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

Nov 24, 2024 am 02:59 AM

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:

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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

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

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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

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Example Code (Java 1.6.30 )

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

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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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