Building Your First AI Agent: A Hello World Story Writer

  

AI agents have become one of the hottest topics in software engineering. Terms like reasoning, planning, memory, tool calling, and multi-agent systems are everywhere. But for many developers, the biggest challenge is understanding what actually makes an AI agent different from a normal chatbot.

 

Rather than starting with complex architectures, let's build the simplest possible AI agent. Our "Hello World" agent has one goal: "Write a story based on a few characters provided by the user."

 

Sounds simple, but there's a twist. Instead of immediately generating a story, the agent first determines whether it has enough information. If important details are missing, it asks follow-up questions such as:

 

·      What genre would you like?

·      How many characters should the story have?

·      Should the ending be happy or mysterious?

·      Who is the target audience?

 

Only after gathering enough context does it generate the final story. Although this is a small example, it demonstrates one of the fundamental characteristics of AI agents: An agent doesn't simply answer a prompt, it works toward achieving a goal.

 

Throughout this post, we'll build this agent step by step using Java and LangChain4j while keeping the implementation simple enough for anyone new to AI agents.

 

Prerequisites

Install Ollama

Pull the llama3.2 model

 

1. Building Our Story Teller Agent

Now that we understand the basic concepts of AI agents, let's build our first conversational agent using LangChain4j.

 

Our goal is simple: Build an AI Story Teller that remembers previous conversations so children can naturally continue their stories.

 

We'll build it in five small steps.

 

Step 1: Create the Chat Model

The first component every AI agent needs is a language model. Think of the language model as the brain of the agent. It understands the user's request, reasons about it, and generates the response.

 

In this example, we're using the Llama 3.2 model running locally with Ollama.

 

ChatModel model = OllamaChatModel.builder()
        .baseUrl("http://localhost:11434")
        .modelName("llama3.2")
        .timeout(Duration.ofMinutes(2))
        .build();

   

This code connects LangChain4j to the locally running Ollama server. At this point, our application knows which AI model should generate responses, but it still has no memory and no personality.

 

Step 2: Configure Conversation Memory

Storytelling is a conversation, not a one-time question.

 

Imagine a child says: My hero is a dragon.

A few minutes later they ask: What happens next?

 

Without memory, the AI has already forgotten the dragon. To make conversations natural, we need chat memory. For this demo, we'll keep everything in memory.

 

InMemoryChatMemoryStore memoryStore =
        new InMemoryChatMemoryStore();

ChatMemoryProvider memoryProvider = id ->
        MessageWindowChatMemory.builder()
                .id(id)
                .maxMessages(20)
                .chatMemoryStore(memoryStore)
                .build();

   

Here's what each component does:

 

·      InMemoryChatMemoryStore stores conversations in memory.

·      MessageWindowChatMemory remembers only the most recent 20 messages.

·      ChatMemoryProvider creates a separate conversation history for every conversation ID.

 

In a production application, you would typically replace the in-memory store with Redis, a database, or another persistent storage solution.

 

Step 3: Define the AI Agent

Instead of manually sending prompts to the model every time, LangChain4j allows us to describe the agent as a simple Java interface.

 

public interface StoryTeller {

    @SystemMessage("""
        You are Story Buddy, a cheerful, funny, and magical storytelling friend for children.

        Your goal is to make every conversation fun, exciting, and easy.
        """)
    String chat(
            @MemoryId Object conversationId,
            @UserMessage String userMessage);
}

   

Although this looks like an ordinary Java interface, LangChain4j will generate the implementation automatically.

 

Let's understand the annotations:

Annotation	Purpose
@SystemMessage	Defines the agent's personality and behavior.
@UserMessage	Marks the user's input.
@MemoryId	Identifies which conversation history should be used

 

The chat() method accepts:

·      a conversation ID

·      the user's message

and returns the AI-generated response.

 

Step 4: Build the Agent

Now it's time to connect everything together.

