A Java JMS (Java Message Service) developer designs, builds, and maintains applications using the Java JMS API, enabling two components to send and receive messages asynchronously. They work on creating distributed applications that are loosely coupled, reliable, and asynchronous. Their tasks include writing code for message-driven beans, configuring JMS server settings, handling messaging patterns, and ensuring message reliability and asynchronous communication. They also troubleshoot and fix any issues in the messaging system. Knowledge of JMS providers, such as ActiveMQ or RabbitMQ, and understanding of concepts like point-to-point, publish-subscribe models, and message queues are key for this role.