Lead Java Developer/Solution Architect (6-month contract)

Responsibilities

• gravity9 is recruiting Java engineers and architects for a portfolio of engagements across UK central government. These are large-scale, data-intensive modernisation programmes: replacing legacy systems that carry statutory weight, decomposing monoliths that serve millions of users, and building secure data platforms where access control and auditability are first-class architectural concerns rather than late additions.
• We are hiring across two overlapping profiles — Senior Java Developer and Application / Migration Architect — and expect most people to move between programmes as engagements start and complete. Several of these are hands-on architect roles: you will own design decisions and also write production code
• A greenfield metadata catalogue acting as a federated index over data held across independent domains, so that authorised parties can locate and retrieve data the catalogue itself never holds. The work includes designing an attribute-based access control model over attributes such as clearance, nationality, organisational unit and compartment; enforcing those policies inside the database query path rather than filtering results afterwards; application-layer encryption with externally managed keys; hybrid lexical and semantic search with access filtering applied before candidate retrieval rather than after it; and a tamper-evident audit trail that can reconstruct why a given record was returned, redacted or withheld.
• Real-time decision-support data architecture
• Replacing point-to-point integration across a multi-vendor estate with a microservices architecture and a common data layer, so that operational data flows in near real time instead of over days. The work includes target-state architecture and decision records, change-data-capture ingest pipelines from upstream data services, ontology and mapping-layer design across suppliers with competing data models, separation of system, reference and insight data classes including time-series, and deployment topologies spanning cloud-hosted services down to constrained edge hardware.
• Migrating hundreds of millions of records and tens of terabytes of XML out of a legacy relational platform into a sharded document store, in support of a COBOL-to-Java microservices rewrite. The work includes a configuration-driven XML-to-JSON transformation framework backed by a versioned schema registry — twenty years of history, multiple record types and continual schema and semantic drift; CDC and streaming pipelines, or a checkpointed parallel bulk-extract alternative; a field-level mapping validation and reconciliation framework robust enough to stand up to audit; a replay and failure-diagnostics harness with dead-letter routing and idempotent re-runs; and repeated dress rehearsals toward a single cutover window with no dual running.
• Emphasis varies by role and programme, but MongoDB is the common thread. Every one of these engagements involves modelling for it, migrating onto it, or building on top of it, and genuine depth here is what most differentiates candidates.
• Architecture and design
• • Produce high- and low-level designs, security and data architectures, and architecture decision records — and take them through client design authorities and formal governance gates
• • Design integration boundaries in multi-vendor programmes where you own one component and must collaborate across the seams of others

Languages