Agentic AI in Practice — From Concept to Code

A demo project showcasing AI agent orchestration using Spring Boot, LangChain4j, and LangGraph4j. Features two banking-domain agents that demonstrate the ReAct (Reason + Act) pattern with real-time visualization.

Agents

1. Payment Investigation Agent

Investigates failed payment transactions by autonomously querying multiple banking systems.

How it works:

• Accepts a transaction ID
• Queries the transaction database
• Routes to the correct payment network (VISA / GIRO / PayNow) based on the provider
• Looks up error codes
• Produces a structured investigation report with root cause and recommendations

Tools: queryTransactionDb, checkCardNetwork, checkGiroStatus, checkPayNowStatus, lookupErrorCodes

2. Credit Risk Assessment Agent

Evaluates loan applicants by gathering data from multiple sources and producing a risk assessment.

How it works:

• Accepts an applicant ID
• Fetches credit bureau data
• Verifies income
• Checks existing loans
• Applies risk rules
• Flags anomalies
• Produces a risk assessment report with approval/denial recommendation

Tools: fetchCreditBureau, verifyIncome, checkExistingLoans, applyRiskRules, flagAnomalies

Architecture

Both agents use the ReAct pattern — a single agent that loops through:

Think -> Pick Tool -> Execute -> Observe -> Repeat (until done)

Built with LangGraph4j's StateGraph:

START -> Human Input -> Agent (ReAct) <-> Tool Executor -> Final Report -> END

Note: ReAct was chosen for demo purposes — it visually shows the LLM reasoning at each step. In production, the Credit Risk agent would benefit from a fixed parallel graph for better performance and lower cost.

Tech Stack

Component	Version
Java	21
Spring Boot	3.4.1
LangChain4j	1.1.0
LangGraph4j	1.8.4
LLM	OpenAI GPT-4o-mini

Getting Started

Prerequisites

• Java 21+
• An OpenAI API key

Setup

1. Clone the repository:

   git clone https://github.com/rkp4u/agent_demo.git
   cd agent_demo

2. Set your API key (choose one):

   Option A — Environment variable:

   export OPENAI_API_KEY=your-key-here

   Option B — .env file (not committed):

   echo "export OPENAI_API_KEY=your-key-here" > .env
   source .env

   Option C — IntelliJ: Add OPENAI_API_KEY=your-key-here in Run Configuration > Environment variables.

3. Run the application:

   ./gradlew bootRun

4. Open the UI: http://localhost:8080

API Endpoints

Method	Endpoint	Description
POST	/api/payment/investigate	Run payment investigation
POST	/api/creditrisk/assess	Run credit risk assessment

Payment Investigation:

curl -X POST http://localhost:8080/api/payment/investigate \
  -H "Content-Type: application/json" \
  -d '{"transactionId": "TXN-98432"}'

Credit Risk Assessment:

curl -X POST http://localhost:8080/api/creditrisk/assess \
  -H "Content-Type: application/json" \
  -d '{"applicantId": "APP-2024-1001"}'

UI

The demo includes a hybrid visualization UI combining:

• Agent Graph (left panel) — shows the LangGraph nodes lighting up as execution progresses
• Chat Interface (right panel) — displays the agent's reasoning chain with expandable steps and a final report card

Project Structure

src/main/java/com/demo/agent/
  AgentDemoApplication.java
  payment/
    PaymentAgentGraph.java          # LangGraph state machine
    PaymentAgentState.java          # Agent state definition
    PaymentAgentService.java        # Service layer
    PaymentAgentController.java     # REST endpoint
    tools/
      QueryTransactionDb.java       # Simulated transaction DB
      CheckCardNetwork.java         # VISA/Mastercard lookup
      CheckGiroStatus.java          # GIRO transfer status
      CheckPayNowStatus.java        # PayNow transfer status
      LookupErrorCodes.java         # Error code reference
      PaymentToolExecutor.java      # Tool dispatcher
  creditrisk/
    CreditRiskAgentGraph.java
    CreditRiskAgentState.java
    CreditRiskAgentService.java
    CreditRiskAgentController.java
    tools/
      FetchCreditBureau.java
      VerifyIncome.java
      CheckExistingLoans.java
      ApplyRiskRules.java
      FlagAnomalies.java
      CreditRiskToolExecutor.java
src/main/resources/
  application.yml                   # Config (API key via env var)
  static/
    index.html                      # Demo UI