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API reference - Event Handler API

In most cases, you will create Event Handlers in a kts file using GPAL. This offers a method with succinct code and a good degree of flexibility.

However, you can also implement Event Handlers as a set of classes. Typically, this is useful where you have a complex requirement for business logic and database interaction. For example, a kts file of 1,000 lines is difficult to test and maintain; in this case, a set of individual classes is much more convenient.

For implementing an Event Handler as a set of classes, there are three different options:

Async. This uses the Kotlin coroutine API to simplify asynchronous development. This is the underlying implementation used in GPAL Event Handlers. You can only create Async Event Handlers using Kotlin.
RxJava3. This uses the RxJava3 library, which is a popular option for composing asynchronous event-based programs. You can create RxJava3 Event Handlers using either Kotlin or Java.
Sync. This creates synchronous Event Handlers. You can create Sync Event Handlers using either Kotlin or Java.

note

Java Event Handlers can be implemented using RxJava3 and Sync Event Handlers only. Async Event Handlers cannot be used, as there is no implementation for Kotlin coroutines in Java.

We recommend using Kotlin to implement Event Handlers.

Configure in processes.xml file

You need to add the global.genesis.eventhandler package to the package tag of the process; this tag defines which package the process should refer to. For example:

<process name="POSITION_NEW_PROCESS">    
    <groupId>POSITION</groupId>    
    <start>true</start>    
    <options>-Xmx256m -DRedirectStreamsToLog=true -DXSD_VALIDATE=false</options>    <module>position-new-process</module>    
    <package>global.genesis.eventhandler,position.company.manager</package>    <description>Handles events</description>  
</process>

Event Handler interface

The Event Handler interface is the common supertype of AsyncEventHandler, Rx3EventHandler and SyncEventHandler, but it is not meant to be used on its own. It provides basic options for each Event Handler definition, which can be overridden. See the Kotlin methods explanation below:

Name	Signature	Default value	Description
excludeMetadataFields	`fun excludeMetadataFields(): Set<String>`	setOf("RECORD_ID", "TIMESTAMP")	Contains a list of metadata fields to be excluded from the event metadata extracted from the input `I`
includeMetadataFields	`fun includeMetadataFields(): Set<String>`	emptySet()	Contains a list of metadata fields that need to be included in the event metadata; this must be available in input `I`. A non-empty list will exclude the other fields.
messageType	`fun messageType(): String?`	null	Contains the name of the Event Handler. If undefined, the Event Handler name will become `EVENT_INPUT_CLASS_NAME`. So, for an Event Handler using an input type called `TradeInsert`, the message type will become `EVENT_TRADE_INSERT`.
overrideMetadataFields	`fun overrideMetadataFields(): Map<String, OverrideMetaField>`	emptySet()	Contains a map (key-value entries) of metadata field names to metadata field definitions in the shape of `OverrideMetaField`. This enables you to override the metadata field properties extracted from input `I`
requiresPendingApproval	`fun requiresPendingApproval(): Boolean`	false	This is used where particular system events require a second system user to approve them (pending approval in order to take effect)
schemaValidation	`fun schemaValidation(): Boolean`	true	This option enables you to disable the automatic Json Schema validation enforced by the back end. See type-safe messages for more information.

Each custom Event Handler must define an input message type I and an output message type O (these need to be data classes), as GPAL Event Handlers do). In the examples below, Company is the input message and EventReply is the output message. The message object contains event message and has the following properties :

Name	Default value	Description
details		This has input information, example: Company
messageType		Name of the Event Handler
userName		Name of logged-in user
ignoreWarnings	false	If set to false, events will not be processed if there are any warnings; you will get EventNack with warning message. If set to true, warning messages will be ignored; processing of events will be stopped only if there are any errors
requiresApproval	false	This particular event needs approval from a second user if set to true. For more details, check Pending Approval
approvalKey	null	Auto-generated key ID for particular approval request. For more details, check Pending Approval
approvalMessage	null	Optional message for approval request. For more details, check Pending Approval
reason	null	Optional reason sent as part of event message

Inject objects

Use @Inject to provide instances for any objects needed as part of the dependency injection stage

Async

AsyncEventHandler

This is the most basic definition of an Async Event Handler. You can define an AsyncEventHandler by implementing the AsyncEventHandler interface, which is defined as: interface AsyncEventHandler : AsyncEventWorkflowProcessor<I, O>, EventHandler

The only mandatory method to implement this in the interface is:

Name	Signature
process	`fun suspend process(message: Event<I>) : O`

This method passes the input message type I as a parameter and expects the output message type O to be returned.

