This repo is a demonstration of the problem that occurs with the Sybase JDBC
driver when running under Java 9. The Sybase driver is closed source and
can't be redistributed, so this includes a simple implementation of
java.sql.Driver for illustration.
The dummy driver CircularDriver has a static initializer which instantiates a
new CircularDriver. The CircularDriver constructor calls
registerWithDriverManager(), which iterates through the drivers available to
DriverManager and tries to remove any other CircularDriver instances that
are not the current instance.
The problem is that, in Java 9, DriverManager uses ServiceLoader to load and
instantiate drivers. So the constructor of CircularDriver calls
DriverManager.getDrivers(), which uses ServiceLoader to find all drivers,
which instantiates a new CircularDriver, which calls back to
DriverManager.getDrivers(), and so on.
In normal circumstances, we can't easily modify the Sybase driver directly, so
the solution is to use ByteBuddy to rewrite the class at
runtime to skip registerWithDriverManager(). This prevents the loop of
loading.
The test runner can run with ByteBuddy off, to illustrate the problem, or with
ByteBuddy on to demonstrate that the solution works. Since the test has to do
with class loading, trying to run both versions in the same JVM could cause them
to interfere with each other. After CircularDriver is loaded, even without the
fix, things will work normally.
First, compile the code:
mvn compile
Then run the sample as:
mvn exec:exec -DuseByteBuddy=true
to run with ByteBuddy (the default) or
mvn exec:exec -DuseByteBuddy=false
to run without the ByteBuddy fix.
The "failing" case will produce hundreds of lines like this:
registerDriver: com.example.circular.jdbc.CircularDriver@1bce4f0a
Calling registerWithDriverManager() for com.example.circular.jdbc.CircularDriver@5e3a8624
as well as
DriverManager.initialize: jdbc.drivers = null
JDBC DriverManager initialized
Make sure you are running under Java 9 if -DuseByteBuddy=false does not
produce the error output.