Pro Kotlin Web Apps from Scratch

Table of Contents....5 About the Author....15 About the Technical Reviewer....16 Acknowledgments....17 Introduction....18 Chapter 1: Setting Up a Development Environment....19 Get Started with IntelliJ IDEA Community Edition....19 Download and Run IntelliJ IDEA....20 Create a New Kotlin Project with IntelliJ IDEA....20 Kotlin Hello, World!....25 Kotlin Naming Conventions....25 Write Some Code....25 Run Your Code with IntelliJ IDEA....27 Run Your Code with Gradle....28 IntelliJ IDEA Tips and Tricks....29 Look Out for the Progress Bar....30 Remember to Refresh the Gradle Project in IntelliJ IDEA....31 Embrace Auto-completion in IntelliJ IDEA....32 Chapter 2: Setting Up the Web App Skeleton....34 Web Server Hello, World!....35 Choosing Ktor....35 Add the Ktor Library....35 Start a Web Server....36 Extracting to a Separate Function....37 Using Lambdas....38 Named Arguments Instead of Magic Numbers and Booleans....39 Run Your Web App....40 Logging....41 Loggers on the Java Platform....41 Configure Logging in Your Web App....42 Write to the Log from Your Own Code....45 A Note on “Magic” XML Config Files....47 Useful Error Pages....48 Chapter 3: Configuration Files....51 Create a Configuration File....52 The Configuration File Anatomy....52 Reading Values from Your Configuration File....53 Make the Configuration Fail Early and Type-Safe....54 Store Configuration in a Data Class....55 Load Config into the Data Class....56 Kotlin Null Safety....56 Kotlin Platform Types....57 Use the Data Class in Your Web App....58 Use let Blocks to Avoid Intermediate Variables....59 Provide Different Default Values for Different Environments....60 Environment-Specific Config Files....60 Define the Web App Environment....61 Override Defaults with Environment-Specific Config....61 Secret Config Values....62 Don’t Store Secrets in Version Control....62 Logging Config on Web App Startup....65 Format the Output....66 Masking Secrets....66 Writing to the Log....67 Chapter 4: Decoupling Web Handlers from Specific Libraries....69 Your Own HTTP Response Abstraction....70 Representing HTTP Responses....70 Multiple Response Types....71 Convenience Functions for Headers....73 Case-Insensitive Headers....78 The fold Function....79 Destructuring Assignment....80 Connecting to Ktor....81 Ktor Route Mapping....81 Extension Functions....82 Functions Returning Functions....83 Map Headers....84 Map TextWebResponse and Status Code....85 Map JsonWebResponse....86 Using the New Mapping....88 A Note on Overengineering....89 Chapter 5: Connecting to and Migrating SQL Databases....91 Connecting to a SQL Database....92 The Connection Pool....92 Installing the Database Driver....93 Setting Up H2....94 Updating WebappConfig....94 Set Up the Connection Pool....96 Creating a Connection....97 The Initial Schema....98 Installing Flyway....98 Running Flyway During Startup....98 Creating the Initial Schema....100 Managing Schema Changes....101 Don’t Edit Migrations After Run....101 Adding More Schema....102 Adding Non-nullable Columns....102 Backward-Compatible Migrations....104 Insert Seed Data....105 Repeatable Migrations....105 Updating Repeatable Migrations....106 Handling Failed Migrations....107 Failed Migrations Locally....107 Failed Migrations in Production....107 Rerunning Failed Migration....108 Manually Performing Migration....108 Chapter 6: Querying a SQL Database....109 Setting Up Querying....109 Use SQL Directly....110 Installing Kotliquery....111 Mapping Query Results....111 Execute SQL Queries....112 Creating a Session....112 Querying for Single Rows....113 Querying for Multiple Rows....113 Inserting Rows....115 Updating and Deleting....116 Positional vs. Named Parameters....116 Additional Operations....117 Querying from Web Handlers....117 Creating a Helper Function....117 A Note on Architecture....119 Avoid Long-Running Connections....119 Maps vs. Data Classes....120 Passing Around Maps....120 Passing Individual Properties....121 Mapping to a Data Class....122 Database Transactions....125 Creating Transactions....125 Transactions in Web Handlers....126 Type-Safe Transactional Business Logic....127 Nested Transactions....128 Chapter 7: Automated Tests with jUnit 5....130 Setting Up Your Environment....130 Adding jUnit 5 and kotlin.test....131 Writing a Failing Test....132 Running a Failing Test....132 Making the Test Pass....134 Writing Web App Tests....136 Setting Up the Basics....136 Writing a Failing Test....137 Making the Test Pass....139 Avoiding Leaky Tests....140 Leaky Tests....140 Avoiding Leaks with Transactions....141 Avoiding Leaks with Relative Asserts....144 Test-Driven Development....146 Design and Verification....146 Writing a Failing Test....146 Making the Test Pass....148 Notes on Methodology....148 What About Front-End Tests?....148 Real Database