URLConnection

URLConnection is an abstraction that represents a communications link to a resource identified by a URL. In the Java standard library, it is an abstract class in the java.net package that encapsulates the ability to open a connection to a resource and to read from or write to it. Instances are created by calling URL.openConnection(), which returns a URLConnection object (often a concrete subclass such as HttpURLConnection for HTTP resources).

A URLConnection manages details such as request headers and properties, input and output streams, and connection timeouts. It supports configuring behavior via methods such as setRequestProperty, getRequestProperty, setDoInput, setDoOutput, setConnectTimeout, and setReadTimeout. The connect() method establishes the connection, though streams retrieval often implicitly triggers a connection.

For HTTP, HttpURLConnection adds HTTP-specific capabilities, including methods to set the request method (GET, POST, etc.), access the response code and message, and inspect response headers. Other protocols provide different subclasses with protocol-specific behavior.

Usage typically involves creating a URL, opening a connection, configuring preferences, obtaining an InputStream to read data or an OutputStream to write, and then closing the streams. The disconnect() method can be used to release network resources, and streams should be closed in a finally block or via a resource-management construct.

Limitations and notes include that URLConnection provides a general interface, so not all protocols support every feature. Caching behavior and authentication may depend on the protocol and environment. Modern Java code may alternatively use newer HTTP APIs, but URLConnection remains a foundational, backward-compatible mechanism for accessing resources via URLs.