt"]) to your spring boot application entry point:

    @Configuration
    @SpringBootApplication(scanBasePackages = ["YOUR_APPLICATION_PACKAGE", "ao.co.nextbss.requirekt"])
    class YourApplication
    fun main(args: Array<String>) {
        runApplication<YourApplication>(*args)
    }

The output would than be the following:

{
  "errors" : [ {
    "status" : 403,
    "code" : "104",
    "message" : "Access forbidden. You are not allowed to administrate categories.",
    "type" : "authentication"
  } ]
}

Usage

Download

To get a Git project into your build:

Step 1. Add the JitPack repository to your build file

maven

<repositories>
	<repository>
		<id>jitpack.io</id>
		<url>https://jitpack.io</url>
	</repository>
</repositories>

gradle

allprojects {
	repositories {
		...
		maven { url 'https://jitpack.io' }
	}
}

Step 2. Add the dependency

maven

<dependency>
	<groupId>com.github.nextbss</groupId>
	<artifactId>requirekt</artifactId>
	<version>1.1.0</version>
</dependency>

gradle

dependencies {
    implementation 'com.github.nextbss:requirekt:1.1.0'
}

License

The library is available as open source under the terms of the MIT License.