Building APIs with Kotlin and SparkBy Travis Spencer(@travisspencer)

Intro & Agenda

•Why Kotlin• Some basics of the syntax•Quick intro to Spark•Using Kotlin & Spark together

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Why Kotlin

• Compiles to JVM bytecode and JavaScript• From industry not academia•Open source & costs nothing to adopt• Can use existing Java or JavaScript frameworks• Very low learning curve

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Why Kotlin

• Supports OO and functional programming styles• Excellent IDE support (Intellij and Eclipse)• Perfect for Java & Android shops• Strong commercial support from

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• fun keyword

Basic Syntax

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• fun keyword• Return type (Unit default)

Basic Syntax

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• fun keyword• Return type (Unit default)• Types of args after names

Basic Syntax

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• fun keyword• Return type (Unit default)• Types of args after names

Basic Syntax

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•Named arguments

• fun keyword• Return type (Unit default)• Types of args after names

Basic Syntax

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•Named arguments• Single expression functions

Passing Function Literals

Call like this… …instead of this!

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• Allows you to pass any type that inherits from Controllable• Safely upcast at run-time

Declaration-site Variance

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• Variables must be declared as nullable •Null checks are required at compile time

Nullability Must be Explicit

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Data Classes

• equals • hashCode • toString

• copy•Getters and setters

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Multiple Return Values

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Overridable Methods

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Overriding Open Methods

•Override

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Controller Overloads

•Override•Named arguments (again)

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Controller Overloads

•Override•Named arguments (again)

• mapOf standard function

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Controller Overloads

•Override•Named arguments (again)

• mapOf standard function• to keyword to nicely define associative array

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Smartcasts

Is of type Any!

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Smartcasts

is operator checks if type is ControllerResultat run-time

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Smartcasts

ControllerResultproperties are available after logical AND

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Ranges

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String Interpolation

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Multi-line Strings

val l = b?.length() ?: -1

Elvis Operator

Extension Functions

Adds foo() to all strings

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And of course equality is done right!

Equals

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• Conversion tools built into Intellij & Eclipse •Maven, Ant, Gradle•Docs with Javadoc and Markdown•…and

Tools

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A Debugger!

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Using Kotlin with Spark

Intro to Spark

• Tiny framework for setting up routes•No XML config•No annotations• Starts a Web server automatically• sparkjava.com

Hello World

Then hit http://localhost:4567/hello

Request & Response Classes

Request & Response objects have lots of useful methods

Aborting Requests

Parameterized URL Patterns

http://localhost:4567/users/bob

bob == :name parameter defined in route

Templatized Responses

Building a Robust API with SparkControllers, Dependency Injection, etc.

Code Walkthrough

• Intro to Spark - http://goo.gl/oPm0jV • Kotlin + Spark blog post • Part 1 - http://goo.gl/WlxKQq • Part 2 - http://goo.gl/cE0gxz

• Source code - http://goo.gl/x1CVuc

Links to More Info