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ScyllaDB Java Driver is available under the Apache v2 License. ScyllaDB Java Driver is a fork of DataStax Java Driver. See Copyright here.
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-mapper-runtimejava-driver-core-shaded
Note: some of the driver dependencies are not valid OSGi bundles. Most of them are optional, and the
driver can work properly without them (see the
Integration>Driver dependencies section for more
details); in such cases, the corresponding packages are declared with optional resolution in
Import-Package directives. However, if you need to access such packages in an OSGi container you
MUST wrap the corresponding jar in a valid OSGi bundle and make it available for provisioning to the
OSGi runtime.
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();
Using a custom ClassLoader for application-bundled configuration resources¶
In addition to specifying a ClassLoader when constructing a Session, you can also specify
a ClassLoader instance on certain DriverConfigLoader methods for cases when your OSGi
application bundle provides overrides to driver configuration defaults. This is typically done by
including an application.conf file in your application bundle.
For example, you can use DriverConfigLoader.fromDefaults(ClassLoader) to use the driver’s default configuration mechanism while specifying a different class loader:
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();
The above configuration will look for resources named application.conf inside the application
bundle, using the right class loader for that.
Similarly, if you want to use programmatic configuration in you application bundle, but still
want to be able to provide some configuration in an application.conf file, you can use
DriverConfigLoader.programmaticBuilder(ClassLoader):
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();
The above configuration will honor all programmatic settings, but will look for resources named
application.conf inside the application bundle, using the right class loader for that.
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