Here is an example:

import com.google.inject.Inject
import global.genesis.commons.annotation.Module
import global.genesis.db.rx.entity.multi.AsyncEntityDb
import global.genesis.eventhandler.typed.async.AsyncEventHandler
import global.genesis.gen.dao.Company
import global.genesis.message.core.event.Event
import global.genesis.message.core.event.EventReply

@Moduleclass EventCompanyHandlerAsync @Inject constructor(        
    private val entityDb: AsyncEntityDb,        
    private val companyService: CompanyService
) : AsyncEventHandler<Company, EventReply> {   
    override suspend fun process(message: Event<Company>): EventReply {       
        val company = message.details        
        // custom code block..        
        return EventReply.EventAck()    
    }
}

The methods below are provided as part of AsyncEventHandler; they provide an easy way of creating EventReply responses.

Name	Signature
ack	`fun <I : Any> AsyncEventHandler<I, EventReply>.ack(): EventReply`
ack	`fun <I : Any> AsyncEventHandler<I, EventReply>.ack(generated: List<Map<String, Any>> = emptyList()): EventReply`
nack	`fun <I : Any> AsyncEventHandler<I, EventReply>.nack(throwable: Throwable): EventReply`
nack	`fun <I : Any> AsyncEventHandler<I, EventReply>.nack(error: String): EventReply`

Using these helper methods, you could simplify the previous implementation like this:

import global.genesis.commons.annotation.Module
import global.genesis.eventhandler.typed.async.AsyncEventHandler
import global.genesis.message.core.event.Event
import global.genesis.message.core.event.EventReply

@Module
class EventCompanyHandlerAsync : AsyncEventHandler<Company, EventReply> {    
    override suspend fun process(message: Event<Company>): EventReply {        
        val company = message.details        
        // custom code block..        
        return ack()    
    }
}

AsyncValidatingEventHandler

In the previous example, there was no distinction between validation and commit blocks, which is possible in GPAL Event Handlers. In order to have a better separation of concerns using custom Event Handlers, you can implement the AsyncValidatingEventHandler interface, which is defined as:

interface AsyncValidatingEventHandler : AsyncEventHandler<I, O>

Implementation

Using this interface, you do not need to override the process method; you can split your logic into validation and commit stages. There are various methods of implementing this, which are described below:

Name	Signature
onValidate	`suspend fun onValidate(message: Event<I>): O`
onCommit	`suspend fun onCommit(message: Event<I>): O`

Here is an example:

import global.genesis.commons.annotation.Module
import global.genesis.eventhandler.typed.async.AsyncValidatingEventHandler
import global.genesis.message.core.event.Event
import global.genesis.message.core.event.EventReply

@Module
class TestCompanyHandlerAsync : AsyncValidatingEventHandler<Company, EventReply> {
    override suspend fun onValidate(message: Event<Company>): EventReply {        
        val company = message.details        
        // custom code block..        
        return ack()    
    }    
    
    override suspend fun onCommit(message: Event<Company>): EventReply {        
        val company = message.details        
        // custom code block..        
        return ack()    
    }
}

If the validate flag is received as true, only the onValidate code block will be executed. If the validate flag is received as false, both the onValidate and onCommit blocks will be executed.

AsyncContextValidatingEventHandler

In some cases, you might want to carry information from the onValidate code block to the onCommit code block for efficiency purposes. (For example, if several database look-ups happen in onValidate and you want to reuse that information.) Using the AsyncContextValidatingEventHandler interface, you can provide this context information from the validation stage to the commit stage. See the interface below: interface AsyncContextValidatingEventHandler : AsyncEventHandler<I, O>

Implementation[]

As with the previous example, when using this interface, you do not need to override the process method. The different methods for implementing this are described below:

Name	Signature
onValidate	`suspend fun onValidate(message: Event<I>): ValidationResult<O, C>`
onCommit	`suspend fun onCommit(message: Event<I>, context: C?): O`

The validationResult methods are provided to help with the context creation:

Name	Signature
validationResult	`fun validationResult(result: O): ValidationResult<O, C>`
validationResult	`fun validationResult(result: O, context: C): ValidationResult<O, C>`

