JarCastingkcqrs
CQRS library build in Kotlin for better development experience.
Build Status
Architecture
Use Case
class Invoice private constructor(@JvmField var customerName: String, @JvmField val amount: BigDecimal) : AggregateRootBase() {
// Required for the serialization
constructor() : this("", BigDecimal.ZERO)
constructor(id: UUID, customerName: String, amount: BigDecimal) : this(customerName, amount) {
applyChange(InvoiceCreatedEvent(id, customerName))
}
fun changeCustomerName(customerName: String) {
applyChange(InvoiceCustomerNameChangedEvent(getId()!!, customerName))
}
fun apply(event: InvoiceCreatedEvent) {
uuid = event.invoiceId
customerName = event.customerName
}
fun apply(event: InvoiceCustomerNameChangedEvent) {
customerName = event.newCustomerName
}
}
data class InvoiceCreatedEvent(@JvmField val invoiceId: UUID, @JvmField val customerName: String) : Event
data class InvoiceCustomerNameChangedEvent(@JvmField val invoiceId: UUID, @JvmField val newCustomerName: String) : Event
// ...
// Usage
val invoice = Invoice(UUID.randomUUID(), "John", BigDecimal(30))
eventRepository.save(invoice)
invoice.changeCustomerName("Peter")
eventRepository.save(invoice)
// Load Invoice document from events
val updateInvoice = eventRepository.getById(invoice.getId()!!, Invoice::class.java)
Handling Commands
val messageBus = cqrs.messageBus()
// On App Initialization
messageBus.registerCommandHandler(ChangeCustomerName::class.java, ChangeCustomerNameHandler())
// Dispatch User Action in Servlet or REST Api Call
fun registerNewCustomer(req: HttpServletRequest, HttpServletResponse) {
msgBus.send(RegisterNewCustomer(req.getParameter("name")))
}
Handling Events
val messageBus = cqrs.messageBus()
// On App Initialization
msgBus.registerEventHandler(CustomerRegisteredEvent::class.java, CustomerRegisteredEventHandler(InMemoryCustomerRepository()))
// Handle registration event
msgBus.handle(CustomerRegisteredEvent("Any Customer Name"))
Interceptors
Interceptors are a powerful mechanism that can monitor, rewrite, and retry calls. Here's a simple interceptor that publishes received event.
val msgBus = cqrs.messageBus()
val pubSubPublisher = object : Interceptor {
override fun intercept(chain: Interceptor.Chain) {
// make sure that event is processed by other handlers
chain.proceed(chain.event())
val pubSubEvent = adapt(chain.event())
pubSubPublisher.publish(pubSubEvent)
}
}
msgBus.registerInterceptor(pubSubPublisher)
// ....
msgBus.handle(event)
App Engine Adapter
Registering Event Handler
class KCqrsEventHandler : AbstractEventHandlerServlet() {
private val gson = Gson()
override fun decode(inputStream: InputStream, type: Class<*>): Event {
val event = gson.fromJson(InputStreamReader(inputStream, "UTF-8"), type)
return event as Event
}
override fun messageBus(): MessageBus {
return CQRSContext.messageBus()
}
}
Adding it to web.xml
<servlet>
<servlet-name>kcqrsEventHandler</servlet-name>
<servlet-class>com.clouway.kcqrs.example.KCqrsEventHandler</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>kcqrsEventHandler</servlet-name>
<url-pattern>/worker/kcqrs</url-pattern>
</servlet-mapping>
<security-constraint>
<web-resource-collection>
<web-resource-name>worker</web-resource-name>
<url-pattern>/worker/*</url-pattern>
</web-resource-collection>
<auth-constraint>
<role-name>admin</role-name>
</auth-constraint>
</security-constraint>
// Initialize KCQRS for GAE
private var cqrs = AppEngineKcqrs.Builder(configuration, messageFormatFactory).build {
kind = "Event"
kcqrsHandlerEndpoint = "/worker/kcqrs"
identityProvider = IdentityProvider.Default()
requestInitializer = HttpRequestInitializer {
it.headers.setAuthorization("Bearer ${securityProvider.getAuthorizationToken()}")
}
}
// Accessing message bus
cqrs.messageBus()
// Accessing repository
cqrs.repository()
Maven dependency
<dependency>
<groupId>com.clouway.kcqrs</groupId>
<artifactId>kcqrs-core</artifactId>
<version>0.0.1</version>
</dependency>
<dependency>
<groupId>com.clouway.kcqrs.adapters</groupId>
<artifactId>kcqrs-appengine</artifactId>
<version>0.0.1</version>
</dependency>
TODO
- MongoDB Adapter
License
Copyright 2018 clouWay ood.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
https://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
