Java Backend Engineer (IM Server)

Responsibilities1. Design & implement IM server.2. Develop video/audio conferencing modules.3. Build file management.4. Implement calendar & scheduling: events, invitations, conflict detection, reminders, external integration.5. Solve high-concurrency, low-latency, high-availability challenges.6. Design distributed components: message routing, push, offline messages, data consistency.7. Collaborate with product/client/infra teams on APIs & data models.8. Performance tuning, capacity planning, fault-tolerance for core services.9. Troubleshoot production issues, root cause analysis, monitoring & alerting.10. Code reviews, documentation, knowledge sharing. Requirements1. Bachelor's degree or above in Computer Science or related fields; 3+ years Java backend.2. Strong Java, concurrency, networking, JVM tuning.3. Familiar with WebSocket/MQTT/SIP/WebRTC signaling is a plus.4. File storage, access control, or calendar logic experience preferred.5. Solid system design; high-traffic, low-latency experience.6. Strong problem-solving, online debugging, performance optimization.7. Good communication, ownership, responsibility.