How to Ensure HttpURLConnection Utilizes a Proxy and Handles Authentication?

Establishing Proxy Connectivity for HttpURLConnection

When attempting to determine whether an HttpURLConnection is using a proxy, the following code may falsely return false:

conn = new URL(urlString).openConnection();
System.out.println("Proxy? " + conn.usingProxy());

This behavior occurs despite being connected through a proxy server. The Java Virtual Machine (JVM) typically retrieves proxy information from the operating system settings. However, it's possible for the JVM to be unaware of the proxy configuration in certain circumstances.

Proxies and JVM Proxy Settings

To ensure that HttpURLConnection utilizes the appropriate proxy, it is necessary to explicitly provide the proxy information. This can be achieved by constructing a Proxy instance and passing it to the openConnection(proxy) method:

//Proxy instance, proxy ip = 10.0.0.1 with port 8080
Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("10.0.0.1", 8080));
conn = new URL(urlString).openConnection(proxy);

Authenticating Proxy Connections

If the proxy requires authentication, the HttpURLConnection will respond with a 407 response code. To resolve this issue, an Authenticator can be configured as follows:

Authenticator authenticator = new Authenticator() {

    public PasswordAuthentication getPasswordAuthentication() {
        return (new PasswordAuthentication("user",
                "password".toCharArray()));
    }
};
Authenticator.setDefault(authenticator);

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