Freelance Java Backend Developer Jobs in Belleville, IL

If you've spent the last few years building your expertise in backend engineering, Java or Python development, and missiondriven systems, and you're ready for work that actually moves the needle, this is the kind of opportunity cleared engineers pursue when they want real impact. If you take pride in your craft, write your own resume, and deliver results that senior leaders actually see, you'll thrive here.

We're hiring a Backend Software Engineer to support a highvisibility application relied on across the organization for data analysis, reporting, and operational decisionmaking. You'll design and build scalable backend services, develop RESTful APIs, integrate complex data sources, and ensure system reliability and performance in a Linuxbased environment.

Our primary development team operates out of Gaithersburg, MD, but we also support onsite engineers in Alexandria, VA; Chantilly, VA; Aurora, CO; St. Louis, MO; and Tucson, AZ, giving top talent multiple paths to join the mission.

And while the requisition requirements may seem standard fair, the position is not; as it will join a high performing team that is changing the way digital engineering and mission operations intelligence is enabled for our customer.

Why This Role Stands Out

• High Impact: Your services power a widely used application that drives realtime decisions

• High Visibility: Collaborate directly with engineering teams and mission stakeholders

• Career Growth: Deepen your expertise in backend architecture, API design, and scalable systems

• Challenging Work: Build and optimize complex backend features

Key Responsibilities

• Backend Development:Design, develop, test, and maintain backend services using Java or Python

• REST API Development:Design and implement RESTful services to support application functionality and integrations

• Object-Oriented Design:Apply strong object-oriented design principles to build scalable and maintainable systems

• Database Development:Write and optimize SQL queries to support application functionality and performance

• Data Source Integration Coordination: Coordinate with external teams to understand data sources, interfaces, and access patterns, and translate requirements into backend integrations

• System Design Contribution:Participate in technical design discussions and contribute to backend architecture decisions

• Linux Environments:Develop, deploy, and troubleshoot applications within Linux-based environments

• System Troubleshooting:Diagnose and resolve issues across application and database layers

• Code Quality & Best Practices:Participate in code reviews and ensure adherence to engineering standards

Basic Qualifications

• Bachelor's degree in Computer Science, Software Engineering, or a related field with 8-12 years of experience; or a Master's degree with 6-10 years of experience

• U.S. Citizenship

• Active TS/SCI clearance with the ability to successfully pass a Polygraph

• Strong professional experience developing backend applications in Java or Python

• Proven ability to design and develop RESTful APIs that support scalable application functionality

• Solid SQL experience, including writing and optimizing queries across relational databases

• Confident working in Linuxbased environments

• Ability to work independently and drive solutions to moderately complex and complex technical challenges

Preferred Qualifications

• Experience withApache Airflow or similar workflow orchestration technologies

• Experience with geospatial data and querying (e.g., PostGIS)

• Experience withSpring Boot, Django, or similar backend frameworks

• Experience withCI/CD pipelines (GitLab, Jenkins, etc.)

• Familiarity withcontainerization (Docker, OpenShift, Kubernetes)

• Exposure tocloud environments (AWS or Azure)

• Experience working inAgile development environments

#MARU

If you're looking for comfort, keep scrolling. At Leidos, we outthink, outbuild, and outpace the status quo - because the mission demands it. We're not hiring followers. We're recruiting the ones who disrupt, provoke, and refuse to fail. Step 10 is ancient history. We're already at step 30 - and moving faster than anyone else dares.

The Leidos pay range for this job level is a general guideline onlyand not a guarantee of compensation or salary. Additional factors considered in extending an offer include (but are not limited to) responsibilities of the job, education, experience, knowledge, skills, and abilities, as well as internal equity, alignment with market data, applicable bargaining agreement (if any), or other law.