How Can I Set a Custom User Agent for Java URLConnections?

Customizing the User Agent for Java URLConnections

When establishing a connection to a webpage using Java's URLConnection, you may wish to set a custom user agent. This is commonly used to mimic the behavior of a particular web browser or to identify your application. However, attempts to set a non-default user agent often result in the default value being appended.

Solution:

In earlier versions of Java, setting a custom user agent via setRequestProperty("User-Agent", "custom_agent") appended "Java/xx" to the end. This issue has been resolved in Java 1.6.30 and newer.

Example:

import java.net.URL;
import java.net.URLConnection;

public class CustomUserAgent {

    public static void main(String[] args) throws Exception {
        URL url = new URL("http://example.com");
        URLConnection connection = url.openConnection();
        connection.setRequestProperty("User-Agent", "Mozilla/5.0");
        System.out.println(connection.getRequestProperty("User-Agent"));
    }
}

In Java 1.6.30 or later, this code will output "Mozilla/5.0" without the appended "Java/xx".

Netcat Verification:

To verify that the custom user agent is being used, you can listen on a port using netcat:

$ nc -l -p 8080

When the above code is executed, you should see the custom user agent in the HTTP headers received by netcat.

Alternative Solutions:

If you are still facing issues with appending "Java/xx" in older Java versions, you can try using a third-party HTTP library that allows you to fully control the User-Agent header.

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