Exposing MCP from Legacy Java: Architecture Patterns That Actually Scale

Large Language Models are no longer just consumers of public APIs. With the Model Context Protocol (MCP) , they become first-class clients of enterprise systems. This creates a new architectural challenge for the enterprise: How do we expose MCP servers from legacy Jakarta EE applications without breaking the systems we rely on today? This isn't about greenfield projects. This is about WildFly, Payara, WebLogic, SOAP endpoints, EJBs, and shared databases. The key insight: MCP is not “just another API.” It changes traffic patterns, trust boundaries, and scaling behavior. Treating it like standard REST leads to failure modes you already know too well. MCP Changes the Shape of Integration Traditional integrations assume human-driven request rates and predictable shapes. MCP breaks these assumptions. An AI client can: Invoke many tools in rapid succession. Call internal operations humans never touch. Generate load patterns that look like accidental DDoS. Pattern 1: The MCP Gateway The safe