Re: NullPointerException at listFiles

2012/3/5 Michael B Allen <[email protected]>

>
> Hi Gabor,
>
> I don't think it's a good idea to set the tconHostName in the constructor.
>
> Please post the full NPE stack trace.
>
> Mike
>
>
Hi Mike,

the stack trace is exactly the same as reported by Dora:

*java.lang.NullPointerException*
        at jcifs.smb.Dfs.resolve(*Dfs.java:169*)
        at jcifs.smb.SmbFile.resolveDfs(*SmbFile.java:671*)
        at jcifs.smb.SmbFile.send(*SmbFile.java:773*)
        at jcifs.smb.SmbFile.doFindFirstNext(*SmbFile.java:1986*)
        at jcifs.smb.SmbFile.doEnum(*SmbFile.java:1738*)
        at jcifs.smb.SmbFile.listFiles(*SmbFile.java:1715*)
        at jcifs.smb.SmbFile.listFiles(*SmbFile.java:1648*)
        at Test$Browser.run(*Test.java:25*)
        at java.lang.Thread.run(*Thread.java:662*)

At first we only changed the finally block, but that did not fix the
problem. Only after setting tconHostName in the constructor jcifs was able
to recover from a temporary connection loss. We use the following test code
to reproduce the problem:

Test.java:
---------------------------------------------------------------------------------------------------------------------------------------------------------------
import jcifs.smb.NtlmPasswordAuthentication;
import jcifs.smb.SmbFile;


public class Test {

        public class Browser implements Runnable {

                private int id;

                public Browser(int n) {
                        id = n;
                }

                @Override
                public void run() {
                        for (int n = 0; n < 1000; n++) {
                                NtlmPasswordAuthentication auth = new
NtlmPasswordAuthentication("domain", "user", "passwd");

                                try {
                                        System.out.println("Thread " + id +
" browsing folder.");

                                        SmbFile file = new
SmbFile("smb://server/dir/", auth);

                                        file.listFiles();
                                } catch (Exception e) {
                                        e.printStackTrace();
                                }
                        }
                }
        }

        public static void main(String[] args) {
                new Test().run();
        }

        public void run() {
                try {
                        jcifs.Config.setProperty( "jcifs.netbios.wins",
"XX.XX.XX.XX" );

                        for (int n = 0; n < 50; n++) {
                                new Thread(new Browser(n)).start();
                                Thread.sleep(200);
                        }
                } catch (Exception e) {
                        e.printStackTrace();
                }
        }
}
-------------------------------------------------------------------------------------------------------------------------------------------------------------

The multiple theads are needed to create a significant load. While the test
case is running, we simulate a network error by simply pulling the network
cable and reconnect it again. Without the changes I've posted jcifs cannot
recover and persistently throws NPEs at Dfs.resolve, because tconHostName
is null. With both changes applied, the connection is recovered and no
exception is thrown, no matter how often we interrupt the connection.

Setting tconHostName in the constructor ensures, that it is matching the IP
address, which is also stored there. In a reconnect attempt the host name
is not passed in, that's why the error occurs.