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/README.md

@@ -0,0 +1,184 @@
+---
+title: Context object
+category: Creational
+language: en
+tags:
+- Data access
+---
+
+## Name / classification
+
+Context Object
+
+## Also known as
+
+Context, Encapsulate Context
+
+## Intent
+
+Decouple data from protocol-specific classes and store the scoped data in an object independent 
+of the underlying protocol technology. 
+
+## Explanation
+
+Real-world example
+
+> This application has different layers labelled A, B and C with each extracting specific information
+> from a similar context for further use in the software. Passing down each pieces of information 
+> individually would be inefficient, a method to efficiently store and pass information is needed.  
+
+In plain words
+
+> Create an object and store the data there and pass this object to where it is needed.
+
+[Core J2EE Patterns](http://corej2eepatterns.com/ContextObject.htm) says
+
+> Use a Context Object to encapsulate state in a protocol-independent way to be shared throughout your application. 
+
+**Programmatic Example**
+
+We define what data a service context object contains.
+
+```Java
+public class ServiceContext {
+
+    String ACCOUNT_SERVICE, SESSION_SERVICE, SEARCH_SERVICE;
+
+    public void setACCOUNT_SERVICE(String ACCOUNT_SERVICE) {
+        this.ACCOUNT_SERVICE = ACCOUNT_SERVICE;
+    }
+
+    public void setSESSION_SERVICE(String SESSION_SERVICE) {
+        this.SESSION_SERVICE = SESSION_SERVICE;
+    }
+
+    public void setSEARCH_SERVICE(String SEARCH_SERVICE) {
+        this.SEARCH_SERVICE = SEARCH_SERVICE;
+    }
+
+    public String getACCOUNT_SERVICE() {
+        return ACCOUNT_SERVICE;
+    }
+
+    public String getSESSION_SERVICE() {
+        return SESSION_SERVICE;
+    }
+
+    public String getSEARCH_SERVICE() {
+        return SEARCH_SERVICE;
+    }
+    
+    public String toString() { return ACCOUNT_SERVICE + " " + SESSION_SERVICE + " " + SEARCH_SERVICE;}
+}
+```
+
+Create an interface used in parts of the application for context objects to be created.
+
+```Java
+public class ServiceContextFactory {
+
+    public static ServiceContext createContext() {
+        return new ServiceContext();
+    }
+}
+```
+
+Instantiate the context object in the first layer and the adjoining layer upcalls the context in the current layer, which
+then further structures the object.
+
+```Java
+public class LayerA {
+
+    private static ServiceContext context;
+
+    public LayerA() {
+        context = ServiceContextFactory.createContext();
+    }
+
+    public static ServiceContext getContext() {
+        return context;
+    }
+
+    public void addAccountInfo(String accountService) {
+        context.setACCOUNT_SERVICE(accountService);
+    }
+}
+
+public class LayerB {
+
+    private static ServiceContext context;
+
+    public LayerB(LayerA layerA) {
+        this.context = layerA.getContext();
+    }
+
+    public static ServiceContext getContext() {
+        return context;
+    }
+
+    public void addSessionInfo(String sessionService) {
+        context.setSESSION_SERVICE(sessionService);
+    }
+}
+
+public class LayerC {
+
+    public static ServiceContext context;
+
+    public LayerC(LayerB layerB) {
+        this.context = layerB.getContext();
+    }
+
+    public static ServiceContext getContext() {
+        return context;
+    }
+
+    public void addSearchInfo(String searchService) {
+        context.setSEARCH_SERVICE(searchService);
+    }
+}
+```
+Here is the context object and layers in action.
+
+```Java
+var layerA = new LayerA();
+layerA.addAccountInfo(SERVICE);
+LOGGER.info("Context = {}",layerA.getContext());
+var layerB = new LayerB(layerA);
+layerB.addSessionInfo(SERVICE);
+LOGGER.info("Context = {}",layerB.getContext());
+var layerC = new LayerC(layerB);
+layerC.addSearchInfo(SERVICE);
+LOGGER.info("Context = {}",layerC.getContext());
+```
+
+Program output:
+
+```Java
+Context = SERVICE null null
+Context = SERVICE SERVICE null
+Context = SERVICE SERVICE SERVICE
+```
+
+## Class diagram
+
+![alt text](./etc/context-object.png "Context object")
+
+## Application
+
+Use the Context Object pattern for:
+
+* Sharing information across different system layers.
+* Decoupling software data from protocol-specific contexts.
+* Exposing only the relevant API's within the context.
+
+## Known uses
+* [Spring: ApplicationContext](https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/ApplicationContext.html)
+* [Oracle: SecurityContext](https://docs.oracle.com/javaee/7/api/javax/ws/rs/core/SecurityContext.html)
+* [Oracle: ServletContext](https://docs.oracle.com/javaee/6/api/javax/servlet/ServletContext.html)
+
+## Credits
+
+* [J2EE Design Patterns](http://corej2eepatterns.com/ContextObject.htm)
+* [Allan Kelly - The Encapsulate Context Pattern](https://accu.org/journals/overload/12/63/kelly_246/)
+* [Arvid S. Krishna et al. - Context Object](https://www.dre.vanderbilt.edu/~schmidt/PDF/Context-Object-Pattern.pdf)