The type C represents the contextual information we want to provide, and it can be any Java/Kotlin type. Here is an example:

import global.genesis.commons.annotation.Module
import global.genesis.eventhandler.typed.async.AsyncContextValidatingEventHandler
import global.genesis.message.core.event.Event
import global.genesis.message.core.event.EventReply
import global.genesis.message.core.event.ValidationResult

@Module
class TestCompanyHandlerAsync : AsyncContextValidatingEventHandler<Company, EventReply, String> {    
    override suspend fun onValidate(message: Event<Company>): ValidationResult<EventReply, String> {        
        val company = message.details        
        // custom code block..        
        val companyName = company.companyName        
        return validationResult(ack(), companyName)    
    }    
    
    override suspend fun onCommit(message: Event<Company>, context: String?): EventReply {        
        if(context != null) {            
            // Do something with the context        
        }        
        val company = message.details        
        // custom code block..        
        return ack()    
    }
}

Rx3

The mechanism explained in Async can be recycled and reapplied in Rx3 Event Handlers.

Rx3EventHandler

In a similar fashion to AsyncEventHandler, there is an Rx3 implementation flavour. It works in a very similar way to AsyncEventHandler, but requires different return types (i.e. we expect to return RxJava3 Single<O> type, instead of just the O type).

See the interface definition below: interface Rx3EventHandler : Rx3EventWorkflowProcessor<I, O>, EventHandler

Implementation

The mandatory method for implementing this is:

Name	Signature
process	`fun process(message: Event<I>) : Single<O>`

Helper methods

Name	Signature
ack	`fun <I : Any> Rx3EventHandler<I, EventReply>.ack(): Single<EventReply>`
ack	`fun <I : Any> Rx3EventHandler<I, EventReply>.ack(generated: List<Map<String, Any>> = emptyList()): Single<EventReply>`
nack	`fun <I : Any> Rx3EventHandler<I, EventReply>.nack(throwable: Throwable): Single<EventReply>`
nack	`fun <I : Any> Rx3EventHandler<I, EventReply>.nack(error: String): Single<EventReply>`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.rx3.Rx3EventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply
    import io.reactivex.rxjava3.core.Single

    @Module
    class TestCompanyHandlerRx3 : Rx3EventHandler<Company, EventReply> {
        override fun process(message: Event<Company>): Single<EventReply> {
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.rx3.Rx3EventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;
    import io.reactivex.rxjava3.core.Single;

    @Module
    public class TestCompanyHandlerRx3 implements Rx3EventHandler<Company, EventReply> {
        @Override
        public Single<EventReply> process(Event<Company> companyEvent) {
            // custom block
            return Single.just(new EventReply.EventAck());
        }
    }

Rx3ValidatingEventHandler

The same applies to an Rx3ValidatingEventHandler. It is similar to AsyncValidatingEventHandler in every way, but the return type is still Single<O>.

interface Rx3ValidatingEventHandler : Rx3EventHandler<I, O>

Implementation

Name	Signature
onValidate	`fun onValidate(message: Event<I>): Single<O>`
onCommit	`fun onCommit(message: Event<I>): Single<O>`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.rx3.Rx3ValidatingEventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply
    import io.reactivex.rxjava3.core.Single

    @Module
    class TestCompanyHandlerRx3 : Rx3ValidatingEventHandler<Company, EventReply> {
        override fun onValidate(message: Event<Company>): Single<EventReply> {
            val company = message.details
            // custom code block..
            return ack()
        }

        override fun onCommit(message: Event<Company>): Single<EventReply> {
            val company = message.details
            // custom code block..
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.rx3.Rx3ValidatingEventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;
    import io.reactivex.rxjava3.core.Single;
    import org.jetbrains.annotations.NotNull;

    @Module
    public class TestCompanyHandlerRx3 implements Rx3ValidatingEventHandler<Company, EventReply> {

        @NotNull
        @Override
        public Single<EventReply> onValidate(@NotNull Event<Company> message) {
            Company company = message.getDetails();
            // custom code block..
            return Single.just(new EventReply.EventAck());
        }

        @NotNull
        @Override
        public Single<EventReply> onCommit(@NotNull Event<Company> message) {
            Company company = message.getDetails();
            // custom code block..
            return Single.just(new EventReply.EventAck());
        }
    }

