JUnit Rule for managing the Spring Current Request

Sometimes in your code, you have a need to work with the Current Request. One good example of this - that I do a lot - is generating URLs. You don't always know where the application is deployed, and it might even be available on multiple addresses. Configuring the deployment URL into the application is not always easy, but Spring has some very useful utilities for this. (

 and

 ```MvcUriComponentsBuilder```

). These are powered off of the current request, which is itself stored in a utility called

 ```RequestContextHolder```

.

When you've written some code to use this, you invariably want to then test it. And that's fine, but setting up the

 ```RequestContetxHolder```

 in a test isn't always as trivial as it should be. You end up using a

 ```MockHttpServletRequest```

 and needing to dig into how this needs to be set up correctly - which parts of the "Current URI" go into which fields. And because I find myself doing this over and over, I've put together a JUnit rule to do it for me. Here it is. Note, it's written in Kotlin because that's my preference, but it would be trivial to translate.



```kotlin
import org.junit.rules.TestRule
import org.junit.runner.Description
import org.junit.runners.model.Statement
import org.slf4j.LoggerFactory
import org.springframework.mock.web.MockHttpServletRequest
import org.springframework.web.context.request.RequestContextHolder
import org.springframework.web.context.request.ServletRequestAttributes
import org.springframework.web.util.UriComponentsBuilder

/**
 * JUnit Rule to set up the current request context
 * @property uri The URI to act as the current request
 */
class CurrentRequestRule(private val uri: String) : TestRule {
    companion object {
        /** The logger to use */
        private val LOG = LoggerFactory.getLogger(CurrentRequestRule::class.java)
    }

    /** The request that we are claiming is current */
    private val request: MockHttpServletRequest

    init {
        val uriComponents = UriComponentsBuilder.fromUriString(uri).build()
        request = MockHttpServletRequest("GET", uriComponents.path)
        request.scheme = uriComponents.scheme
        request.serverName = uriComponents.host
        request.serverPort = uriComponents.port
        request.queryString = uriComponents.query
    }
    /**
     * Ensure that the Spring [RequestContextHolder] contains a request for the "Current URI" for the duration of the test
     * @param base The [Statement] to be modified
     *
     * @param description A [Description] of the test implemented in `base`. Not used.
     *
     * @return a new statement which sets up the RequestContextHolder before the `base` statement is called, and clears
     * it aftereards
     */
    override fun apply(base: Statement, description: Description): Statement {
        return object : Statement() {
            override fun evaluate() {
                LOG.debug("Setting current URI to {}", uri)
                val requestAttributes = ServletRequestAttributes(request)
                try {
                    RequestContextHolder.setRequestAttributes(requestAttributes)
                    base.evaluate()
                } finally {
                    RequestContextHolder.resetRequestAttributes()
                    LOG.debug("Clearing current URI")
                }
            }

        }
    }
}

Feel free to take it, use it in your code, do what you want with it. You don't even need to credit me - though I won't object if you do ;)

I'm curious what other useful JUnit Rules like this people have for their projects now. :)