update: update the Spring Boot tutorial

docs/topics/jvm/jvm-create-project-with-spring-boot.md

@@ -12,6 +12,10 @@ The first part of the tutorial shows you how to create a Spring Boot project in
 
 Download and install the latest version of [IntelliJ IDEA Ultimate Edition](https://www.jetbrains.com/idea/download/index.html).
 
+> If you use IntelliJ IDEA Community Edition or another IDE, you can generate a Spring Boot project using a [web-based project generator](https://start.spring.io).
+> 
+{type="note"}
+
 ## Create a Spring Boot project
 
 Create a new Spring Boot project with Kotlin by using the Project Wizard in IntelliJ IDEA Ultimate Edition:
@@ -49,7 +53,9 @@ Create a new Spring Boot project with Kotlin by using the Project Wizard in Inte
 
 6. Click **Create** to generate and set up the project.
 
-   The IDE will generate and open the new project. It may take some time to download and import the project dependencies.
+   > The IDE will generate and open a new project. It may take some time to download and import the project dependencies.
+   >
+   {type="tip"} 
 
 7. After this, you can observe the following structure in the **Project view**:
 
@@ -71,15 +77,18 @@ Here is the full script with the explanation of all parts and dependencies:
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile // For `KotlinCompile` task below
 
 plugins { 
-    id("org.springframework.boot") version "2.7.1"
-    id("io.spring.dependency-management") version "1.0.11.RELEASE"
+    id("org.springframework.boot") version "3.1.2"
+    id("io.spring.dependency-management") version "1.1.2"
     kotlin("jvm") version "%kotlinVersion%" // The version of Kotlin to use
     kotlin("plugin.spring") version "%kotlinVersion%" // The Kotlin Spring plugin
 }
 
 group = "com.example"
-version = "0.0.1-SNAPSHOT" 
-java.sourceCompatibility = JavaVersion.VERSION_17 
+version = "0.0.1-SNAPSHOT"
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+}
 
 repositories {
     mavenCentral()
@@ -126,7 +135,7 @@ As you can see, there are a few Kotlin-related artifacts added to the Gradle bui
 Open the `DemoApplication.kt` file:
 
 ```kotlin
-package demo
+package com.example.demo
 
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication
@@ -224,7 +233,7 @@ class MessageController {
 Here is a complete code of the `DemoApplication.kt`:
 