Rx3ContextValidatingEventHandler

And the same goes for Rx3ContextValidatingEventHandler in relation to AsyncContextValidatingEventHandler.

interface Rx3ContextValidatingEventHandler : Rx3EventHandler<I, O>

Implementation

Name	Signature
onValidate	`fun onValidate(message: Event<I>): Single<ValidationResult<O, C>>`
onCommit	`fun onCommit(message: Event<I>, context: C?): Single<O>`

Helper methods

Name	Signature
validationResult	`fun validationResult(result: O): ValidationResult<O, C>`
validationResult	`fun validationResult(result: O, context: C): ValidationResult<O, C>`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.rx3.Rx3ContextValidatingEventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply
    import global.genesis.message.core.event.ValidationResult
    import io.reactivex.rxjava3.core.Single

    @Module
    class TestCompanyHandlerRx3 : Rx3ContextValidatingEventHandler<Company, EventReply, String> {
        override fun onValidate(message: Event<Company>): Single<ValidationResult<EventReply, String>> {
            val company = message.details
            // custom code block..
            val companyName = company.companyName
            return Single.just(validationResult(EventReply.EventAck(), companyName))
        }

        override fun onCommit(message: Event<Company>, context: String?): Single<EventReply> {
            if (context != null) {
            // Do something with the context
            }
            val company = message.details
            // custom code block..
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.rx3.Rx3ContextValidatingEventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;
    import global.genesis.message.core.event.ValidationResult;
    import io.reactivex.rxjava3.core.Single;
    import org.jetbrains.annotations.NotNull;
    import org.jetbrains.annotations.Nullable;

    @Module
    public class TestCompanyHandlerRx3 implements Rx3ContextValidatingEventHandler<Company, EventReply, String> {

        @NotNull
        @Override
        public Single<EventReply> onCommit(@NotNull Event<Company> event, @Nullable String context) {
            if (!context.isEmpty()) {
                // Do something with the context
            }
            Company company = event.getDetails();
            // custom code block..
            return Single.just(new EventReply.EventAck());
        }

        @NotNull
        @Override
        public Single<ValidationResult<EventReply, String>> onValidate(@NotNull Event<Company> event) {
            Company company = event.getDetails();
            // custom code block..
            String companyName = company.getCompanyName();
            return Single.just(validationResult(new EventReply.EventAck(), companyName));
        }
    }

Sync

Sync works similarly to Async and Rx3, but in this case, there is no Single<O> returned and no suspend modifier used for Kotlin coroutines. The expected output of the Event Handler logic is just the O type.

SyncEventHandler

interface SyncEventHandler : SyncEventWorkflowProcessor<I, O>, EventHandler

Implementation

Name	Signature
process	`fun process(message: Event<I>) : O`

Helper methods

Name	Signature
ack	`fun <I : Any> SyncEventHandler<I, EventReply>.ack(): EventReply`
ack	`fun <I : Any> SyncEventHandler<I, EventReply>.ack(generated: List<Map<String, Any>> = emptyList()): EventReply`
nack	`fun <I : Any> SyncEventHandler<I, EventReply>.nack(throwable: Throwable): EventReply`
nack	`fun <I : Any> SyncEventHandler<I, EventReply>.nack(error: String): EventReply`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.sync.SyncEventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply

    @Module
    class TestCompanyHandlerSync : SyncEventHandler<Company, EventReply> {
        override fun process(message: Event<Company>): EventReply {
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.sync.SyncEventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;

    @Module
    public class TestCompanyHandlerSync implements SyncEventHandler<Company, EventReply> {
        @Override
        public EventReply process(Event<Company> companyEvent) {
            // custom code block
            return new EventReply.EventAck();
        }
    }

SyncValidatingEventHandler

interface SyncValidatingEventHandler : SyncEventHandler<I, O>

Implementation

Name	Signature
onValidate	`fun onValidate(message: Event<I>): O`
onCommit	`fun onCommit(message: Event<I>): O`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.sync.SyncValidatingEventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply

    @Module
    class TestCompanyHandlerSync : SyncValidatingEventHandler<Company, EventReply> {
        override fun onValidate(message: Event<Company>): EventReply {
            val company = message.details
            return ack()
        }

        override fun onCommit(message: Event<Company>): EventReply {
            val company = message.details
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.sync.SyncValidatingEventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;
    import org.jetbrains.annotations.NotNull;

