Senior Backend Java Developer (API & Software Engineering)

Optimum Solutions Pte Ltd; Singapore; On-site; SGD 90,000 - 130,000; Full time

Job summary

Optimum Solutions Pte Ltd is seeking an experienced Backend Java Developer to design, build, and maintain high-throughput, secure RESTful APIs and enterprise backend components. You will focus on scalable code, multi-database interactions, and strong OOP and functional practices across the stack.

The role emphasizes Java 11+/17+, Spring Boot, REST API design, and robust database work with relational and NoSQL systems, plus security and observability considerations.

Qualifications

• 5+ years of hands-on Java development with Java 11/17+ and strong core Java knowledge.
• Experience with Spring Boot, Spring Core, Spring MVC and DI.
• Proficient in designing RESTful APIs, database design, and asynchronous programming.

Responsibilities

• Design, build, and maintain RESTful APIs and backend services using Java (11+) and the Spring Boot framework.
• Implement clean architectural patterns, object-oriented design principles (SOLID), and reusable modules.
• Author OpenAPI/Swagger docs for REST endpoints and internal contracts.

Skills

Java

Spring Boot

REST APIs

Concurrency

SQL/Databases

Spring Data JPA/Hibernate

OpenAPI/Swagger

OAuth2/JWT Security

JUnit/Mockito

Logging/Monitoring

Tools

Kafka/RabbitMQ

Flyway/Liquibase

Docker

Redis

Maven/Gradle

Job description

We are seeking an experienced Backend Java Developer with strong core Java capabilities and a deep focus on API design and backend architecture. In this role, you will design, build, and maintain high-throughput, secure RESTful APIs and enterprise backend components. You will focus on writing scalable code, optimising multi-database interactions, mastering asynchronous execution, and driving sound object-oriented and functional programming practices across the stack.

Key Responsibilities

• Design, build, and maintain RESTful APIs and backend services using Java (11+) and the Spring / Spring Boot framework.
• Implement clean architectural patterns, object-oriented design principles (SOLID), and reusable software modules.
• Author standard OpenAPI/Swagger documentation for REST endpoints and internal contracts.
• Leverage Java concurrency utilities, multithreading frameworks, and asynchronous programming patterns to ensure efficient application performance.
• Diagnose, debug, and resolve memory leaks, thread contention, and garbage collection bottleneck issues using Java profiling tools.
• Design and optimize relational (PostgreSQL, MySQL, Oracle) and NoSQL database schemas.
• Manage data persistence and transactional boundaries using Spring Data JPA / Hibernate.
• Write tuned SQL queries, establish effective database indexing, and configure connection pooling and caching strategies (e.g., Redis).
• Implement standard API security mechanisms (OAuth2, JWT authentication, authorization, and data sanitization).
• Build structured logging, health checks, and application metrics using standard logging frameworks (Logback, SLF4J).
• Write clean, maintainable, modular, and unit-tested code using JUnit and Mockito.
• Participate in code reviews, technical architecture reviews, and maintain test coverage across applications.

Required Technical Qualifications

• 5+ years of hands-on software development experience using Java 11/17+ with deep knowledge of Collections, Streams API, Multithreading/Concurrency, Memory Model, and Exception Handling.
• Strong expertise in Spring Boot, Spring Core, Spring MVC, and dependency injection paradigms.
• Deep understanding of RESTful architectural styles, HTTP status codes, JSON payload processing, custom middleware, and error-handling patterns.
• Advanced proficiency in Spring Data JPA / Hibernate, multi-datasource routing, raw SQL query tuning, and database migration tooling (Flyway/Liquibase).
• Practical experience with message brokers and event streaming architectures using Kafka or RabbitMQ.
• Solid grasp of Design Patterns (Factory, Builder, Singleton, Strategy), TDD/unit testing principles (JUnit 5, Mockito), and build tools (Maven / Gradle).

Preferred Qualifications

• Understanding of containerization basics (Docker) and modern CI/CD deployment workflows.
• Familiarity with microservice resiliency concepts (Rate Limiting, Circuit Breakers, Retry policies).
• Experience with caching layers and distributed system synchronization.