 ```kotlin
-package demo
+package com.example.demo
 
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication

docs/topics/jvm/jvm-spring-boot-add-data-class.md

@@ -98,7 +98,7 @@ The response from `MessageController` will now be a JSON document containing a c
 Here is a complete code of the `DemoApplication.kt`:
 
 ```kotlin
-package demo
+package com.example.demo
 
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication

docs/topics/jvm/jvm-spring-boot-add-db-support.md

@@ -36,7 +36,7 @@ class MessageService(val db: JdbcTemplate) {
 
 <deflist collapsible="true">
    <def title="Constructor argument and dependency injection – (val db: JdbcTemplate)">
-      <p>A class in Kotlin can have a primary constructor and one or more <a href="classes.md#secondary-constructors">secondary constructors</a>.
+      <p>A class in Kotlin has a primary constructor. It can also have one or more <a href="classes.md#secondary-constructors">secondary constructors</a>.
       The <i>primary constructor</i> is a part of the class header, and it goes after the class name and optional type parameters. In our case, the constructor is <code>(val db: JdbcTemplate)</code>.</p>
       <p><code>val db: JdbcTemplate</code> is the constructor's argument:</p>
       <code style="block" lang="kotlin">
@@ -171,7 +171,7 @@ Configure the database in the application:
 You should use an HTTP client to work with previously created endpoints. In IntelliJ IDEA, use the embedded HTTP client:
 
 1. Run the application. Once the application is up and running, you can execute POST requests to store messages in the database.
-   Create the `requests.http` file and add the following HTTP requests:
+   Create the `requests.http` file in the `src/main/resources` folder and add the following HTTP requests:
 
    ```http request
    ### Post "Hello!"
@@ -256,13 +256,15 @@ Extend the functionality of the application to retrieve the individual messages
     }
     ```
 
-    > The `query()` function that is used to fetch the message by its id is a [Kotlin extension function](extensions.md#extension-functions) provided by the Spring Framework and requires an additional import as in the code above.
+    > The `.query()` function that is used to fetch the message by its id is a [Kotlin extension function](extensions.md#extension-functions) provided by the Spring Framework and requires an additional import as in the code above.
     >
     {type="note"}
 
 2. Add the new `index(...)` function with the `id` parameter to the `MessageController` class:
 
     ```kotlin
+    import org.springframework.web.bind.annotation.*
+
     @RestController
     class MessageController(val service: MessageService) {
         @GetMapping("/")
@@ -294,6 +296,64 @@ Extend the functionality of the application to retrieve the individual messages
     </def>
     </deflist>
 
+Here is a complete code of the `DemoApplication.kt`:
+
+```kotlin
+package com.example.demo
+
+import org.springframework.boot.autoconfigure.SpringBootApplication
+import org.springframework.boot.runApplication
+import org.springframework.stereotype.Service
+import org.springframework.jdbc.core.JdbcTemplate
+import java.util.UUID
+import org.springframework.jdbc.core.query
+import org.springframework.web.bind.annotation.*
+
+
+@SpringBootApplication
+class DemoApplication
+
+fun main(args: Array<String>) {
+    runApplication<DemoApplication>(*args)
+}
+
+@RestController
+class MessageController(val service: MessageService) {
+    @GetMapping("/")
+    fun index(): List<Message> = service.findMessages()
+
+    @GetMapping("/{id}")
+    fun index(@PathVariable id: String): List<Message> =
+        service.findMessageById(id)
+
+    @PostMapping("/")
+    fun post(@RequestBody message: Message) {
+        service.save(message)
+    }
+}
+
+data class Message(val id: String?, val text: String)
+
+@Service
+class MessageService(val db: JdbcTemplate) {
+
+    fun findMessages(): List<Message> = db.query("select * from messages") { response, _ ->
+        Message(response.getString("id"), response.getString("text"))
+    }
+
+    fun findMessageById(id: String): List<Message> = db.query("select * from messages where id = ?", id) { response, _ ->
+        Message(response.getString("id"), response.getString("text"))
+    }
+
+    fun save(message: Message) {
+        val id = message.id ?: UUID.randomUUID().toString()
+        db.update("insert into messages values ( ?, ? )",
+            id, message.text)
+    }
+}
+```
+{initial-collapse-state="collapsed"}
+
 ## Run the application
 
 The Spring application is ready to run:

docs/topics/jvm/jvm-spring-boot-using-crudrepository.md

@@ -42,6 +42,8 @@ First, you need to adjust the `Message` class for work with the `CrudRepository`
 3. Update the `MessageService` class. It will now call to the `MessageRepository` instead of executing SQL queries:
 
     ```kotlin
+    import java.util.*
+
     @Service
     class MessageService(val db: MessageRepository) {
         fun findMessages(): List<Message> = db.findAll().toList()
@@ -60,7 +62,7 @@ First, you need to adjust the `Message` class for work with the `CrudRepository`
     <deflist collapsible="true">
        <def title="Extension functions">
           <p>The return type of the <code>findById()</code> function in the <code>CrudRepository</code> interface is an instance of the <code>Optional</code> class. However, it would be convenient to return a <code>List</code> with a single message for consistency. For that, you need to unwrap the <code>Optional</code> value if it’s present, and return a list with the value. This can be implemented as an <a href="extensions.md#extension-functions">extension function</a> to the <code>Optional</code> type.</p>
-          <p>In the code, <code>Optional&lt;out T&gt;.toList()</code>, <code>toList()</code> is the extension function for <code>Optional</code>. Extension functions allow you to write additional functions to any classes, which is especially useful when you want to extend functionality of some library class.</p>
+          <p>In the code, <code>Optional&lt;out T&gt;.toList()</code>, <code>.toList()</code> is the extension function for <code>Optional</code>. Extension functions allow you to write additional functions to any classes, which is especially useful when you want to extend functionality of some library class.</p>
        </def>
        <def title="CrudRepository save() function">
           <p><a href="https://docs.spring.io/spring-data/jdbc/docs/current/reference/html/#jdbc.entity-persistence">This function works</a> with an assumption that the new object doesn’t have an id in the database. Hence, the id <b>should be null</b> for insertion.</p>
@@ -72,12 +74,81 @@ First, you need to adjust the `Message` class for work with the `CrudRepository`
 4. Update the messages table definition to generate the ids for the inserted objects. Since `id` is a string, you can use the `RANDOM_UUID()` function to generate the id value by default:
 
     ```sql
-    CREATE TABLE messages (
-       id                     VARCHAR(60)  DEFAULT RANDOM_UUID() PRIMARY KEY,
-       text                   VARCHAR      NOT NULL
-       );
+    CREATE TABLE IF NOT EXISTS messages (
+        id      VARCHAR(60)  DEFAULT RANDOM_UUID() PRIMARY KEY,
+        text    VARCHAR      NOT NULL
+    );
     ```
 
+5. Update the name of the database in the `application.properties` file located in the `src/main/resources` folder:
+
+   ```none
+   spring.datasource.driver-class-name=org.h2.Driver
+   spring.datasource.url=jdbc:h2:file:./data/testdb2
+   spring.datasource.username=name
+   spring.datasource.password=password
+   spring.sql.init.schema-locations=classpath:schema.sql
+   spring.sql.init.mode=always
+   ```
+
+Here is the complete code for `DemoApplication.kt`:
+
+```kotlin
+package com.example.demo
+
+import org.springframework.boot.autoconfigure.SpringBootApplication
+import org.springframework.boot.runApplication
+import org.springframework.data.annotation.Id
+import org.springframework.data.relational.core.mapping.Table
+import org.springframework.data.repository.CrudRepository
+import org.springframework.stereotype.Service
+import org.springframework.web.bind.annotation.*
+import java.util.*
+
+
+@SpringBootApplication
+class DemoApplication
+
+fun main(args: Array<String>) {
+    runApplication<DemoApplication>(*args)
+}
+
+@RestController
+class MessageController(val service: MessageService) {
+    @GetMapping("/")
+    fun index(): List<Message> = service.findMessages()
+
+    @GetMapping("/{id}")
+    fun index(@PathVariable id: String): List<Message> =
+        service.findMessageById(id)
+
+    @PostMapping("/")
+    fun post(@RequestBody message: Message) {
+        service.save(message)
+    }
+}
+
+interface MessageRepository : CrudRepository<Message, String>
+
+@Table("MESSAGES")
+data class Message(@Id var id: String?, val text: String)
+
+@Service
+class MessageService(val db: MessageRepository) {
+    fun findMessages(): List<Message> = db.findAll().toList()
+
+    fun findMessageById(id: String): List<Message> = db.findById(id).toList()
+
+    fun save(message: Message) {
+        db.save(message)
+    }
+
+    fun <T : Any> Optional<out T>.toList(): List<T> =
+        if (isPresent) listOf(get()) else emptyList()
+}
+```
+{initial-collapse-state="collapsed"}
+
 ## Run the application
 
 The application is ready to run again.