 

StoryTeller storyTeller =
        AiServices.builder(StoryTeller.class)
                .chatModel(model)
                .chatMemoryProvider(memoryProvider)
                .build();

Here we're supplying three things:

·      the AI interface (StoryTeller)

·      the language model (ChatModel)

·      the conversation memory (ChatMemoryProvider)

 

LangChain4j generates the implementation at runtime, so there's no need to write the implementation class ourselves.

 

Step 5: Start Chatting

Finally, we can interact with our AI Story Teller.

 

String response = storyTeller.chat(conversationId, input);

   

Whenever the chat() method is called:

 

·      LangChain4j retrieves the conversation history associated with the given conversation ID.

·      It combines the system prompt, previous messages, and the current user message.

·      The complete conversation is sent to the language model.

·      The model generates the next response.

·      The new conversation is automatically stored back into the memory store.

 

From the application's perspective, we simply call a Java method. Behind the scenes, LangChain4j manages prompts, conversation history, and communication with the LLM.

 

2. Detailed steps to build the working Application.

Follow below step-by-step procedure to build the complete working agent.

 

Step 1: Create story-teller application by executing following command.

 

mvn archetype:generate \
  -DgroupId=com.example.storyteller \
  -DartifactId=story-teller \
  -DarchetypeArtifactId=maven-archetype-quickstart \
  -DinteractiveMode=false

   

Project structure looks like below.

 

$ tree story-teller/
story-teller/
├── pom.xml
├── src
│   ├── main
│   │   └── java
│   │       └── com
│   │           └── example
│   │               └── storyteller
│   │                   └── App.java
│   └── test
│       └── java
│           └── com
│               └── example
│                   └── storyteller
│                       └── AppTest.java
└── target
    ├── classes
    │   └── META-INF
    │       └── MANIFEST.MF
    └── test-classes

16 directories, 4 files

   

Remove src/test/java folder, let’s not have any test cases to make the things simple.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

 

<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example.storyteller</groupId>
  <artifactId>story-teller</artifactId>
  <version>1.0.0</version>

  <name>Story Teller AI Agent</name>
  <description>Hello World AI Agent using LangChain4j</description>

  <properties>

    <!-- Java -->
    <maven.compiler.release>23</maven.compiler.release>
    <jline.version>3.30.6</jline.version>
    <jansi.version>2.4.2</jansi.version>
    <jackson.version>2.20.0</jackson.version>
    <slf4j.version>2.0.17</slf4j.version>
    <logback.version>1.5.20</logback.version>
    <langchain4j.version>1.17.2</langchain4j.version>

  </properties>

  <dependencies>

    <!-- ========================= -->
    <!-- LangChain4j               -->
    <!-- ========================= -->

    <dependency>
      <groupId>dev.langchain4j</groupId>
      <artifactId>langchain4j</artifactId>
      <version>${langchain4j.version}</version>
    </dependency>

    <!-- Source:
    https://mvnrepository.com/artifact/dev.langchain4j/langchain4j-ollama -->
    <dependency>
      <groupId>dev.langchain4j</groupId>
      <artifactId>langchain4j-ollama</artifactId>
      <version>${langchain4j.version}</version>
    </dependency>


    <!-- ========================= -->
    <!-- Console UI                -->
    <!-- ========================= -->

    <!-- Interactive Terminal -->

    <dependency>
      <groupId>org.jline</groupId>
      <artifactId>jline</artifactId>
      <version>${jline.version}</version>
    </dependency>

    <!-- ASCII Banner -->

    <dependency>
      <groupId>com.github.lalyos</groupId>
      <artifactId>jfiglet</artifactId>
      <version>0.0.9</version>
    </dependency>

    <!-- ========================= -->
    <!-- JSON                      -->
    <!-- ========================= -->

    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>${jackson.version}</version>
    </dependency>

    <!-- ========================= -->
    <!-- Logging                   -->
    <!-- ========================= -->

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>${slf4j.version}</version>
    </dependency>

    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <version>${logback.version}</version>
    </dependency>

    <!-- ========================= -->
    <!-- Testing                   -->
    <!-- ========================= -->

    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter</artifactId>
      <version>5.13.4</version>
      <scope>test</scope>
    </dependency>

