How can I tell why I'm getting an IOException at line 113 in com.sun.jdmk.comm.HttpSendSocket

Question

My JDMK based application is getting intermittent IOExceptions at line 313 in com.sun.jdmk.comm.HttpSendSocket and I can't figure out why. All I know from the Javadoc about this is if an I/O error occurs while creating the input stream you'll get an IOException, but I don't know what kind of I/O error occurred or why one did. The code actually worked both before and after this error transpired.

Any tips on how to debug this intermittent problem would be appreciated.

I don't want to paste the source code here for HttpSendSocket since it belongs not to me, but I know it's doing an HttpURLConnection conn.getInputStream() when the IOException exception is thrown.

I thought about trying to create my own version of HttpSendSocket, and adding diagnostics in it, but couldn't figure out how since it's a package protected class.

Stack trace below:

com.sun.jdmk.comm.CommunicationException: java.io.IOException: HTTP request failed
at com.sun.jdmk.comm.HttpSendSocket.readNotify(HttpSendSocket.java:313)
at com.sun.jdmk.comm.HttpSendInputStream.read(HttpSendInputStream.java:95)
at java.io.FilterInputStream.read(FilterInputStream.java:94)
at java.io.PushbackInputStream.read(PushbackInputStream.java:150)
at com.sun.jdmk.comm.GenericHttpConnectorClient.sendHttp(GenericHttpConnectorClient.java:486)
at com.sun.jdmk.comm.GenericHttpConnectorClient.invokeRemoteOperation(GenericHttpConnectorClient.java:2234)
at com.sun.jdmk.comm.GenericHttpConnectorClient.invoke(GenericHttpConnectorClient.java:1366)

As I said, any helpful suggestions would be appreciated.

Answer 1

The communication Exception was caused by using ArrayList method subList. ArrayList is serializable but subList data IS NOT serializable, and therefore you cannot retrieve the data over an HttpConnector. The solution was to change:

List<UserProcessInfo> values = new ArrayList<UserProcessInfo>();
...
values.size() <= 1000 ? values : values.subList(0,1000);

to:

List<UserProcessInfo> values = new ArrayList<UserProcessInfo>();
...
return values.size() <= 1000 ? values : new ArrayList<UserProcessInfo>(values.subList(0,1000));

Answer 2

Attach the JDMK source to your IDE, then set a breakpoint in the HttpSendSocket and run it with debugging enabled. At least in IntelliJ you can attach the library source by trying to open the class from the stacktrace, then choosing to link source. Don't know how the process is for other IDE's but I would expect it to be possible.