Small wireless nodes in sensor networks are increasing being deployed in a wide variety of applications. In this paper, we present ActiveBeans, a generic and secure software platform in a small wireless node employing the Java technologies for data management and sensor/actuator control applications inside a building. Small wireless nodes have been deployed everywhere, and have been used to manage data for applications, perform operations using the data or control sensor/actuator attached to the node. To deal with management data items and controlled devices in a node in a uniform manner, we introduce a node description in the XML format. ActiveBeans provides a Java software platform to access the node description securely. ActiveBeans has the following features: a small Java virtual machine with small footprint management for various input and output device using the generic framework, the data management, and the fine-grained access control. To decrease the Java program size, a generator customizes and optimizes the access control module in a host machine, which is downloaded into the node with a lightweight wireless management protocol.