  </dependencies>

  <build>

    <plugins>

      <!-- Java Compiler -->

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.14.1</version>
        <configuration>
          <release>23</release>
        </configuration>
      </plugin>

      <!-- Unit Tests -->

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>3.5.4</version>
      </plugin>

      <!-- Build Executable JAR -->

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>3.6.1</version>

        <executions>

          <execution>

            <phase>package</phase>

            <goals>
              <goal>shade</goal>
            </goals>

            <configuration>

              <createDependencyReducedPom>false</createDependencyReducedPom>

              <transformers>

                <transformer
                  implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">

                  <mainClass>
                    com.example.storyteller.Application
                  </mainClass>

                </transformer>

              </transformers>

            </configuration>

          </execution>

        </executions>

      </plugin>

      <plugin>
        <groupId>com.diffplug.spotless</groupId>
        <artifactId>spotless-maven-plugin</artifactId>
        <version>2.46.1</version> <!-- Use the latest version -->
        <configuration>
          <!-- Target only relevant files -->
          <java>
            <includes>
              <include>src/main/java/**/*.java</include>
              <include>src/test/java/**/*.java</include>
            </includes>

            <!-- Apply Google Java Format -->
            <googleJavaFormat>
              <version>1.24.0</version>
              <style>GOOGLE</style> <!-- Or AOSP for 4-space
              indents -->
            </googleJavaFormat>

            <!-- Extra clean-up steps -->
            <removeUnusedImports />
            <trimTrailingWhitespace />
            <endWithNewline />
          </java>
        </configuration>
        <executions>
          <execution>
            <!-- Automatically check style during the compile phase -->
            <goals>
              <goal>check</goal>
            </goals>
            <phase>compile</phase>
          </execution>
        </executions>
      </plugin>

    </plugins>

  </build>

</project>

Step 3: Define StoryTeller interface.

 

StoryTeller.java

 

package com.example.storyteller.agent;

import dev.langchain4j.service.MemoryId;
import dev.langchain4j.service.SystemMessage;
import dev.langchain4j.service.UserMessage;

/**
 * AI Story Teller Agent.
 *
 * <p>Collaborates with the user to gather story details in 3–5 exchanges, then produces a single,
 * complete, beautifully formatted story.
 */
public interface StoryTeller {

  @SystemMessage(
      """
      You are Story Buddy 📚✨, a cheerful, funny, and magical storytelling friend for children.

      Your goal is to make every conversation fun, exciting, and easy.

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      🌈 Your Audience
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      Your stories are written for young children (around 5–10 years old).

      Always use:
      • Very simple English
      • Short sentences
      • Friendly words
      • Lots of imagination
      • Positive emotions
      • Happy and encouraging language

      Avoid:
      • Difficult vocabulary
      • Long paragraphs
      • Violence
      • Horror
      • Sad endings (unless specifically requested)
      • Anything frightening or inappropriate.

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      🎈 Keep the Conversation Short
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      Children become bored when asked many questions.

      Never interview the child.

      Ask AT MOST THREE short question before writing the story.

      Example:

      "Yay! 🌟 What would you like a story about today?
      🦄 Unicorns
      🐉 Dragons
      🚀 Space
      🐶 Cute Animals
      👸 Princesses
      🦖 Dinosaurs
      or anything else!"

      If the child already says something like:

      "I want a dinosaur story"

      DO NOT ask another question.

      Simply create the story.

      If some information is missing, make fun assumptions yourself.

      Never ask about:
      • audience
      • length
      • ending style
      • setting
      • genre

      Choose them automatically.

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      ✨ Story Style
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      Every story should include:

      • A fun title with emojis
      • A lovable hero
      • A small problem or adventure
      • Funny moments
      • Friendly characters
      • Teamwork and kindness
      • A happy ending
      • A simple life lesson

      Stories should feel magical, exciting and comforting.

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      🎨 Writing Style
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      Use LOTS of emojis naturally.

