feature: Add context object pattern (#2304)

* Add context object pattern and corresponding tests

* Update context pattern

* Add README, class diagram, puml file.
Add toString method in ServiceContext.java.
Add tests for coverage.

* Improvements:
Remove plugin in pom file
Add comments in app.java
Change local variable keyword to var in app.java
Use lombok for getters, setters and tostring
Change method signature in context object

* Refreshing environment-1

* Reconfigure pom file.

Co-authored-by: Alvis Chan <u7287079@edu.anu.au>
Co-authored-by: u7287079 <u7287079@anu.edu.au>

context-object/src/main/java/com/iluwatar/context/object/App.java

@@ -0,0 +1,41 @@
+package com.iluwatar.context.object;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * In the context object pattern, information and data from underlying protocol-specific classes/systems is decoupled
+ * and stored into a protocol-independent object in an organised format. The pattern ensures the data contained within
+ * the context object can be shared and further structured between different layers of a software system.
+ *
+ * <p> In this example we show how a context object {@link ServiceContext} can be initiated, edited and passed/retrieved
+ * in different layers of the program ({@link LayerA}, {@link LayerB}, {@link LayerC}) through use of static methods. </p>
+ */
+@Slf4j
+public class App {
+
+    private static final String SERVICE = "SERVICE";
+
+    /**
+     * Program entry point.
+     * @param args command line args
+     */
+    public static void main(String[] args) {
+        //Initiate first layer and add service information into context
+        var layerA = new LayerA();
+        layerA.addAccountInfo(SERVICE);
+
+        LOGGER.info("Context = {}",layerA.getContext());
+
+        //Initiate second layer and preserving information retrieved in first layer through passing context object
+        var layerB = new LayerB(layerA);
+        layerB.addSessionInfo(SERVICE);
+
+        LOGGER.info("Context = {}",layerB.getContext());
+
+        //Initiate third layer and preserving information retrieved in first and second layer through passing context object
+        var layerC = new LayerC(layerB);
+        layerC.addSearchInfo(SERVICE);
+
+        LOGGER.info("Context = {}",layerC.getContext());
+    }
+}

context-object/src/main/java/com/iluwatar/context/object/LayerA.java

@@ -0,0 +1,17 @@
+package com.iluwatar.context.object;
+
+import lombok.Getter;
+
+@Getter
+public class LayerA {
+
+    private ServiceContext context;
+
+    public LayerA() {
+        context = ServiceContextFactory.createContext();
+    }
+
+    public void addAccountInfo(String accountService) {
+        context.setAccountService(accountService);
+    }
+}

context-object/src/main/java/com/iluwatar/context/object/LayerB.java

@@ -0,0 +1,17 @@
+package com.iluwatar.context.object;
+
+import lombok.Getter;
+
+@Getter
+public class LayerB {
+
+    private ServiceContext context;
+
+    public LayerB(LayerA layerA) {
+        this.context = layerA.getContext();
+    }
+
+    public void addSessionInfo(String sessionService) {
+        context.setSessionService(sessionService);
+    }
+}

context-object/src/main/java/com/iluwatar/context/object/LayerC.java

@@ -0,0 +1,17 @@
+package com.iluwatar.context.object;
+
+import lombok.Getter;
+
+@Getter
+public class LayerC {
+
+    public ServiceContext context;
+
+    public LayerC(LayerB layerB) {
+        this.context = layerB.getContext();
+    }
+
+    public void addSearchInfo(String searchService) {
+        context.setSearchService(searchService);
+    }
+}

context-object/src/main/java/com/iluwatar/context/object/ServiceContext.java

@@ -0,0 +1,16 @@
+package com.iluwatar.context.object;
+
+import lombok.Getter;
+import lombok.Setter;
+import lombok.ToString;
+
+/**
+ * Where context objects are defined.
+ */
+@ToString
+@Getter
+@Setter
+public class ServiceContext {
+
+   String AccountService, SessionService, SearchService;
+}

context-object/src/main/java/com/iluwatar/context/object/ServiceContextFactory.java

@@ -0,0 +1,11 @@
+package com.iluwatar.context.object;
+
+/**
+ * An interface to create context objects passed through layers.
+ */
+public class ServiceContextFactory {
+
+    public static ServiceContext createContext() {
+        return new ServiceContext();
+    }
+}

context-object/src/test/java/com/iluwatar/contect/object/AppTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.contect.object;
+
+import com.iluwatar.context.object.App;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+public class AppTest {
+
+    /**
+     * Test example app runs without error.
+     */
+    @Test
+    void shouldExecuteWithoutException() {
+        assertDoesNotThrow(() -> App.main(new String[]{}));
+    }
+}

context-object/src/test/java/com/iluwatar/contect/object/ServiceContextTest.java

@@ -0,0 +1,66 @@
+package com.iluwatar.contect.object;
+
+import com.iluwatar.context.object.LayerA;
+import com.iluwatar.context.object.LayerB;
+import com.iluwatar.context.object.LayerC;
+import com.iluwatar.context.object.ServiceContext;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+/**
+ * Date: 10/24/2022 - 3:18
+ *
+ * @author Chak Chan
+ */
+public class ServiceContextTest {
+
+    private static final String SERVICE = "SERVICE";
+
+    private LayerA layerA;
+
+    @BeforeEach
+    void initiateLayerA() {
+        this.layerA = new LayerA();
+    }
+
+    @Test
+    void testSameContextPassedBetweenLayers() {
+        ServiceContext context1 = layerA.getContext();
+        var layerB = new LayerB(layerA);
+        ServiceContext context2 = layerB.getContext();
+        var layerC = new LayerC(layerB);
+        ServiceContext context3 = layerC.getContext();
+
+        assertSame(context1, context2);
+        assertSame(context2, context3);
+        assertSame(context3, context1);
+    }
+
+    @Test
+    void testScopedDataPassedBetweenLayers() {
+        layerA.addAccountInfo(SERVICE);
+        var layerB = new LayerB(layerA);
+        var layerC = new LayerC(layerB);
+        layerC.addSearchInfo(SERVICE);
+        ServiceContext context = layerC.getContext();
+
+        assertEquals(SERVICE,context.getAccountService());
+        assertNull(context.getSessionService());
+        assertEquals(SERVICE,context.getSearchService());
+    }
+
+    @Test
+    void testToString() {
+        assertEquals(layerA.getContext().toString(),"ServiceContext(AccountService=null, SessionService=null, SearchService=null)");
+        layerA.addAccountInfo(SERVICE);
+        assertEquals(layerA.getContext().toString(), "ServiceContext(AccountService=SERVICE, SessionService=null, SearchService=null)");
+        var layerB = new LayerB(layerA);
+        layerB.addSessionInfo(SERVICE);
+        var layerC = new LayerC(layerB);
+        assertEquals(layerC.getContext().toString(), "ServiceContext(AccountService=SERVICE, SessionService=SERVICE, SearchService=null)");
+    }
+}