Haken Java Backend Engineer - Spring Boot & AWS | Tokyo

Join one of Japan's leading e-commerce technology companies as a Java Backend Engineer, developing high-performance, secure and scalable backend applications that support a large international digital ecosystem.

Based in Tokyo, this contract opportunity focuses on building and maintaining Java and Spring Boot backend services, with particular emphasis on reliable application architecture, RESTful API development and seamless integration across global technology platforms.

You will contribute to mission-critical fintech, payment and incentive systems that support transaction infrastructure and digital services used by hundreds of millions of users internationally.

Working within an international, English-speaking engineering team, you will collaborate with developers and technical stakeholders to design, develop and enhance backend applications using modern software engineering practices.

The role combines hands-on expertise in Java, Spring Boot, Spring Framework, REST APIs, SQL, relational databases and Docker, alongside opportunities to work with cloud-native architectures and microservices.

You will help ensure that backend systems remain secure, maintainable, efficient and scalable, applying established software design patterns, optimising database operations and supporting containerised application deployment.

This opportunity is ideal for a Java Backend Developer, Spring Boot Engineer, Backend Software Engineer or Microservices Developer seeking to build their career in Tokyo within a large-scale global e-commerce and fintech technology environment.

Key Responsibilities

• Design, develop and maintain secure, scalable Java backend applications using Spring Boot and Spring Framework.
• Build and enhance high-performance RESTful APIs that enable reliable integration across global technology platforms.
• Develop backend services supporting e-commerce, fintech, payment and incentive-related systems.
• Write and optimise SQL queries to improve relational database performance, efficiency and data integrity.
• Apply software design patterns and modular architecture principles to create clean, maintainable and scalable application code.
• Containerise backend services using Docker and support deployment within cloud-based and microservices environments.
• Collaborate with cross-functional Agile engineering teams throughout software design, development, testing and delivery.
• Implement appropriate API security and backend development best practices to support reliable enterprise applications.
• Investigate application performance issues and identify opportunities to improve system efficiency, reliability and scalability.
• Contribute to continuous improvement of backend engineering practices, code quality and software delivery processes.

Required Skills and Qualifications

Experience:

• Professional experience in Java backend software development, with strong hands-on expertise in Spring Boot and Spring Framework.
• Proven experience designing, developing and securing RESTful APIs using established industry best practices.
• Practical experience using Docker to containerise backend applications and support deployment workflows.
• Strong knowledge of relational database design and advanced SQL, including query optimisation and data integrity.
• Ability to apply software design patterns to develop clean, modular, maintainable and scalable backend architectures.
• Understanding of backend application security, performance and reliability in enterprise software environments.
• Experience collaborating with other engineers throughout the software development lifecycle.
• Ability to develop and maintain backend services that integrate effectively with other applications and technology platforms.

Soft Skills:

• Strong analytical thinking and problem-solving skills when developing and improving complex backend systems.
• Effective communication and collaboration skills within international, English-speaking engineering teams.
• High attention to detail and a commitment to producing clean, reliable and maintainable code.
• Ability to work collaboratively with developers and other technical stakeholders in an Agile development environment.
• Proactive approach to identifying opportunities for performance optimisation, code improvement and engineering efficiency.
• Adaptability and willingness to learn new technologies within a large-scale, fast-moving e-commerce technology environment.

Language Requirements:

• English: Business level, equivalent to TOEIC 800+, for technical communication and collaboration within an international engineering team.
• Japanese: Not required. The role operates within an English-speaking engineering environment.

Preferred Skills & Qualifications

• Experience designing, developing and deploying cloud-native applications on Amazon Web Services (AWS).
• Knowledge of CI/CD pipelines and automated software build, testing and deployment workflows.
• Familiarity with automated testing frameworks for Java backend applications.
• Understanding of DevOps practices and collaborative software delivery processes.
• Experience working with microservices architectures and cloud-based backend deployments.
• Exposure to large-scale e-commerce, fintech, payment processing or incentive platform systems.

About the Company

Our client is one of Japan's largest e-commerce technology companies, operating an extensive digital ecosystem that serves hundreds of millions of users internationally.

The organisation develops and maintains large-scale technology platforms spanning e-commerce, fintech, payments and incentive services, supporting transactions and digital experiences across its global business.

Its engineering environment focuses on high-performance applications, scalable backend infrastructure and modern software development technologies, providing opportunities to work on systems with significant operational impact.

The Tokyo-based engineering teams operate in a diverse, international and English-speaking environment, allowing software engineers to collaborate effectively without Japanese language requirements.

The company offers flexible working policies, opportunities for continuous professional development and exposure to modern technology stacks, supporting engineers who want to strengthen their technical expertise.

This position provides an opportunity to contribute directly to business-critical backend systems while developing experience in Java software engineering, cloud-native applications and large-scale fintech-related technology.

Why You'll Love Working Here

• Join one of Japan's leading e-commerce technology companies and contribute to globally used digital services.
• Work on mission-critical fintech, payment and incentive systems supporting hundreds of millions of international users.
• Build and maintain Java and Spring Boot backend applications at significant scale.
• Develop expertise in RESTful APIs, Docker, relational databases and microservices architectures.
• Gain exposure to cloud-native technologies and AWS-based engineering environments.
• Work in a diverse, international and English-speaking team in Tokyo.
• No Japanese language skills required, making this an accessible opportunity for internationally experienced engineers.
• Benefit from flexible working policies and a collaborative engineering culture.
• Strengthen your expertise in software architecture, application security, performance optimisation and modern development practices.
• Build your career within a global e-commerce and fintech ecosystem offering meaningful technical challenges and opportunities for professional growth.

Don't Miss Out - Apply Now!