using reified types to extract param, header and body. (#816)

* using reified types to extract param, header and body.

* Added some examples.

Author: vjames19

modules/jooby-lang-kotlin/src/main/kotlin/org/jooby/Jooby.kt

@@ -305,14 +305,26 @@ val Mutant.doubleValue: Double
 val Mutant.value: String
   get() = value()
 
+inline fun <reified T> Mutant.to(): T {
+  return this.to(T::class.java)
+}
+
 fun <T:Any> Mutant.to(type: KClass<T>): T {
   return this.to(type.java)
 }
 
+inline fun <reified T> Mutant.to(contentType: MediaType): T {
+  return this.to(T::class.java, contentType)
+}
+
 fun <T:Any> Mutant.to(type: KClass<T>, contentType: MediaType): T {
   return this.to(type.java, contentType)
 }
 
+inline fun <reified T> Mutant.to(contentType: String): T {
+  return this.to(T::class.java, contentType)
+}
+
 fun <T:Any> Mutant.to(type: KClass<T>, contentType: String): T {
   return this.to(type.java, contentType)
 }
@@ -341,3 +353,15 @@ fun <T:Comparable<T>> Mutant.toSortedSet(type: KClass<T>): SortedSet<T> {
 fun <T:Any> Request.set(type: KClass<T>, value: Any): Request {
   return this.set(type.java, value)
 }
+
+inline fun <reified T> Request.param(name: String): T {
+  return param(name).to(T::class.java)
+}
+
+inline fun <reified T> Request.header(name: String): T {
+  return param(name).to(T::class.java)
+}
+
+inline fun <reified T> Request.body(): T {
+  return body().to(T::class.java)
+}

modules/jooby-lang-kotlin/src/test/kotlin/examples/kotlin/Fn.kt

@@ -39,5 +39,22 @@ fun main(args: Array<String>) {
         chain.next(req, rsp)
       }
     }.name("pets")
+
+    get("/params") {
+      val name = param<String>("name")
+      val age = param<Int>("age")
+      "Hi $name, your username is now ${name + age}"
+    }
+
+    get("/headers") {
+      val name = header<String>("name")
+      val age = header<Int>("age")
+      "Hi $name, your username is now ${name + age}"
+    }
+
+    get("/body") {
+      val user = body<User>()
+      user
+    }
   }
 }