Esper-8 Migrating Step-By-Step For Existing Applications

The instructions herein are meant to be used together with the remaining material on migrating. They provide an outline for moving an application to Esper 8.

Classpath Changes

Remove CGLib from classpath. Add the Esper compiler, common and runtime jar files and their dependencies.

Configuration Changes

Please see the document on migrating configuration XML and configuration code.

The following settings are for applications that allow subscribers and that rely on the Esper-7 global public visibilities.

The XML configuration is:

<esper-configuration xmlns="https://www.espertech.com/schema/esper">
    <compiler>
		<bytecode
                allow-subscriber="true"
                access-modifier-context="public"
                access-modifier-event-type="public"
                access-modifier-expression="public"
                access-modifier-named-window="public"
                access-modifier-script="public"
                access-modifier-table="public"
                access-modifier-variable="public"
                bus-modifier-event-type="bus"/>
    </compiler>
</esper-configuration>

The code for using the configuration API is:

Configuration configuration = new Configuration();
configuration.getCompiler().getByteCode().setAllowSubscriber(true);
configuration.getCompiler().getByteCode().setAccessModifiersPublic();
configuration.getCompiler().getByteCode().setBusModifierEventType(EventTypeBusModifier.BUS);

By setting the allow-subscriber flag your statement allows subscribers to receive results. Esper-7 allows subscribers by default.

By setting the default access modifiers to PUBLIC all EPL-objects such as event types are publicly visible. Esper-7 has only public visibility.

By setting the bus-modifier for event types to BUS your application can use send-event to send any type of event into the engine. Esper-7 has only bus visibility.

Remove Esper-related Imports from Classes

All package names have changed due to the refactoring into common, compiler and runtime. Please remove all Esper-related imports from the import section of each class.

Classes in com.espertech.esper.client that were common to the compiler and runtime have been moved to com.espertech.esper.common.client, for example EventBean and EventType.

Classes in com.espertech.esper.client that were specific to the runtime have been moved to com.espertech.esper.runtime.client.

Compile-Related Changes

Esper-8 uses a compiler for compiling an EPL module to byte code. The Esper-7 createEPL method has been removed. You could use the utility method shown below for compiling. It returns you a Deployment object. Use deployment.getStatements() to obtain the EPStatement instances.

Here is a method that can replace createEPL calls of Esper-7:

public static EPDeployment compileDeploy(EPRuntime runtime, String epl) {
  try {
    // Obtain a copy of the engine configuration
    Configuration configuration = runtime.getConfigurationDeepCopy();

    // Build compiler arguments
    CompilerArguments args = new CompilerArguments(configuration);

    // Make the existing EPL objects available to the compiler
    args.getPath().add(runtime.getRuntimePath());

    // Compile
    EPCompiled compiled = EPCompilerProvider.getCompiler().compile(epl, args);

    // Return the deployment
    return runtime.getDeploymentService().deploy(compiled);
  }
  catch (Exception ex) {
    throw new RuntimeException(ex);
  }
}

Here is how to use the method above:

EPDeployment deployment = compileDeploy(runtime, epl);
deployment.getStatements()[0].addListener(...);

Change Listener Code

The StatementAwareUpdateListener interface has been removed. Instead the UpdateListener interface was changed to match the StatementAwareUpdateListener
footprint.

Change Calls to the `EPRuntime#sendEvent` method

The send-event and route-event methods were moved to the EPEventService interface and were renamed to consistently account for the underlying event object
to be processed. All methods now also require the event type name as a parameter. The new methods are sendEventBean, sendEventMap, sendEventObjectArray,
sendEventXMLDOM and sendEventAvro.

For example:

runtime.getEventService().sendEventBean(new MyEvent(...), "MyEvent");

Change Code That Advances Time

The TimerEvent class is removed and the sendEvent method can no longer be used to advance time. Use EPEventService#advanceTime(time) and EPEventService#clockExternal() instead.

Change Code That Uses the Runtime Configuration API

The ConfigurationOperations interface has been removed. Instead use the Configuration interface or respective service such as EPVariableService.

Esper-8 Migrating Step-By-Step For Existing Applications