OutputFormatter

An OutputFormatter is a software component that translates in-memory data into a serialized representation for output, such as an HTTP response, a file, or a console stream. By isolating the rendering logic from business logic, formatters enable the same data to be presented in multiple formats depending on context and consumer needs.

Formatters commonly support several media types, including text/plain, application/json, application/xml, text/html, and text/csv. In web frameworks, formatters are selected through content negotiation, where the client requests a preferred format and the framework chooses an appropriate formatter that can serialize the response type.

Formatters usually implement a common interface or base class that provides methods to check compatibility with a given type and to write the serialized output to a writer or stream. They may support streaming to handle large outputs, or buffer the entire payload. They also handle encoding and locale-specific formatting, such as number and date formats.

Typical usage includes rendering API responses, generating reports, or writing logs in structured formats. They are often plug-ins or services that can be registered or discovered by the hosting framework.

Design considerations include performance, error handling, security (proper escaping and avoidance of data leakage), and extensibility. Adding a new format typically requires implementing the formatter interface and registering it with the framework.

Examples of formats provided by common ecosystems include JSON, XML, HTML, plain text, and CSV. OutputFormatters play a key role in how software systems adapt data presentation to different clients and contexts.