403,401规格严格

java.io.IOException: Server returned HTTP response code: 403 for URL

但是自己却可以用浏览器访问，发现可能是服务器对我们这种java程序屏蔽了。

因为服务器的安全设置不接受Java程序作为客户端访问，解决方案是设置客户端的User Agent

url = new URL("url");
            HttpURLConnection connection = (HttpURLConnection) url.
                openConnection();
            connection.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");

这样就可以访问了。

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java.io.IOException: Server returned HTTP response code: 401 for URL

// Install the custom authenticator
Authenticator.setDefault(new MyAuthenticator());

// Access the page
try {
    // Create a URL for the desired page
    URL url = new URL("http://hostname/index.html");

    // Read all the text returned by the server
    BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
    String str;
    while ((str = in.readLine()) != null) {
        // str is one line of text; readLine() strips the newline character(s)
    }
    in.close();
} catch (MalformedURLException e) {
} catch (IOException e) {
}

public class MyAuthenticator extends Authenticator {
    // This method is called when a password-protected URL is accessed
    protected PasswordAuthentication getPasswordAuthentication() {
        // Get information about the request
        String promptString = getRequestingPrompt();
        String hostname = getRequestingHost();
        InetAddress ipaddr = getRequestingSite();
        int port = getRequestingPort();

        // Get the username from the user...
        String username = "myusername";

        // Get the password from the user...
        String password = "mypassword";

        // Return the information
        return new PasswordAuthentication(username, password.toCharArray());
    }
}