Admittedly, this borders on being off-topic (since its more about URLConnections
than about servlets), but there are servlets lurking around on the periphery so
hopefully you'll bear with me. :)
I'm communicating with servlets on a remote machine using URLConnections.
Specifically, I use the following method where urlString points to a servlet
and formData contains the name/value pairs which are posted to the servlet.
========
private static InputStream getInputStream(String urlString, Properties formData )
throws java.net.MalformedURLException, java.io.IOException {
// Build the content to be posted
ByteArrayOutputStream content = new ByteArrayOutputStream();
String theName = "";
String theValue = "";
String connector = "";
if (formData != null) {
for (Enumeration e = formData.propertyNames(); e.hasMoreElements();) {
theName = (String)e.nextElement();
theValue = URLEncoder.encode(formData.getProperty(theName));
StringUtil.write(content,connector + theName + "=" + theValue);
connector = "&";
}
}
byte[] content_bytes = content.toByteArray();
int content_length = content_bytes.length;
content.close();
// Post the content to the URL.
URL url = new URL(urlString);
URLConnection urlConnection = url.openConnection();
urlConnection.setAllowUserInteraction(true);
urlConnection.setDoInput(true);
urlConnection.setDoOutput(true);
urlConnection.setRequestProperty("User-Agent","MyUserAgent");
urlConnection.setRequestProperty("Content-type","application/x-www-form-urlencoded");
urlConnection.setRequestProperty("Content-length", String.valueOf(content_length));
// Grab the OutputStream.
OutputStream outputStream = urlConnection.getOutputStream();
outputStream.write(content_bytes);
outputStream.close();
// Return the InputStream
return urlConnection.getInputStream(); // This is line 162 in NetUtil.java (see
below)
}
=============
Most of the time (more than 99%), this works just fine. However, occasionally,
this method throws a FileNotFoundException at the last line where it tries
to get the InputStream from the urlConnection. For example:
java.io.FileNotFoundException: http://the.remote.host/servlets/RemoteServlet
at
sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:485)
at ImageCafe.lib.NetUtil.getInputStream(NetUtil.java:162)
at ImageCafe.lib.NetUtil.postRequest(NetUtil.java:82)
...
First of all, I'm confused because this is happening in a place in the code after I've
already successfully written to an OutputStream connected to the RemoteServlet
so I didn't expect there to be problems when I grab the resulting InputStream.
I'm hoping that someone with a better understanding of URLConnections could
explain what might be going on behind the scenes which would cause this.
Secondly, if it does turn out that there is nothing that I can do to prevent this
from happening, what might I do to recover gracefully? Should I catch the
exception and try again (say 3 times). Might it help to throw in a Thread.sleep?
Any suggestions would be greatly appreciated.
Thanks,
John
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