Java套接字读取超时，错误后无法读取

Question

I am working on a fix to a Java code, which looks like this -

    connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod(POST);
    connection.setRequestProperty("Content-Type", CONTENT_TYPE);
    connection.setReadTimeout(5 * 60 * 1000);
    connection.setUseCaches(false);
    connection.setDoInput(true);
    connection.setDoOutput(true);

    DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
    wr.writeBytes(parameters);
    wr.flush();
    wr.close();

    in = connection.getInputStream();
    connection = null;

It works fine on small amount of data exchange (including concurrent requests). In cases where the data is large or when there are concurrent requests (for large datas), I get a "java.net.SocketTimeoutException: Read timed out" error. After this error, the program fails to read additional data or cater to additional requests. I have to restart the server (JBoss).

My initial idea was to increase the setReadTimeOut to 15. Doesn't help, still get the error for concurrent requests for large dataset.

What are my other options? How would I recover from a read timeout error?

The above code is using java.net.*.

Appreciate any help..WM

Answer 1

I'm pretty sure it has to do with the DataOutputStream you are using to write the body of the http request. I've never seen anyone doing this with a DataOutputStream.

A DataOutputStream is designed to write primitive java types (int, byte, long, etc) to an OutputStream. When fed with a String, like you are doing, it will take each character (2 bytes), and convert it to a byte, while ignoring the highest byte of the character.

This might work for some characters that don't have their highest 8 bits set, but will surely lead to lost data sooner or later. This could then lead to a http request being sent that specifies a content-length that is different from the length of the actual message body, which will in turn lead to the remote server waiting for more data that will never be received.

I would replace the DataOutputStream with eg a BufferedWriter, which allows you to write character data. Also consider using apache's HttpClient, which is far more sophisticated that java's HttpUrlConnection.

Cheers, Tom