db4o at Honeycomb and Ice Cream Sandwich – UPDATE

Did you receive a NetworkOnMainThreadException while opening a new db4o database?

Since my last post I just worked with Andorid 2.x on which I could get db4o easily to run. When I wanted to run my db4o app at Android Honeycomb I received the NetworkOnMainThreadException exception.

Google introduced with Honeycomb the Android.os.NetworkOnMainThreadException which occurs when an application attempts to perform a networking operation on it’s main thread (see here). This doesn’t sound like it matters for a database environment. But that’s exactly what happens when I call

Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), dbPath);

for the first time. Just for the first time because it seems that when db4o creates a new db file it generates it’s unique internal signature by calling java.net.InetAddress.getLocalHost().getHostName(). Because java.net belongs to the network classes the exception java.net.InetAddress.lookupHostByName(InetAddress.java:477) is thrown.

Here is the piece of db4o code which causes the exception:

try {
  String hostName = java.net.InetAddress.getLocalHost().getHostName() + "_";
    if(hostName.length() > 15){
      hostName = hostName.substring(0,15);
    }
  sb.append(hostName);
} catch (UnknownHostException e) {
}
sb.append(Long.toHexString(System.currentTimeMillis()));
sb.append(Integer.toHexString(_counter++));
int hostAddress = 0;
byte[] addressBytes;
try {
  addressBytes = java.net.InetAddress.getLocalHost().getAddress();
  for (int i = 0; i < addressBytes.length; i++) {
    hostAddress <<= 4;
    hostAddress -= addressBytes[i];
  }
} catch (UnknownHostException e) {
}

A workaround is to just catch the NetworkOnMainThreadException (okay, then it’s a android specific jar) or change the UnknownHostException to a generic Exception. This is kind of dirty but if nothing happens within the the catch it doesn’t matter anyways.

Another aproach would be to to preform the first call for opening a new db not into the UI Thread. A possibility could be to use the AsyncTask:

class OpendDBTask extends AsyncTask<Void, Void, ObjectContainer>{

   @Override
   protected ObjectContainer doInBackground(Void... params) {
      String dbPath = "/data/data/" + DBManager.getPackageName() + "/database";
      ObjectContainer db = Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), dbPath);
      return db;
   }
}

Maybe I’ll provide a android database manager framework for db4o later. If you want to try db4o check out this post.

A bug entry has been created and it seems that it is fixed now. I didn’t retest yet.

Once again I would like to point out that this issue only occurs when a new db is created via “Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), dbPath);” at Android Honeycomb or later!

Cheers, mavi