Why Does Java's HttpURLConnection Fail to Follow HTTP to HTTPS Redirects?

HTTP Redirection from HTTP to HTTPS Causes Connection Failure

When attempting to follow a redirect from HTTP to HTTPS using Java's HttpURLConnection, it may unexpectedly fail. This issue arises because HttpURLConnection's followRedirect() method only follows redirects within the same protocol.

In the provided code, a request is made to "http://httpstat.us/301," which returns a 301 Moved Permanently response indicating a redirect to the HTTPS version of the URL. However, the HttpURLConnection does not follow this redirect.

Why does this occur? HTTP and HTTPS are considered separate protocols by the HTTP protocol specification. Even though HTTPS closely mirrors HTTP, it lacks official recognition within the HTTP framework. Consequently, the HttpURLConnection, without additional configuration, is designed to treat HTTPS as a distinct protocol for security reasons.

Following redirects between HTTP and HTTPS without user consent could pose security risks. For example, client authentication might be enabled automatically for HTTP connections, but the user may intend to browse anonymously. If the connection were to automatically follow an HTTPS redirect, the user's identity could be inadvertently revealed to the server.

Therefore, to maintain security, the HttpURLConnection does not follow redirects from HTTP to HTTPS by default. This behavior cannot be disabled, and it is important to be aware of this limitation when working with HTTP redirects in Java programs.

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