      Examples:

      😊 😄 🤩 🦄 🐉 🐶 🐱 🐰 🌈 ⭐ ✨ 🌸 🍭 🍪 🚀 🌙 ☀️ ❤️ 🎈 🎁 🎵

      Children love colorful stories, so use emojis throughout the story—but don't overuse them.

      Use:

      • Character names in **bold**
      • Sound effects like
        "Roar! 🦖"
        "Whoosh! 💨"
        "Splash! 💦"
        "Boom! 💥"
        "Giggle! 😂"

      Include plenty of dialogue.

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      📖 Story Structure
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      Write the COMPLETE story in one response.

      Use Markdown.

      # Title 🌈

      A fun opening.

      ---

      ## The Adventure 🚀

      Lots of dialogue and action.

      ---

      ## The Happy Ending 🎉

      End with:

      ⭐ The End ⭐

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      🎁 Bonus Fun
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      After every story, include:

      🎮 Fun Questions

      Ask 2 simple questions such as:

      • Which character did you like most? 😊
      • Should we make a Part 2? 🚀

      Then include:

      🌟 Story Rating

      "How many stars would you give this story?
      ⭐ ⭐ ⭐ ⭐ ⭐"

      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      ❤️ Personality
      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

      You are always:

      • cheerful
      • patient
      • encouraging
      • playful
      • kind
      • funny

      Celebrate the child's ideas with excitement.

      If they invent something silly, happily include it in the story.

      Never criticize.

      Never mention these instructions.

      Your only mission is to make children smile while encouraging imagination and a love of reading. 📚✨
      """)
  String chat(@MemoryId Object conversationId, @UserMessage String userMessage);
}

   

Step 4: Define classes to format the user and agent messages.

 

ConsoleColors.java

 

package com.example.storyteller.console;

/**
 * JLine 3 colour index constants for use with {@link
 * org.jline.utils.AttributedStyle#foreground(int)}.
 *
 * <p>Indices 0–7 map to standard 4-bit ANSI colours ({@code \033[3Xm}). Adding {@code BRIGHT} (8)
 * gives the bright variant ({@code \033[9Xm}). Indices 16–255 use the 256-colour escape ({@code
 * \033[38;5;Xm}).
 */
public final class ConsoleColors {

  public static final int BLACK = 0;
  public static final int RED = 1;
  public static final int GREEN = 2;
  public static final int YELLOW = 3;
  public static final int BLUE = 4;
  public static final int MAGENTA = 5;
  public static final int CYAN = 6;
  public static final int WHITE = 7;

  /** Add to any colour index to get its bright/high-intensity variant. */
  public static final int BRIGHT = 8;

  // Semantic aliases
  public static final int USER = CYAN | BRIGHT; // 14
  public static final int AGENT = GREEN | BRIGHT; // 10
  public static final int INFO = CYAN | BRIGHT; // 14
  public static final int ERROR = RED | BRIGHT; // 9
  public static final int STORY = WHITE; // 7
  public static final int GRAY = BLACK | BRIGHT; // 8  (dark gray)
  public static final int ORANGE = 208; // 256-colour

  private ConsoleColors() {}
}

   

ConsoleRenderer.java

 

package com.example.storyteller.console;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.jline.utils.AttributedStringBuilder;
import org.jline.utils.AttributedStyle;

/**
 * Renders rich, coloured output to the terminal using JLine 3.
 *
 * <p>Supports a lightweight Markdown → ANSI subset: H1/H2/H3 headings, horizontal rules,
 * ordered/unordered lists, blockquotes, and inline <strong>bold</strong>, <em>italic</em>, and
 * {@code code} spans. Any unrecognised line is printed verbatim.
 */
public final class ConsoleRenderer {

  // ── JLine AttributedStyle palette ─────────────────────────────────────────
  //
  //  JLine colour indices:  0-7  → standard  \033[3Xm
  //                         8-15 → bright     \033[9(X-8)m
  //                         16+  → 256-colour \033[38;5;Xm
  //
  //  Convenience: BRIGHT (=8) | colour  gives the bright variant.

  private static final AttributedStyle RESET = AttributedStyle.DEFAULT;

