Update README.md

axon/README.md

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+## Axon
+
+This module contains articles about Axon
+
+### Relevant articles
+
+- [A Guide to the Axon Framework](https://www.baeldung.com/axon-cqrs-event-sourcing)

axon/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>axon</artifactId>
+    <name>axon</name>
+    <description>Basic Axon Framework with Spring Boot configuration tutorial</description>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-boot-2</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-boot-2</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.axonframework</groupId>
+            <artifactId>axon-spring-boot-starter</artifactId>
+            <version>${axon.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.axonframework</groupId>
+            <artifactId>axon-test</artifactId>
+            <version>${axon.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-autoconfigure</artifactId>
+            <scope>compile</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <scope>runtime</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <axon.version>4.1.2</axon.version>
+    </properties>
+
+</project>

axon/src/main/java/com/baeldung/axon/OrderApplication.java

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+package com.baeldung.axon;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class OrderApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(OrderApplication.class, args);
+    }
+
+}

axon/src/main/java/com/baeldung/axon/commandmodel/OrderAggregate.java

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+package com.baeldung.axon.commandmodel;
+
+import static org.axonframework.modelling.command.AggregateLifecycle.apply;
+
+import org.axonframework.commandhandling.CommandHandler;
+import org.axonframework.eventsourcing.EventSourcingHandler;
+import org.axonframework.modelling.command.AggregateIdentifier;
+import org.axonframework.spring.stereotype.Aggregate;
+
+import com.baeldung.axon.coreapi.commands.ConfirmOrderCommand;
+import com.baeldung.axon.coreapi.commands.PlaceOrderCommand;
+import com.baeldung.axon.coreapi.commands.ShipOrderCommand;
+import com.baeldung.axon.coreapi.events.OrderConfirmedEvent;
+import com.baeldung.axon.coreapi.events.OrderPlacedEvent;
+import com.baeldung.axon.coreapi.events.OrderShippedEvent;
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
+
+@Aggregate
+public class OrderAggregate {
+
+    @AggregateIdentifier
+    private String orderId;
+    private boolean orderConfirmed;
+
+    @CommandHandler
+    public OrderAggregate(PlaceOrderCommand command) {
+        apply(new OrderPlacedEvent(command.getOrderId(), command.getProduct()));
+    }
+
+    @CommandHandler
+    public void handle(ConfirmOrderCommand command) {
+        apply(new OrderConfirmedEvent(orderId));
+    }
+
+    @CommandHandler
+    public void handle(ShipOrderCommand command) {
+        if (!orderConfirmed) {
+            throw new UnconfirmedOrderException();
+        }
+
+        apply(new OrderShippedEvent(orderId));
+    }
+
+    @EventSourcingHandler
+    public void on(OrderPlacedEvent event) {
+        this.orderId = event.getOrderId();
+        this.orderConfirmed = false;
+    }
+
+    @EventSourcingHandler
+    public void on(OrderConfirmedEvent event) {
+        this.orderConfirmed = true;
+    }
+
+    protected OrderAggregate() {
+        // Required by Axon to build a default Aggregate prior to Event Sourcing
+    }
+
+}

axon/src/main/java/com/baeldung/axon/coreapi/commands/ConfirmOrderCommand.java

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+package com.baeldung.axon.coreapi.commands;
+
+import org.axonframework.modelling.command.TargetAggregateIdentifier;
+
+import java.util.Objects;
+
+public class ConfirmOrderCommand {
+
+    @TargetAggregateIdentifier
+    private final String orderId;
+
+    public ConfirmOrderCommand(String orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final ConfirmOrderCommand other = (ConfirmOrderCommand) obj;
+        return Objects.equals(this.orderId, other.orderId);
+    }
+
+    @Override
+    public String toString() {
+        return "ConfirmOrderCommand{" +
+                "orderId='" + orderId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/commands/PlaceOrderCommand.java

