Senior Software Engineer (Java)

optimum solutions (singapore) pte ltd; Singapore; On-site; SGD 108,000 - 180,000; Full time

Job summary

Optimum Solutions Singapore Pte Ltd is seeking an experienced Backend Java Developer with strong core Java and API design expertise to design, build, and maintain RESTful services.

You will work with Spring Boot, tackle multi-database persistence, asynchronous processing, and ensure robust, scalable backend architecture. The role emphasizes clean code, testing (JUnit), code reviews, and solid OO and functional programming practices across the stack.

Qualifications

• 5+ years of hands-on Java 11/17+ development with strong core API skills.
• Deep knowledge of Spring Boot, Spring Core, Spring MVC and DI.
• Solid RESTful design, HTTP status codes, JSON processing and error handling.
• Advanced PostgreSQL/MySQL/Oracle with Hibernate and Spring Data JPA.
• Experience with Kafka or RabbitMQ for messaging/event streaming.
• Proficiency with design patterns, TDD/unit testing (JUnit 5, Mockito) and build tools (Maven/Gradle).

Responsibilities

• Design, build, and maintain RESTful APIs and backend services using Java 11+ and Spring Boot.
• Implement SOLID, object‑oriented design and reusable modules.
• Author OpenAPI/Swagger documentation for endpoints and contracts.
• Leverage concurrency utilities and asynchronous patterns for performance.
• Diagnose memory leaks and GC bottlenecks using profiling tools.
• Design and optimize relational and NoSQL database schemas.

Skills

Java 11/17+

Spring Boot

RESTful APIs

Concurrency

Streams API

SOLID Design

Tools

PostgreSQL

MySQL

Oracle

Hibernate

Redis

Swagger/OpenAPI

Maven

Gradle

Flyway/Liquibase

Job description

Position Overview

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, optimizing 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).