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Midas Core - Setup Fixes Documentation

Problem Summary

The Spring Boot application was failing to start during tests with IllegalStateException: Failed to load ApplicationContext. All test classes (TaskOneTests through TaskFiveTests) were failing.

Root Cause

The main application.yml configuration file in the project root was empty, causing Spring Boot to fail during context initialization. The application needed:

  1. Kafka topic configuration
  2. Kafka serialization settings for JSON objects
  3. Database configuration
  4. JPA/Hibernate settings

Solution Applied

Created application.yml with Complete Configuration

general:
  kafka-topic: trader-updates

spring:
  kafka:
    bootstrap-servers: localhost:9092
    producer:
      key-serializer: org.apache.kafka.common.serialization.StringSerializer
      value-serializer: org.springframework.kafka.support.serializer.JsonSerializer
    consumer:
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value-deserializer: org.springframework.kafka.support.serializer.JsonDeserializer
      properties:
        spring.json.trusted.packages: "*"

  datasource:
    url: jdbc:h2:mem:testdb
    driver-class-name: org.h2.Driver
    username: sa
    password:

  jpa:
    hibernate:
      ddl-auto: create-drop
    show-sql: false

Configuration Breakdown

1. General Configuration

  • kafka-topic: Set to trader-updates as required by Task 1 instructions

2. Kafka Configuration

  • bootstrap-servers: Points to localhost:9092 for local Kafka broker
  • Producer Settings:
    • key-serializer: StringSerializer for message keys
    • value-serializer: JsonSerializer to serialize Transaction objects as JSON
  • Consumer Settings:
    • key-deserializer: StringDeserializer for message keys
    • value-deserializer: JsonDeserializer to deserialize JSON back to Transaction objects
    • spring.json.trusted.packages: Set to "*" to allow deserialization of all packages

3. Database Configuration (H2)

  • url: In-memory H2 database named testdb
  • driver-class-name: H2 JDBC driver
  • username: sa (default H2 admin user)
  • password: Empty (no password required for test database)

4. JPA/Hibernate Configuration

  • ddl-auto: create-drop - Creates schema on startup, drops on shutdown (ideal for testing)
  • show-sql: false - Disables SQL logging to keep test output clean

Why JSON Serialization Was Needed

The KafkaProducer class uses KafkaTemplate<String, Transaction>, which means it sends Transaction objects (not strings) to Kafka. The Transaction class is a POJO with:

  • senderId (long)
  • recipientId (long)
  • amount (float)

Without JSON serialization configured, Kafka tried to use StringSerializer for Transaction objects, causing SerializationException.

Test Results

Before Fix

[ERROR] Failed to load ApplicationContext
[ERROR] Tests run: 5, Failures: 0, Errors: 5, Skipped: 0

After Fix

[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

Task 1 Output

---begin output ---
1142725631254665682354316777216387420489
---end output ---

Files Modified

  1. application.yml - Created with complete Spring Boot configuration

Dependencies Already Present

The pom.xml already had all required dependencies:

  • spring-boot-starter-web (3.2.5)
  • spring-boot-starter-data-jpa (3.2.5)
  • spring-kafka (3.1.4)
  • h2 database (2.2.224)
  • spring-boot-starter-test (3.2.5)
  • spring-kafka-test (3.1.4)
  • testcontainers-kafka (1.19.1)

Next Steps

With the configuration fixed, you can now:

  1. Submit the Task 1 output: 1142725631254665682354316777216387420489
  2. Proceed with implementing the remaining tasks (Task 2-5)
  3. Run all tests with: mvn test
  4. Run specific test with: mvn -Dtest=TaskOneTests test

Key Takeaway

Always ensure your application.yml or application.properties file contains the necessary configuration for Spring Boot to initialize the ApplicationContext, especially when working with:

  • Kafka messaging
  • Database connections
  • Custom properties referenced in @Value annotations