Object life cycles and thread safety

There are five kinds of objects in the Java API Client with different life cycles:

Object mapper: Stateless and thread-safe, but can be costly to create. It’s usually a singleton that is created at application startup and used to create the transport.
Transport: Thread-safe, holds network resources through the underlying HTTP client. A transport object is associated with an Elasticsearch cluster and has to be explicitly closed to release the underlying resources such as network connections.
Clients: Immutable, stateless and thread-safe. These are very lightweight objects that just wrap a transport and provide API endpoints as methods. Closing a client closes the underlying transport.
Builders: Mutable, non thread-safe. Builders are transient objects that should not be reused after calling build().
Requests & other API objects: Immutable, thread-safe. If your application uses the same request or same parts of a request over and over, these objects can be prepared in advance and reused across multiple calls over multiple clients with different transports.