Why would a "java.net.ConnectException: Connection timed out" exception occur when URL is up?

Sarah_Haskins_16677 0
Viewed 505417

I'm getting a ConnectException: Connection timed out with some frequency from my code. The URL I am trying to hit is up. The same code works for some users, but not others. It seems like once one user starts to get this exception they continue to get the exception.

Here is the stack trace:

java.net.ConnectException: Connection timed out
Caused by: java.net.ConnectException: Connection timed out
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
    at java.net.Socket.connect(Socket.java:516)
    at java.net.Socket.connect(Socket.java:466)
    at sun.net.NetworkClient.doConnect(NetworkClient.java:157)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:365)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:477)
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:214)
    at sun.net.www.http.HttpClient.New(HttpClient.java:287)
    at sun.net.www.http.HttpClient.New(HttpClient.java:299)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:796)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:748)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:673)
    at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:840)

Here is a snippet from my code:

URLConnection urlConnection = null;
OutputStream outputStream = null;
OutputStreamWriter outputStreamWriter = null;
InputStream inputStream = null;

try {
    URL url = new URL(urlBase);
    urlConnection = url.openConnection();
    urlConnection.setDoOutput(true);

    outputStream = urlConnection.getOutputStream(); // exception occurs on this line
    outputStreamWriter = new OutputStreamWriter(outputStream);
    outputStreamWriter.write(urlString);
    outputStreamWriter.flush();
    inputStream = urlConnection.getInputStream();
    String response = IOUtils.toString(inputStream);
    return processResponse(urlString, urlBase, response);
} catch (IOException e) {
    throw new Exception("Error querying url: " + urlString, e);
} finally {
    IoUtil.close(inputStream);
    IoUtil.close(outputStreamWriter);
    IoUtil.close(outputStream);
}
connectexception urlconnection connection java
10 Answers

Connection timeouts (assuming a local network and several client machines) typically result from

a) some kind of firewall on the way that simply eats the packets without telling the sender things like "No Route to host"

b) packet loss due to wrong network configuration or line overload

c) too many requests overloading the server

d) a small number of simultaneously available threads/processes on the server which leads to all of them being taken. This happens especially with requests that take a long time to run and may combine with c).

Hope this helps.

Jumpy_94160

If the URL works fine in the web browser on the same machine, it might be that the Java code isn't using the HTTP proxy the browser is using for connecting to the URL.

Alexander_167240

I'd recommend raising the connection timeout time before getting the output stream, like so:

urlConnection.setConnectTimeout(1000);

Where 1000 is in milliseconds (1000 milliseconds = 1 second).

R_Bemrose_158800
  • try to do the Telnet to see any firewall issue
  • perform tracert/traceroute to find number of hops
Admin1

Why would a “java.net.ConnectException: Connection timed out” exception occur when URL is up?

Because the URLConnection (HttpURLConnection/HttpsURLConnection) is erratic. You can read about this here and here. Our solution were two things:

a) set the ContentLength via setFixedLengthStreamingMode

b) catch any TimeoutException and retry if it failed.

user_23115280

There is a possibility that your IP/host are blocked by the remote host, especially if it thinks you are hitting it too hard.

larsivi_140470
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