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+package com.baeldung.axon.coreapi.commands;
+
+import java.util.Objects;
+
+import org.axonframework.modelling.command.TargetAggregateIdentifier;
+
+public class PlaceOrderCommand {
+
+    @TargetAggregateIdentifier
+    private final String orderId;
+    private final String product;
+
+    public PlaceOrderCommand(String orderId, String product) {
+        this.orderId = orderId;
+        this.product = product;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProduct() {
+        return product;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, product);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final PlaceOrderCommand other = (PlaceOrderCommand) obj;
+        return Objects.equals(this.orderId, other.orderId)
+                && Objects.equals(this.product, other.product);
+    }
+
+    @Override
+    public String toString() {
+        return "PlaceOrderCommand{" +
+                "orderId='" + orderId + '\'' +
+                ", product='" + product + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/commands/ShipOrderCommand.java

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+package com.baeldung.axon.coreapi.commands;
+
+import java.util.Objects;
+
+import org.axonframework.modelling.command.TargetAggregateIdentifier;
+
+public class ShipOrderCommand {
+
+    @TargetAggregateIdentifier
+    private final String orderId;
+
+    public ShipOrderCommand(String orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final ShipOrderCommand other = (ShipOrderCommand) obj;
+        return Objects.equals(this.orderId, other.orderId);
+    }
+
+    @Override
+    public String toString() {
+        return "ShipOrderCommand{" +
+                "orderId='" + orderId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/OrderConfirmedEvent.java

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+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class OrderConfirmedEvent {
+
+    private final String orderId;
+
+    public OrderConfirmedEvent(String orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final OrderConfirmedEvent other = (OrderConfirmedEvent) obj;
+        return Objects.equals(this.orderId, other.orderId);
+    }
+
+    @Override
+    public String toString() {
+        return "OrderConfirmedEvent{" +
+                "orderId='" + orderId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/OrderPlacedEvent.java

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+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class OrderPlacedEvent {
+
+    private final String orderId;
+    private final String product;
+
+    public OrderPlacedEvent(String orderId, String product) {
+        this.orderId = orderId;
+        this.product = product;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProduct() {
+        return product;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, product);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final OrderPlacedEvent other = (OrderPlacedEvent) obj;
+        return Objects.equals(this.orderId, other.orderId)
+                && Objects.equals(this.product, other.product);
+    }
+
+    @Override
+    public String toString() {
+        return "OrderPlacedEvent{" +
+                "orderId='" + orderId + '\'' +
+                ", product='" + product + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/OrderShippedEvent.java

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+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class OrderShippedEvent {
+
+    private final String orderId;
+
+    public OrderShippedEvent(String orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final OrderShippedEvent other = (OrderShippedEvent) obj;
+        return Objects.equals(this.orderId, other.orderId);
+    }
+
+    @Override
+    public String toString() {
+        return "OrderShippedEvent{" +
+                "orderId='" + orderId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/exceptions/UnconfirmedOrderException.java

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+package com.baeldung.axon.coreapi.exceptions;
+
+public class UnconfirmedOrderException extends IllegalStateException {
+
+    public UnconfirmedOrderException() {
+        super("Cannot ship an order which has not been confirmed yet.");
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/queries/FindAllOrderedProductsQuery.java

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+package com.baeldung.axon.coreapi.queries;
+
+public class FindAllOrderedProductsQuery {
+
+}

axon/src/main/java/com/baeldung/axon/coreapi/queries/OrderStatus.java

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+package com.baeldung.axon.coreapi.queries;
+
+public enum OrderStatus {
+
+    PLACED, CONFIRMED, SHIPPED
+
+}

