Getting "java.net.ProtocolException: Server redirected too many times" Error

Question

I'm making a simple URL request with code like this:

URL url = new URL(webpage);
URLConnection urlConnection = url.openConnection();
InputStream is = urlConnection.getInputStream();

But on that last line, I'm getting the "redirected too many times error". If my "webpage" var is, say, google.com then it works fine, but when I try to use my servlet's URL then it fails. It seems I can adjust the number of times it follows the redirects (default is 20) with this:

System.setProperty("http.maxRedirects", "100");

But when I crank it up to, say, 100 it definitely takes longer to throw the error so I know it is trying. However, the URL to my servlet works fine in (any) browser and using the "persist" option in firebug it seems to only be redirecting once.

A bit more info on my servlet ... it is running in tomcat and fronted by apache using 'mod-proxy-ajp'. Also of note, it is using form authentication so any URL you enter should redirect you to the login page. As I said, this works correctly in all browsers, but for some reason the redirect isn't working with the URLConnection in Java 6.

Thanks for reading ... ideas?

Answer 1

It's apparently redirecting in an infinite loop because you don't maintain the user session. The session is usually backed by a cookie. You need to create a CookieManager before you use URLConnection.

// First set the default cookie manager.
CookieHandler.setDefault(new CookieManager(null, CookiePolicy.ACCEPT_ALL));

// All the following subsequent URLConnections will use the same cookie manager.
URLConnection connection = new URL(url).openConnection();
// ...

connection = new URL(url).openConnection();
// ...

connection = new URL(url).openConnection();
// ...

See also:

• Using java.net.URLConnection to fire and handle HTTP requests

Answer 2

Duse, I have add this lines:

java.net.CookieManager cm = new java.net.CookieManager();
java.net.CookieHandler.setDefault(cm);

See this example:

java.net.CookieManager cm = new java.net.CookieManager();
java.net.CookieHandler.setDefault(cm);
String buf="";
dk = new DAKABrowser(input.getText());
try {
    URL url = new URL(dk.toURL(input.getText()));
    DataInputStream dis = new DataInputStream(url.openStream());
    String inputLine;
    while ((inputLine = dis.readLine()) != null) {
        buf+=inputLine;
        output.append(inputLine+"\n");
    }
    dis.close();
} 
catch (MalformedURLException me) {
    System.out.println("MalformedURLException: " + me);
}
catch (IOException ioe) {
    System.out.println("IOException: " + ioe);
}
titulo.setText(dk.getTitle(buf));

Answer 3

I was using Jenkins on Tomcat6 on a unix environment and got this bug. For some reason, upgrading to Java7 solved it. I'd be interested to know exactly why that fixed it.