Sunday, August 05, 2007

Mulgara on Java 6

I'm nearly at the point where I can announce that Mulgara runs on Java 6 (or JDK 1.6). Many of the problems were due to tests looking for an exact output, while the new hashtables iterate over their data in a different order.

The remaining problems fall into two areas.

The first seems to be internal to the implementation of the Java 6 libraries. In one case the HTTPS connection code is unable to find an internal class that occurs in the same place for both Java 5 and Java 6. In another case, a method whose javadoc explicitly says will contain no caching, claims that it has "already closed the file" for all but the first time you try to open a JAR file using a URL, even though the URL object is newly created for each attempt.

These problems may involve some browsing of Java source code to properly track down. Fortunately, they only show up in rarely-used resolver modules (I've never used them myself).

The other problem is that as of Java 6, the java.sql.ResultSet interface has a new series of methods on it. I'd rather that we didn't, but we implement this interface with one of our classes. This is a holdover from a time when we tried to implement JDBC. While it mostly worked, there was a fundamental disconnect with the metadata requirements of JDBC, and so we eventually abandoned the interface. However, the internal implementation of this interface remains.

Since we don't use any of the new methods, then it is a trivial matter to implement these methods with empty stubs. Eclipse does this with a couple of clicks, so it was very easy to do. Once this was done, the project compiled fine, and I could get onto tracking down the failures and errors in the tests, the causes of which I've described above.

All this was going well, until someone pointed out that there were some issues under Windows. After spending some time getting the OS up and running again, I quickly found that the class implementing ResultSet was missing some methods. How could this be? It had all the methods on OS X.

The simple answer is to run javap on the java.sql.ResultSet interface, and compare the results. Sure enough, on Windows (and Linux) the output contains 14 entries not found in OS X!


This is easy enough to fix. Implementing the methods with stubs will make it work on Linux and Windows, and will have no effect on OS X. But why the difference? This meets my definition of broken.

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