axon/src/main/java/com/baeldung/axon/coreapi/queries/OrderedProduct.java

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+package com.baeldung.axon.coreapi.queries;
+
+import java.util.Objects;
+
+public class OrderedProduct {
+
+    private final String orderId;
+    private final String product;
+    private OrderStatus orderStatus;
+
+    public OrderedProduct(String orderId, String product) {
+        this.orderId = orderId;
+        this.product = product;
+        orderStatus = OrderStatus.PLACED;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProduct() {
+        return product;
+    }
+
+    public OrderStatus getOrderStatus() {
+        return orderStatus;
+    }
+
+    public void setOrderConfirmed() {
+        this.orderStatus = OrderStatus.CONFIRMED;
+    }
+
+    public void setOrderShipped() {
+        this.orderStatus = OrderStatus.SHIPPED;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, product, orderStatus);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        final OrderedProduct other = (OrderedProduct) obj;
+        return Objects.equals(this.orderId, other.orderId)
+                && Objects.equals(this.product, other.product)
+                && Objects.equals(this.orderStatus, other.orderStatus);
+    }
+
+    @Override
+    public String toString() {
+        return "OrderedProduct{" +
+                "orderId='" + orderId + '\'' +
+                ", product='" + product + '\'' +
+                ", orderStatus=" + orderStatus +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/gui/OrderRestEndpoint.java

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+package com.baeldung.axon.gui;
+
+import java.util.List;
+import java.util.UUID;
+
+import org.axonframework.commandhandling.gateway.CommandGateway;
+import org.axonframework.messaging.responsetypes.ResponseTypes;
+import org.axonframework.queryhandling.QueryGateway;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import com.baeldung.axon.coreapi.commands.ConfirmOrderCommand;
+import com.baeldung.axon.coreapi.commands.PlaceOrderCommand;
+import com.baeldung.axon.coreapi.commands.ShipOrderCommand;
+import com.baeldung.axon.coreapi.queries.FindAllOrderedProductsQuery;
+import com.baeldung.axon.coreapi.queries.OrderedProduct;
+
+@RestController
+public class OrderRestEndpoint {
+
+    private final CommandGateway commandGateway;
+    private final QueryGateway queryGateway;
+
+    public OrderRestEndpoint(CommandGateway commandGateway, QueryGateway queryGateway) {
+        this.commandGateway = commandGateway;
+        this.queryGateway = queryGateway;
+    }
+
+    @PostMapping("/ship-order")
+    public void shipOrder() {
+        String orderId = UUID.randomUUID().toString();
+        commandGateway.send(new PlaceOrderCommand(orderId, "Deluxe Chair"));
+        commandGateway.send(new ConfirmOrderCommand(orderId));
+        commandGateway.send(new ShipOrderCommand(orderId));
+    }
+
+    @PostMapping("/ship-unconfirmed-order")
+    public void shipUnconfirmedOrder() {
+        String orderId = UUID.randomUUID().toString();
+        commandGateway.send(new PlaceOrderCommand(orderId, "Deluxe Chair"));
+        // This throws an exception, as an Order cannot be shipped if it has not been confirmed yet.
+        commandGateway.send(new ShipOrderCommand(orderId));
+    }
+
+    @GetMapping("/all-orders")
+    public List<OrderedProduct> findAllOrderedProducts() {
+        return queryGateway.query(new FindAllOrderedProductsQuery(), ResponseTypes.multipleInstancesOf(OrderedProduct.class))
+                           .join();
+    }
+
+}

axon/src/main/java/com/baeldung/axon/querymodel/OrderedProductsEventHandler.java

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+package com.baeldung.axon.querymodel;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.axonframework.config.ProcessingGroup;
+import org.axonframework.eventhandling.EventHandler;
+import org.axonframework.queryhandling.QueryHandler;
+import org.springframework.stereotype.Service;
+
+import com.baeldung.axon.coreapi.events.OrderConfirmedEvent;
+import com.baeldung.axon.coreapi.events.OrderPlacedEvent;
+import com.baeldung.axon.coreapi.events.OrderShippedEvent;
+import com.baeldung.axon.coreapi.queries.FindAllOrderedProductsQuery;
+import com.baeldung.axon.coreapi.queries.OrderedProduct;
+
+@Service
+@ProcessingGroup("ordered-products")
+public class OrderedProductsEventHandler {
+
+    private final Map<String, OrderedProduct> orderedProducts = new HashMap<>();
+
+    @EventHandler
+    public void on(OrderPlacedEvent event) {
+        String orderId = event.getOrderId();
+        orderedProducts.put(orderId, new OrderedProduct(orderId, event.getProduct()));
+    }
+
+    @EventHandler
+    public void on(OrderConfirmedEvent event) {
+        orderedProducts.computeIfPresent(event.getOrderId(), (orderId, orderedProduct) -> {
+            orderedProduct.setOrderConfirmed();
+            return orderedProduct;
+        });
+    }
+
+    @EventHandler
+    public void on(OrderShippedEvent event) {
+        orderedProducts.computeIfPresent(event.getOrderId(), (orderId, orderedProduct) -> {
+            orderedProduct.setOrderShipped();
+            return orderedProduct;
+        });
+    }
+
+    @QueryHandler
+    public List<OrderedProduct> handle(FindAllOrderedProductsQuery query) {
+        return new ArrayList<>(orderedProducts.values());
+    }
+
+}

