HTML builder example pattern in Kotlin - Mini Project: Build & Apply

Build a Simple HTML Page Using Kotlin HTML Builder

📖 Scenario: You want to create a simple HTML page using Kotlin's HTML builder pattern. This helps you write HTML code in Kotlin in a clear and structured way.

🎯 Goal: Build a small HTML page with a header, a paragraph, and a list using Kotlin's HTML builder pattern.

📋 What You'll Learn

Create an HTML document with a head and body

Add a title inside the head

Add a h1 header inside the body

Add a p paragraph inside the body

Add an unordered list ul with three list items li

💡 Why This Matters

🌍 Real World

Kotlin HTML builder is used to generate HTML content programmatically, useful in web servers, templates, or static site generation.

💼 Career

Understanding Kotlin DSLs and HTML generation is valuable for backend developers working with Kotlin frameworks like Ktor or building web tools.

1

Create the HTML builder setup

Create a variable called htmlContent and assign it the result of kotlinx.html.stream.createHTML().html with an empty lambda block {}.

Kotlin

# Create a variable called htmlContent using createHTML().html {}
# Your code here

Hint

Use val htmlContent = createHTML().html { } to start building your HTML.

2

Add the head section with a title

Inside the html builder block, add a head block. Inside head, add a title with the text "My Kotlin Page".

Kotlin

import kotlinx.html.stream.createHTML

val htmlContent = createHTML().html {
    // Add head with title here
}

Hint

Use head { title { +"My Kotlin Page" } } inside the html block.

3

Add body with header and paragraph

Inside the html builder block, after head, add a body block. Inside body, add a h1 header with text "Welcome to Kotlin HTML Builder" and a p paragraph with text "This page is built using Kotlin.".

Kotlin

import kotlinx.html.stream.createHTML

val htmlContent = createHTML().html {
    head {
        title { +"My Kotlin Page" }
    }
    // Add body with h1 and p here
}

Hint

Use body { h1 { ... } p { ... } } inside the html block after head.

4

Add an unordered list and print the HTML

Inside the body block, add an unordered list ul with three list items li containing the texts "Item 1", "Item 2", and "Item 3". Then, print the htmlContent variable.

Kotlin

import kotlinx.html.stream.createHTML

val htmlContent = createHTML().html {
    head {
        title { +"My Kotlin Page" }
    }
    body {
        h1 { +"Welcome to Kotlin HTML Builder" }
        p { +"This page is built using Kotlin." }
        // Add ul with li items here
    }
}

// Print the htmlContent
# Your code here

Hint

Use ul { li { ... } } inside body and then println(htmlContent) to show the HTML.

Practice

1. What is the main purpose of the HTML builder pattern in Kotlin?

easy

A. To write HTML code clearly and safely using Kotlin syntax

B. To convert HTML files into Kotlin source code automatically

C. To create CSS stylesheets within Kotlin code

D. To execute HTML code as Kotlin functions

Solution

1. Step 1: Understand the pattern's goal

   The HTML builder pattern is designed to help write HTML code inside Kotlin programs clearly and safely.

2. Step 2: Compare options with the pattern's purpose

   Only To write HTML code clearly and safely using Kotlin syntax correctly states that it helps write HTML code clearly and safely using Kotlin syntax.

3. Final Answer:

   To write HTML code clearly and safely using Kotlin syntax -> Option A

4. Quick Check:

   HTML builder pattern = clear, safe HTML in Kotlin [OK]

Hint: Focus on clarity and safety in HTML code generation [OK]

Common Mistakes:

• Confusing HTML builder with HTML parsing
• Thinking it generates CSS styles
• Assuming it runs HTML as Kotlin code

2. Which Kotlin syntax correctly starts an HTML builder block for a div element?

easy

A. html.div { }

B. html { div { } }

C. html.div() { }

D. html.div[] { }

Solution

1. Step 1: Recall Kotlin DSL syntax for HTML builder

   The HTML builder uses nested lambdas like html { div { } } to create tags.

2. Step 2: Check each option's syntax correctness

   html { div { } } uses the correct lambda block syntax. Options B, C, and D use invalid Kotlin syntax for this pattern.

3. Final Answer:

   html { div { } } -> Option B

4. Quick Check:

   Correct lambda block syntax = html { div { } } [OK]

Hint: Remember: use curly braces {} for nested tags in Kotlin DSL [OK]

Common Mistakes:

• Using dot notation without lambda braces
• Adding parentheses incorrectly
• Using square brackets instead of braces

3. What is the output of this Kotlin HTML builder code?

val result = html {
  body {
    p { +"Hello" }
    p { +"World" }
  }
}
println(result)

medium

A. HelloWorld

B. HelloWorld

C. HelloWorld

D. HelloWorld

Solution

1. Step 1: Understand the structure built by the code

   The code creates an html tag containing a body tag, which contains two p tags with text "Hello" and "World".

2. Step 2: Match the output string with the structure

   <html><body><p>Hello</p><p>World</p></body></html> correctly shows the full HTML with nested tags. Other options miss tags or combine paragraphs incorrectly.

3. Final Answer:

   <html><body><p>Hello</p><p>World</p></body></html> -> Option A

4. Quick Check:

   Nested tags output = full html with body and paragraphs [OK]

Hint: Remember each tag creates nested HTML elements [OK]

Common Mistakes:

• Forgetting the outer <html> tag
• Combining text inside one <p> tag
• Omitting the <body> tag

4. Identify the error in this Kotlin HTML builder code:

html {
  body {
    p { +"Welcome" }
    div
      p { +"Nested" }
  }
}

medium

A. body tag cannot contain div tag

B. Incorrect use of + operator inside p tag

C. html block must be assigned to a variable

D. Missing braces {} after div tag

Solution

1. Step 1: Check syntax for nested tags

   In Kotlin HTML builder, tags like div must be followed by braces to define their content.

2. Step 2: Identify the missing braces

   The div tag is written without braces, so the nested p tag is not properly inside it.

3. Final Answer:

   Missing braces {} after div tag -> Option D

4. Quick Check:

   Every tag needs braces for children [OK]

Hint: Always add {} after tags to nest children [OK]

Common Mistakes:

• Omitting braces for nested tags
• Misusing + operator for text
• Thinking body can't contain div

5. How would you modify this Kotlin HTML builder code to add a class attribute to the div tag?

html {
  body {
    div {
      p { +"Content" }
    }
  }
}

hard

A. div("class" to "container") { p { +"Content" } }

B. div(class = "container") { p { +"Content" } }

C. div { attributes["class"] = "container"; p { +"Content" } }

D. div { setAttribute("class", "container"); p { +"Content" } }

Solution

1. Step 1: Recall how to set attributes in Kotlin HTML builder

   Attributes are set inside the tag block using attributes["name"] = "value".

2. Step 2: Check each option for correct attribute setting

   div { attributes["class"] = "container"; p { +"Content" } } uses attributes["class"] = "container" inside the div block, which is the correct way. Options A, C, and D use invalid syntax or a method not available in this pattern.

3. Final Answer:

   div { attributes["class"] = "container"; p { +"Content" } } -> Option C

4. Quick Check:

   Set attributes inside block with attributes["name"] = value [OK]

Hint: Use attributes map inside tag block to set HTML attributes [OK]

Common Mistakes:

• Trying to pass attributes as function parameters
• Using non-existent setAttribute method
• Setting attributes outside tag block