Writes vs. Mocks....149 Unit vs. Integration Tests....150 Chapter 8: Parallelizing Service Calls with Coroutines....151 Preparing Your Web App....151 Implementing a Fake Service....152 Adding a Second Server....152 Understanding Coroutines....154 The delay Coroutine....154 The Problem with Threads....154 Suspending Instead of Locking....155 Coroutine Contexts....155 Coroutines in Ktor....157 Parallelizing Service Calls....158 Adding Dependencies....158 Performing Parallelized Calls....159 Handling Race Conditions....161 Adding to Ktor....161 Mixing Coroutines and Blocking Calls....162 Wrapping Blocking Calls....162 Coroutine Internals....163 Kotlin vs. KotlinX....163 Comparing with Arrow....164 Using Low-Level Continuations....167 Java Platform Implementation Details....168 Chapter 9: Building Traditional Web Apps with HTML and CSS....171 Patterns and Organization....172 Generating HTML....172 Using the kotlinx.html DSL....172 Using the Ktor HTML DSL....173 The Power of the DSL....174 Operator Overloading....175 Adding Custom Tags....176 CSS and Assets....177 Serving Static Files....177 Instant Reloading....180 Reusable Layouts....181 Adding a Layout....182 Using the Layout....183 Adding WebResponse for HTML....184 Implementing HtmlWebResponse....184 Extension Function Precedence....185 Responding with HtmlWebResponse....186 A Note on Abstractions....188 User Security....188 Password Hashing....188 Using Bcrypt for Hashing....189 Updating Your Migrations....192 Adding a Login Form....193 Wiring Up Your Web App....193 Different Types of Sessions....195 Adding a New Ktor Extension Function....196 Configuring Session Cookies....197 Logging In....199 Protecting Routes with Authentication....201 Logging Out....204 Chapter 10: Building API-Based Back Ends....206 Handling API Calls....206 Parsing Input....206 Validating and Extracting Input....207 Avoid Automatic Serialization....209 Internal vs. External APIs....211 Single-Page Apps....211 Hosting Alongside API....211 Hosting Separately with CORS....213 Authenticating Users....215 Native Apps....216 Using Cookies for Authentication....216 Using JWTs for Authentication....216 Performing Authentication....220 Chapter 11: Deploying to Traditional Server Based Environments....222 Packaging as Self-Contained JAR Files....222 What’s a JAR File....222 Self-Contained JAR Files....223 Packaging with Gradle....224 Building the JAR File....224 Executing the JAR File....225 Packaging for Production....226 Building Docker Images....226 Running Docker Images Locally....228 Deploying to Production....229 Chapter 12: Building and Deploying to Serverless Environments....231 Detaching Your Code....232 Separating Handlers from Ktor....232 Basic Structure....233 Detached Web Handlers....235 Run Web Handlers on AWS Lambda....235 Making AWS Lambda Web Handlers....235 Deploying to AWS Lambda....237 Calling Your Existing Handlers....245 Improving Performance....251 Performance and Cold Starts....252 Initialization Time vs. Execution Time....252 Lazy Loading....253 Initializing Correctly....254 Migrations and H2....256 Java Runtime Flags....256 GraalVM, Kotlin/JS, and Kotlin Native....257 Chapter 13: Setup, Teardown, and Dependency Injection with Spring Context....259 Why Spring and Dependency Injection?....260 Setting Up Spring Context....261 Adding Your Data Source....262 lateinit in Kotlin....264 Starting Your Web App....265 Extended Usage....266 Chapter 14: Enterprise Authentication Using Spring Security....268 Preparing Your Web App....268 Setting Up Embedded Jetty....268 Initializing the Servlet....271 Adding Ktor to Your Servlet....272 Using Spring Security....274 Setting Up the Servlet Filter....274 Configuring Spring Security....276 Authenticating Users....278 Filtering Requests....280 Accessing the Logged-In User....281 Chapter 15: Choosing the Right Library....283 What’s a Library?....283 Popularity Is Largely Irrelevant....284 Documentation and Stability Are Important....285 Avoid Following the “X Way”....285 Don’t Shy Away from Platform Libraries....286 Boundaries and Layers....287 Chapter 16: An Assortment of Kotlin Tricks....289 Delegation (by lazy)....289 Inline Functions....290 Reified Generics....292 Contracts....293 And So Much More....294 Appendix A: Using Jooby Instead of Ktor....296 Starting a Server....296 Mapping WebResponse....297 Serving Assets....299 Responding to Requests....300 Authenticating with Forms....301 Authenticating with JWTs....304 Appendix B Using Hoplite Instead of Typesafe Config....305 Loading Config Files....305 Handling JVM Target Version Errors....306 Handling Unknown Environment Variables....307 Masking Secrets....307 Appendix C Using Spek Instead of jUnit 5....309 Writing Spek Tests....309 Structuring Spek Tests....311 Skipping Tests....312 Running Individual Tests....312 Index....314