axon/src/main/resources/application.properties

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+spring.application.name=Order Management Service

axon/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

axon/src/main/resources/order-api.http

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+POST http://localhost:8080/ship-order
+
+###
+
+POST http://localhost:8080/ship-unconfirmed-order
+
+###
+
+GET http://localhost:8080/all-orders
+
+###

axon/src/test/java/com/baeldung/axon/commandmodel/OrderAggregateUnitTest.java

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+package com.baeldung.axon.commandmodel;
+
+import java.util.UUID;
+
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
+import org.axonframework.test.aggregate.AggregateTestFixture;
+import org.axonframework.test.aggregate.FixtureConfiguration;
+import org.junit.*;
+
+import com.baeldung.axon.coreapi.commands.ConfirmOrderCommand;
+import com.baeldung.axon.coreapi.commands.PlaceOrderCommand;
+import com.baeldung.axon.coreapi.commands.ShipOrderCommand;
+import com.baeldung.axon.coreapi.events.OrderConfirmedEvent;
+import com.baeldung.axon.coreapi.events.OrderPlacedEvent;
+import com.baeldung.axon.coreapi.events.OrderShippedEvent;
+
+public class OrderAggregateUnitTest {
+
+    private FixtureConfiguration<OrderAggregate> fixture;
+
+    @Before
+    public void setUp() {
+        fixture = new AggregateTestFixture<>(OrderAggregate.class);
+    }
+
+    @Test
+    public void giveNoPriorActivity_whenPlaceOrderCommand_thenShouldPublishOrderPlacedEvent() {
+        String orderId = UUID.randomUUID().toString();
+        String product = "Deluxe Chair";
+        fixture.givenNoPriorActivity()
+               .when(new PlaceOrderCommand(orderId, product))
+               .expectEvents(new OrderPlacedEvent(orderId, product));
+    }
+
+    @Test
+    public void givenOrderPlacedEvent_whenConfirmOrderCommand_thenShouldPublishOrderConfirmedEvent() {
+        String orderId = UUID.randomUUID().toString();
+        String product = "Deluxe Chair";
+        fixture.given(new OrderPlacedEvent(orderId, product))
+               .when(new ConfirmOrderCommand(orderId))
+               .expectEvents(new OrderConfirmedEvent(orderId));
+    }
+
+    @Test
+    public void givenOrderPlacedEvent_whenShipOrderCommand_thenShouldThrowUnconfirmedOrderException() {
+        String orderId = UUID.randomUUID().toString();
+        String product = "Deluxe Chair";
+        fixture.given(new OrderPlacedEvent(orderId, product))
+               .when(new ShipOrderCommand(orderId))
+               .expectException(UnconfirmedOrderException.class);
+    }
+
+    @Test
+    public void givenOrderPlacedEventAndOrderConfirmedEvent_whenShipOrderCommand_thenShouldPublishOrderShippedEvent() {
+        String orderId = UUID.randomUUID().toString();
+        String product = "Deluxe Chair";
+        fixture.given(new OrderPlacedEvent(orderId, product), new OrderConfirmedEvent(orderId))
+               .when(new ShipOrderCommand(orderId))
+               .expectEvents(new OrderShippedEvent(orderId));
+    }
+
+}