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A simple yet 🗲FAST🗲 library to dispatch requests and events to corresponding handlers 🚀
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joel-jeremy/deezpatch
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A simple fast dispatch library.
The library aims to help build applications which apply theCommand Query Responsibility Segregation (CQRS) pattern.
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implementation"io.github.joel-jeremy.deezpatch:deezpatch-core:${version}"<dependency> <groupId>io.github.joel-jeremy.deezpatch</groupId> <artifactId>deezpatch-core</artifactId> <version>${version}</version></dependency>
Deezpatch jars are published with Automatic-Module-Name manifest attribute:
- Core -
io.github.joeljeremy.deezpatch.core
Module authors can use above module names in their module-info.java:
modulefoo.bar {requiresio.github.joeljeremy.deezpatch.core;}
What differentiates Deezpatch from other messaging/dispatch libraries? The library takes advantage of the benefits provided byjava.lang.invoke.LambdaMetafactory to avoid the cost of invoking methods reflectively. This results in performance close to directly invoking the request handler and event handler methods!
Requests are messages that either:
publicclassGreetCommandimplementsRequest<Void> {privatefinalStringname;publicGreetRequest(Stringname) {this.name =name; }publicStringname() {returnname; }}publicclassPingQueryimplementsRequest<Pong> {}
Requests are handled by request handlers. Request handlers can be registered through the use of the@RequestHandler annotation.
A request must only have a single request handler.
(@RequestHandlers fully support methods withvoid return types! No need to set method return type toVoid and returnnull for no reason.)
publicclassGreetCommandHandler {@RequestHandlerpublicvoidhandle(GreetCommandcommand) {sayHi(command.name()); }}publicclassPingQueryHandler {@RequestHandlerpublicPonghandle(PingQueryquery) {returnnewPong("Here's your pong!"); }}
Requests are dispatched to a single request handler and this can be done through a dispatcher.
publicstaticvoidmain(String[]args) {// Use Spring's application context as InstanceProvider in this example// but any other DI framework can be used e.g. Guice, Dagger, etc.ApplicationContextapplicationContext =springApplicationContext();// Deezpatch implements the Dispatcher interface.Dispatcherdispatcher =Deezpatch.builder() .instanceProvider(applicationContext::getBean) .requests(config ->config.handlers(GreetCommandHandler.java,PingQueryHandler.java )) .build();// Send command!dispatcher.send(newGreetCommand("Deez"));// Send query!Optional<Pong>pong =dispatcher.send(newPingQuery());}
Events are messages that indicate that something has occurred in the system.
publicclassGreetedEventimplementsEvent {privatefinalStringgreeting;publicGreetedEvent(Stringgreeting) {this.greeting =greeting; }publicStringgreeting() {returngreeting; }}
Events are handled by event handlers. Event handlers can be registered through the use of the@EventHandler annotation.
An event can have zero or more event handlers.
publicclassGreetedEventHandler {@EventHandlerpublicvoidsayHello(GreetedEventevent) {// Well, hello! }@EventHandlerpublicvoidsayKumusta(GreetedEventevent) {// Well, kumusta? }@EventHandlerpublicvoidsayGotEm(GreetedEventevent) {// Got 'em! }}
Events are dispatched to zero or more event handlers and this can be done through a publisher.
publicstaticvoidmain(String[]args) {// Use Spring's application context as InstanceProvider in this example// but any other DI framework can be used e.g. Guice, Dagger, etc.ApplicationContextapplicationContext =springApplicationContext();// Deezpatch implements the Publisher interface.Publisherpublisher =Deezpatch.builder() .instanceProvider(applicationContext::getBean) .events(config ->config.handlers(GreetedEventHandler.java )) .build();// Publish event!publisher.publish(newGreetedEvent("Hi from Deez!"));}
The library provides anInstanceProvider interface as an extension point to let users customize how request/event handler instances should be instantiated. This can be as simple asnew-ing up request/event handlers or getting instances from a DI framework such as Spring'sApplicationContext, Guice'sInjector, etc.
// Application.javapublicstaticvoidmain(String[]args) {Deezpatchdeezpatch =Deezpatch.builder() .instanceProvider(Application::getInstance) .requests(...) .events(...) .build();}privatestaticObjectgetInstance(Class<?>handlerType) {if (MyRequestHandler.class.equals(handlerType)) {returnnewMyRequestHandler(); }elseif (MyEventHandler.class.equals(handlerType)) {returnnewMyEventHandler(); }thrownewIllegalStateException("Failed to get instance for " +handlerType.getName() +".");}
publicstaticvoidmain(String[]args) {ApplicationContextapplicationContext =springApplicationContext();Deezpatchdeezpatch =Deezpatch.builder() .instanceProvider(applicationContext::getBean) .requests(...) .events(...) .build();}
publicstaticvoidmain(String[]args) {Injectorinjector =guiceInjector();Deezpatchdeezpatch =Deezpatch.builder() .instanceProvider(injector::getInstance) .requests(...) .events(...) .build();}
In cases where a project is built in such a way that bringing in external dependencies is considered a bad practice (e.g. domain layer/package in a Hexagonal (Ports and Adapters) architecture), Deezpatch provides a way to use custom request/event handler annotations (in addition to the built-inRequestHandler andEventHandler annotations) to annotate request/event handlers.
This way, Deezpatch can still be used without adding the core Deezpatch library as a dependency of a project's domain layer/package. Instead, it may be used in the outer layers/packages to wire things up.
// Let's say below classes are declared in a project's core/domain package:@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)public @interfaceAwesomeRequestHandler {}@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)public @interfaceAwesomeEventHandler {}publicclassMyRequestHandler {@AwesomeRequestHandlerpublicvoidhandle(TestRequestrequest) {// Handle. }}publicclassMyEventHandler {@AwesomeEventHandlerpublicvoidhandle(TestEventevent) {// Handle. }}// To wire things up:publicstaticvoidmain(String[]args) {// Use Spring's application context as InstanceProvider in this example// but any other DI framework can be used e.g. Guice, Dagger, etc.ApplicationContextapplicationContext =springApplicationContext();// Register handlers and custom annotations.Deezpatchdeezpatch =Deezpatch.builder() .instanceProvider(applicationContext::getBean) .requests(config ->config.handlerAnnotations(AwesomeRequestHandler.class) .handlers(MyRequestHandler.class)) .events(config ->config.handlerAnnotations(AwesomeEventHandler.java) .handlers(MyEventHandler.class)) .build();}
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