获取“java.net.ProtocolException：服务器重定向次数太多”错误

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.

Answer 4

I had faced the same problem and it took considerable amount of time to understand the problem. So to summarize the problem was in mismatch of headers.

Consider below being my Resource

  @GET
  @Path("booksMasterData")
  @Produces(Array(core.MediaType.APPLICATION_JSON))
  def booksMasterData(@QueryParam("stockStatus") stockStatus : String): Response = {
 // some logic here to get the books and send it back
    }

And here is client code, which was trying to connect to my above resource

ClientResponse clientResponse = restClient.resource("http://localhost:8080/booksService").path("rest").path("catalogue").path("booksMasterData").accept("application/boks-master-data+json").get(ClientResponse.class);

And the error was coming on exactly above line.

What was the problem?

My Resource was using

"application/json"

in

@Produces annotation

and my client was using

accept("application/boks-master-data+json") and this was the problem.

It took me long to find out this as the error was no where related. Break through was when I tried to access my resource in postman with

Accept-> "application/json" header

it worked fine, however with

Accept-> "application/boks-master-data+json" header it doesnt.

And again, even Postman was not giving me proper error. The error was too generic. Please see the below image for reference.