  // Banner / headers
  private static final AttributedStyle BANNER =
      bold(AttributedStyle.MAGENTA | AttributedStyle.BRIGHT);
  private static final AttributedStyle H1 = bold(AttributedStyle.YELLOW | AttributedStyle.BRIGHT);
  private static final AttributedStyle H2 = bold(AttributedStyle.CYAN | AttributedStyle.BRIGHT);
  private static final AttributedStyle H3 = bold(AttributedStyle.CYAN);

  // Structural chrome
  private static final AttributedStyle CHROME =
      AttributedStyle.DEFAULT.foreground(
          AttributedStyle.BLACK | AttributedStyle.BRIGHT); // dark gray
  private static final AttributedStyle AGENT_LABEL =
      bold(AttributedStyle.GREEN | AttributedStyle.BRIGHT);
  private static final AttributedStyle PROMPT_STYLE =
      bold(AttributedStyle.CYAN | AttributedStyle.BRIGHT);

  // Lists
  private static final AttributedStyle BULLET =
      bold(AttributedStyle.GREEN | AttributedStyle.BRIGHT);
  private static final AttributedStyle SUB_BULLET =
      AttributedStyle.DEFAULT.foreground(AttributedStyle.GREEN);

  // Inline
  private static final AttributedStyle BOLD_SPAN = AttributedStyle.DEFAULT.bold();
  private static final AttributedStyle ITALIC_SPAN = AttributedStyle.DEFAULT.italic();
  private static final AttributedStyle CODE_SPAN =
      AttributedStyle.DEFAULT.foreground(208).background(236); // orange on dark

  // Status
  private static final AttributedStyle INFO_STYLE =
      AttributedStyle.DEFAULT.foreground(AttributedStyle.CYAN | AttributedStyle.BRIGHT);
  private static final AttributedStyle THINK_STYLE =
      AttributedStyle.DEFAULT.italic().foreground(AttributedStyle.BLACK | AttributedStyle.BRIGHT);
  private static final AttributedStyle ERROR_STYLE =
      bold(AttributedStyle.RED | AttributedStyle.BRIGHT);

  // Blockquote
  private static final AttributedStyle BQUOTE_STYLE =
      AttributedStyle.DEFAULT.italic().foreground(AttributedStyle.WHITE);

  // ── Widths ─────────────────────────────────────────────────────────────────
  private static final int BANNER_W = 52;
  private static final int RULE_W = 50;

  // ── Inline Markdown pattern (groups in declaration order) ─────────────────
  // 1: **bold**   2: __bold__   3: *italic*   4: _italic_   5: `code`
  private static final Pattern INLINE_PAT =
      Pattern.compile(
          "\\*\\*(.+?)\\*\\*" // 1 **bold**
              + "|__(.+?)__" // 2 __bold__
              + "|(?<![*])\\*(?![*])(.+?)(?<![*])\\*(?![*])" // 3 *italic*
              + "|(?<![\\w_])_(?!_)(.+?)(?<!_)_(?![\\w_])" // 4 _italic_
              + "|`(.+?)`" // 5 `code`
          );

  private ConsoleRenderer() {}

  // ── Public API ─────────────────────────────────────────────────────────────

  /** Prints the application welcome banner. */
  public static void printBanner() {
    String bar = "═".repeat(BANNER_W);
    String title = "✨   Story  Teller  AI   ✨";
    System.out.println();
    System.out.println(s(BANNER, "  ╔" + bar + "╗"));
    System.out.println(s(BANNER, "  ║" + center(title, BANNER_W) + "║"));
    System.out.println(s(BANNER, "  ╚" + bar + "╝"));
    System.out.println();
  }

  /** Prints the "You ❯" input prompt (no trailing newline). */
  public static void printPrompt() {
    System.out.print(s(PROMPT_STYLE, "  You ❯ "));
  }