    @Module
    public class TestCompanyHandlerSync implements SyncValidatingEventHandler<Company, EventReply> {
        @NotNull
        @Override
        public EventReply onCommit(@NotNull Event<Company> event) {
            Company company = event.getDetails();
            // custom code block
            return new EventReply.EventAck();
        }

        @NotNull
        @Override
        public EventReply onValidate(@NotNull Event<Company> event) {
            Company company = event.getDetails();
            // custom code block
            return new EventReply.EventAck();
        }
    }

SyncContextValidatingEventHandler

interface SyncContextValidatingEventHandler : SyncEventHandler<I, O>

Implementation

Name	Signature
onValidate	`fun onValidate(message: Event<I>): ValidationResult<O, C>`
onCommit	`fun onCommit(message: Event<I>, context: C?): O`

Helper methods

Name	Signature
validationResult	`fun validationResult(result: O): ValidationResult<O, C>`
validationResult	`fun validationResult(result: O, context: C): ValidationResult<O, C>`

Here is an example:

Kotlin
Java

    import global.genesis.commons.annotation.Module
    import global.genesis.eventhandler.typed.sync.SyncContextValidatingEventHandler
    import global.genesis.gen.dao.Company
    import global.genesis.message.core.event.Event
    import global.genesis.message.core.event.EventReply
    import global.genesis.message.core.event.ValidationResult

    @Module
    class TestCompanyHandlerSync : SyncContextValidatingEventHandler<Company, EventReply, String> {
        override fun onValidate(message: Event<Company>): ValidationResult<EventReply, String> {
            val company = message.details
            // custom code block..
            val companyName = company.companyName
            return validationResult(ack(), companyName)
        }

        override fun onCommit(message: Event<Company>, context: String?): EventReply {
            if (context != null) {
                // Do something with the context
            }
            val company = message.details
            // custom code block..
            return ack()
        }
    }

    import global.genesis.commons.annotation.Module;
    import global.genesis.eventhandler.typed.sync.SyncContextValidatingEventHandler;
    import global.genesis.gen.dao.Company;
    import global.genesis.message.core.event.Event;
    import global.genesis.message.core.event.EventReply;
    import global.genesis.message.core.event.ValidationResult;
    import org.jetbrains.annotations.NotNull;
    import org.jetbrains.annotations.Nullable;

    @Module
    public class TestCompanyHandlerSync implements SyncContextValidatingEventHandler<Company, EventReply, String> {

    @NotNull
    @Override
    public ValidationResult<EventReply, String> onValidate(@NotNull Event<Company> event) {
        Company company = event.getDetails();
        // custom code block..
        String companyName = company.getCompanyName();
        return validationResult(new EventReply.EventAck(), companyName);
    }

    @NotNull
    @Override
    public EventReply onCommit(@NotNull Event<Company> event, @Nullable String context) {
        if (!context.isEmpty()) {
        // Do something with the context
        }
        Company company = event.getDetails();
        // custom code block..
        return new EventReply.EventAck();
    }
    }

Configure in processes.xml file​

Event Handler interface​

Inject objects​

Async​

AsyncEventHandler​

AsyncValidatingEventHandler​

Implementation​

AsyncContextValidatingEventHandler​

Implementation[​]​

Rx3​

Rx3EventHandler​

Implementation​

Helper methods​

Rx3ValidatingEventHandler​

Implementation​

Rx3ContextValidatingEventHandler​

Implementation​

Helper methods​

Sync​

SyncEventHandler​

Implementation​

Helper methods​

SyncValidatingEventHandler​

Implementation​

SyncContextValidatingEventHandler​

Implementation​

Helper methods​

Configure in processes.xml file

Event Handler interface

Inject objects

Async

AsyncEventHandler

AsyncValidatingEventHandler

Implementation

AsyncContextValidatingEventHandler

Implementation[]

Rx3

Rx3EventHandler

Implementation

Helper methods

Rx3ValidatingEventHandler

Implementation

Rx3ContextValidatingEventHandler

Implementation

Helper methods

Sync

SyncEventHandler

Implementation

Helper methods

SyncValidatingEventHandler

Implementation

SyncContextValidatingEventHandler

Implementation

Helper methods