OSGi¶

Using the shaded jar¶

java-driver-core-shaded shares the same bundle name as java-driver-core (com.datastax.oss.driver.core). It can be used as a drop-in replacement in cases where you have an explicit version of dependency in your project different than that of the driver’s. Refer to shaded jar for more information.

Using a custom ClassLoader¶

In several places of the driver configuration it is possible to specify the class name of something to be instantiated by the driver such as the reconnection policy. This is accomplished using reflection, which uses a ClassLoader. By default, the driver uses its own bundle’s ClassLoader to instantiate classes by reflection. This is typically adequate as long as the driver bundle has access to the bundle where the implementing class resides.

However if the default ClassLoader cannot load the implementing class, you may encounter an error like this:

java.lang.ClassNotFoundException: com.datastax.oss.MyCustomReconnectionPolicy

Similarly, it also happens that the default ClassLoader is able to load the implementing class but is not able to ascertain whether that class implements the expected parent type. In these cases you may encounter an error such as:

java.lang.IllegalArgumentException: Expected class ExponentialReconnectionPolicy
(specified by advanced.reconnection-policy.class) to be a subtype of
com.datastax.oss.driver.api.core.connection.ReconnectionPolicy

This is occurring because there is a disparity in the ClassLoaders used between the driver code and the ClassLoader used to reflectively load the class (in this case, ExponentialReconnectionPolicy).

To overcome these issues, you may specify a ClassLoader instance when constructing a Session by using withClassLoader().

Alternatively, if you have access to the BundleContext (for example, if you are creating the session in an Activator class) you can also obtain the bundle’s ClassLoader the following way:

BundleContext bundleContext = ...;
Bundle bundle = bundleContext.getBundle();
BundleWiring bundleWiring = bundle.adapt(BundleWiring.class);
ClassLoader classLoader = bundleWiring.getClassLoader();
CqlSession session = CqlSession.builder()
    .withClassLoader(classLoader)
    .build();

BundleContext bundleContext = ...;
Bundle bundle = bundleContext.getBundle();
BundleWiring bundleWiring = bundle.adapt(BundleWiring.class);
ClassLoader classLoader = bundleWiring.getClassLoader();

CqlSession session = CqlSession.builder()
    .withClassLoader(classLoader)
    .withConfigLoader(DriverConfigLoader.fromDefaults(classLoader))
    .build();

BundleContext bundleContext = ...;
Bundle bundle = bundleContext.getBundle();
BundleWiring bundleWiring = bundle.adapt(BundleWiring.class);
ClassLoader classLoader = bundleWiring.getClassLoader();
DriverConfigLoader loader =
    DriverConfigLoader.programmaticBuilder(classLoader)
        .withDuration(DefaultDriverOption.REQUEST_TIMEOUT, Duration.ofSeconds(5))
        .startProfile("slow")
        .withDuration(DefaultDriverOption.REQUEST_TIMEOUT, Duration.ofSeconds(30))
        .endProfile()
        .build();
CqlSession session = CqlSession.builder()
    .withClassLoader(classLoader)
    .withConfigLoader(loader)
    .build();

What does the “Error loading libc” DEBUG message mean?¶

The driver is able to perform native system calls through JNR in some cases, for example to achieve microsecond resolution when generating timestamps.

Unfortunately, some of the JNR artifacts available from Maven are not valid OSGi bundles and cannot be used in OSGi applications.

JAVA-1127 has been created to track this issue, and there is currently no simple workaround short of embedding the dependency, which we’ve chosen not to do.

Because native calls are not available, it is also normal to see the following log lines when starting the driver:

[main] DEBUG - Error loading libc
java.lang.NoClassDefFoundError: jnr/ffi/LibraryLoader
...
[main] INFO - Could not access native clock (see debug logs for details), falling back to Java
system clock