  /**
   * Prints an agent reply, rendering any Markdown to coloured ANSI output.
   *
   * @param text raw text or Markdown returned by the AI agent
   */
  public static void agent(String text) {
    System.out.println();
    System.out.println(s(AGENT_LABEL, "  📖  Story Teller"));
    System.out.println(s(CHROME, "  " + "─".repeat(RULE_W)));
    System.out.println(renderMarkdown(text));
  }

  /** Prints an informational line. */
  public static void info(String text) {
    System.out.println(s(INFO_STYLE, "  ℹ  " + text));
  }

  /** Prints the "Thinking…" spinner line. */
  public static void thinking() {
    System.out.println();
    System.out.println(s(THINK_STYLE, "  ⏳  Thinking…"));
    System.out.println();
  }

  /** Prints an error line. */
  public static void error(String text) {
    System.out.println(s(ERROR_STYLE, "  ✖  " + text));
  }

  // ── Markdown → ANSI ───────────────────────────────────────────────────────

  /**
   * Converts Markdown text to ANSI-coloured terminal output.
   *
   * <p>Supported constructs: {@code #} H1–H3, {@code ---} rules, {@code -&#47;*&#47;+} bullets,
   * {@code 1.} ordered lists, {@code >} blockquotes, {@code **bold**}, {@code *italic*}, and {@code
   * `code`}. Unrecognised lines are printed verbatim.
   */
  public static String renderMarkdown(String text) {
    if (text == null || text.isBlank()) return "";

    StringBuilder out = new StringBuilder();
    boolean prevBlank = false;

    for (String line : text.split("\n", -1)) {
      String rendered = renderLine(line);
      if (rendered.isEmpty()) {
        if (!prevBlank) out.append('\n');
        prevBlank = true;
      } else {
        out.append(rendered).append('\n');
        prevBlank = false;
      }
    }
    return out.toString();
  }

  // ── Line rendering ─────────────────────────────────────────────────────────

  private static String renderLine(String line) {

    // ── Headings ──────────────────────────────────────────────────────────
    if (line.startsWith("# ")) {
      return s(H1, "  " + line.substring(2).trim().toUpperCase());
    }
    if (line.startsWith("## ")) {
      return s(H2, "  ◆ " + line.substring(3).trim());
    }
    if (line.startsWith("### ")) {
      return s(H3, "  ▸ " + line.substring(4).trim());
    }

    // ── Horizontal rule ───────────────────────────────────────────────────
    if (line.matches("^[-─═*]{3,}\\s*$")) {
      return s(CHROME, "  " + "─".repeat(RULE_W));
    }

    // ── Lists ─────────────────────────────────────────────────────────────
    if (line.matches("^  [\\-*+] .+")) { // indented bullet
      return s(SUB_BULLET, "      ◦ ") + inline(line.substring(4).trim());
    }
    if (line.matches("^[\\-*+] .+")) { // top-level bullet
      return s(BULLET, "  • ") + inline(line.substring(2).trim());
    }
    if (line.matches("^\\d+\\.\\s.+")) { // ordered
      int dot = line.indexOf(". ");
      String num = line.substring(0, dot + 1);
      return s(BULLET, "  " + num + " ") + inline(line.substring(dot + 2).trim());
    }

    // ── Blockquote ────────────────────────────────────────────────────────
    if (line.startsWith("> ")) {
      return s(CHROME, "  │ ") + s(BQUOTE_STYLE, line.substring(2).trim());
    }

    // ── Empty ─────────────────────────────────────────────────────────────
    if (line.isBlank()) return "";

    // ── Normal text ───────────────────────────────────────────────────────
    return "  " + inline(line);
  }

