OSGi
The driver is available as an OSGi bundle. More specifically, the following maven artifacts are valid OSGi bundles:
java-driver-corejava-driver-query-builderjava-driver-core-shaded
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 Thread.currentThread
.getContextClassLoader() if available, otherwise it uses its own ClassLoader. This is typically
adequate except in environments like application containers or OSGi frameworks where class loading
logic is much more deliberate and libraries are isolated from each other.
If the chosen ClassLoader is not able to ascertain whether a loaded class is the same instance
as its expected parent type, 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).
You may also encounter ClassNotFoundException if the ClassLoader does not have access to the
class being loaded.
To overcome these issues, you may specify a ClassLoader instance when constructing a Session
by using withClassLoader(). In a lot of cases, it may be adequate to pass in the ClassLoader
from a Class that is part of the core driver, i.e.:
CqlSession session = CqlSession.builder()
.withClassLoader(CqlSession.class.getClassLoader())
.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