How to Correctly Set the User-Agent in Java URLConnection?

Setting User Agent of a Java URLConnection

When attempting to parse a webpage using Java with URLConnection and setting the user-agent to a specified value, an additional "Java/1.5.0_19" may be appended to the end. This arises due to a limitation in older versions of Java.

Solution (Java 1.6.30 and Newer)

In Java 1.6.30 and newer, this issue has been resolved. Setting the user agent using setRequestProperty("User-Agent", "Mozilla ...") now works correctly without appending the Java version.

Verification

To verify this, you can listen on a port using netcat, which displays the raw HTTP headers of incoming requests. Without setting the user agent, the headers will show:

GET /foobar HTTP/1.1
User-Agent: Java/1.6.0_30
Host: localhost:8080
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-alive

When setting the user agent, the headers will instead show:

GET /foobar HTTP/1.1
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4; en-US; rv:1.9.2.2) Gecko/20100316 Firefox/3.6.2
Host: localhost:8080
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-alive

Example Code (Java 1.6.30 )

The following code example demonstrates how to correctly set the user agent:

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;


public class TestUrlOpener {

    public static void main(String[] args) throws IOException {
        URL url = new URL("http://localhost:8080/foobar");
        URLConnection hc = url.openConnection();
        hc.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4; en-US; rv:1.9.2.2) Gecko/20100316 Firefox/3.6.2");

        System.out.println(hc.getContentType());
    }

}

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