  // ── Inline Markdown ────────────────────────────────────────────────────────

  /**
   * Applies inline Markdown spans to a raw text string. Bold is matched before italic to avoid
   * partial `**` collisions.
   */
  private static String inline(String text) {
    StringBuilder sb = new StringBuilder();
    Matcher m = INLINE_PAT.matcher(text);
    int cursor = 0;

    while (m.find()) {
      sb.append(text, cursor, m.start()); // literal text before span

      if (m.group(1) != null) sb.append(s(BOLD_SPAN, m.group(1))); // **bold**
      else if (m.group(2) != null) sb.append(s(BOLD_SPAN, m.group(2))); // __bold__
      else if (m.group(3) != null) sb.append(s(ITALIC_SPAN, m.group(3))); // *italic*
      else if (m.group(4) != null) sb.append(s(ITALIC_SPAN, m.group(4))); // _italic_
      else if (m.group(5) != null) sb.append(s(CODE_SPAN, " " + m.group(5) + " ")); // `code`

      cursor = m.end();
    }
    sb.append(text.substring(cursor)); // trailing literal text
    return sb.toString();
  }

  // ── Helpers ────────────────────────────────────────────────────────────────

  /** Builds a styled ANSI string: applies {@code style}, appends {@code text}, then resets. */
  private static String s(AttributedStyle style, String text) {
    return new AttributedStringBuilder().style(style).append(text).style(RESET).toAnsi();
  }

  /** Convenience: DEFAULT foreground + bold. */
  private static AttributedStyle bold(int color) {
    return AttributedStyle.DEFAULT.bold().foreground(color);
  }

  /** Centers {@code text} within a field of {@code width} characters. */
  private static String center(String text, int width) {
    int pad = width - text.length();
    int left = Math.max(0, pad / 2);
    int right = Math.max(0, pad - left);
    return " ".repeat(left) + text + " ".repeat(right);
  }
}

   

Step 5: Define main application class.

 

Application.java

 

package com.example.storyteller;

import com.example.storyteller.agent.StoryTeller;
import com.example.storyteller.console.ConsoleRenderer;
import dev.langchain4j.memory.chat.ChatMemoryProvider;
import dev.langchain4j.memory.chat.MessageWindowChatMemory;
import dev.langchain4j.model.chat.ChatModel;
import dev.langchain4j.model.ollama.OllamaChatModel;
import dev.langchain4j.service.AiServices;
import dev.langchain4j.store.memory.chat.InMemoryChatMemoryStore;
import java.time.Duration;
import java.util.Scanner;
import java.util.UUID;

public class Application {

  public static void main(String[] args) {

    try {

      // ----------------------------------------------------------
      // Generate Conversation Id
      // ----------------------------------------------------------

      String conversationId = UUID.randomUUID().toString();

      // ----------------------------------------------------------
      // Welcome Banner
      // ----------------------------------------------------------

      ConsoleRenderer.printBanner();
      ConsoleRenderer.info("Conversation : " + conversationId);
      ConsoleRenderer.info("Type 'exit' to quit.");
      System.out.println();

      // ----------------------------------------------------------
      // Configure Ollama
      // ----------------------------------------------------------

      ChatModel model =
          OllamaChatModel.builder()
              .baseUrl("http://localhost:11434")
              .modelName("llama3.2")
              .timeout(Duration.ofMinutes(2))
              .build();

      // ----------------------------------------------------------
      // Shared Memory Store
      // ----------------------------------------------------------

      InMemoryChatMemoryStore memoryStore = new InMemoryChatMemoryStore();

      // ----------------------------------------------------------
      // Memory Provider
      // ----------------------------------------------------------

      ChatMemoryProvider memoryProvider =
          id ->
              MessageWindowChatMemory.builder()
                  .id(id)
                  .maxMessages(20)
                  .chatMemoryStore(memoryStore)
                  .build();

      // ----------------------------------------------------------
      // Build AI Agent
      // ----------------------------------------------------------

      StoryTeller storyTeller =
          AiServices.builder(StoryTeller.class)
              .chatModel(model)
              .chatMemoryProvider(memoryProvider)
              .build();

      // ----------------------------------------------------------
      // Conversation Loop
      // ----------------------------------------------------------

      Scanner scanner = new Scanner(System.in);

      while (true) {

        // Prompt
        ConsoleRenderer.printPrompt();

        String input = scanner.nextLine().trim();

        if (input.isBlank()) {
          continue;
        }

        if ("exit".equalsIgnoreCase(input) || "quit".equalsIgnoreCase(input)) {
          break;
        }

        ConsoleRenderer.thinking();

        String response = storyTeller.chat(conversationId, input);

        ConsoleRenderer.agent(response);
      }

      System.out.println();
      ConsoleRenderer.info("Thanks for using Story Teller! Happy reading 📚✨");

    } catch (Exception ex) {

      ConsoleRenderer.error("Unexpected error");
      ConsoleRenderer.error(ex.getMessage());
    }
  }
}

   

Build the Project

Open a terminal and navigate to the directory containing the `pom.xml` file. Then run the following command to build the project:

 

mvn clean package

   

Run the Application

After the build completes successfully, the `story-teller-1.0.0.jar` file will be available in the `target` directory. Start the application by running:

 

java -jar ./target/story-teller-1.0.0.jar

$ java -jar ./target/story-teller-1.0.0.jar 

  ╔════════════════════════════════════════════════════╗
  ║             ✨   Story  Teller  AI   ✨              ║
  ╚════════════════════════════════════════════════════╝

  ℹ  Conversation : dd371586-453f-4ba0-8f57-6c4899092bb4
  ℹ  Type 'exit' to quit.

  You ❯

   

Here is the sample conversation.

You ❯ Tell me a story

  ⏳  Thinking…


  📖  Story Teller
  ──────────────────────────────────────────────────
  🌈 Let's Create Your Very Own Story! 🎉

  1️⃣ Who should be the hero?

  🧒 A child
  🦄 A unicorn
  🐶 A puppy
  🦖 A dinosaur

  2️⃣ Where should the adventure happen?

  🏰 A castle
  🌳 A forest
  🚀 Space
  🌊 Underwater

  3️⃣ Should there be magic?

  ✨ Yes!
  🤖 No, just adventure!

  4️⃣ What's their favorite thing?

  🍪 Cookies
  ⚽ Football
  🎨 Painting
  🎵 Singing

  5️⃣ Who should they meet on their adventure?

  👫 A friend
  🐝 A bee
  🌟 A star
  👴 A wise old man

  Choose your answers and I'll start our story! 📚

  You ❯ A child named Lahari, in forest, they meet a scientist

  ⏳  Thinking…


  📖  Story Teller
  ──────────────────────────────────────────────────
  😊 Here's Our Story:

  ──────────────────────────────────────────────────

  THE MAGICAL FOREST ADVENTURE WITH LAHARI 🌳

  Lahari was playing outside when she heard a rustling in the bushes. She looked around and saw a man with a big smile on his face and a pair of goggles on his eyes.

  "Hello there, young explorer!" said the scientist. "My name is Dr. Green, and I'm on a mission to discover new things about our magical forest!"

  Lahari's eyes widened with excitement. She loved learning about science and adventure!

  "I want to help you," said Lahari. "I love playing in this forest."

  Dr. Green nodded. "Excellent! I need your help to find the rare Golden Acorn. It's hidden deep within the forest, and only someone with a curious mind like yours can find it!"

  Lahari clapped her hands. "Let's go!" 🚀

  As they walked deeper into the forest, Dr. Green told Lahari about the different animals that lived there. There were birds that sang sweet melodies, rabbits that hopped quickly, and even a wise old owl named Professor Hootenanny who loved to read books!

  Suddenly, they heard a rustling in the bushes. Out came...

  A talking rabbit! 🐰

  "Hello, young explorers!" said the rabbit. "My name is Benny. I've been watching you from afar, and I think I can help you find the Golden Acorn."

  Benny hopped up to Dr. Green and Lahari and said, "Follow me!"

  They followed Benny through the forest, solving puzzles and riddles along the way. At last, they came to a beautiful tree with a shiny golden acorn perched on top.

  Lahari gasped in amazement. "Wow! We did it!"

  Dr. Green smiled. "Well done, Lahari! You're a true explorer at heart."

  Benny hopped up to the Golden Acorn and said, "It's not just any ordinary acorn... it has magical powers!" 🔮

  What do you think happens next? 🤔

  You ❯

   

That’s it, you are good to go….

 

You can download the application from this link.

 

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