feature: #1288 Added The Client Session Design Pattern (#2155)

* #1288 Add client session design pattern

* #1288 Add license to files

* Inserted README file for session_state_pattern

* Added real-world example to client-session/README

* #1288 Add server tests

* #1288 Fixed code smells

* #1288 Removed unused getter and setters

* #1288 incorporated feedback

* #1288 Added maven-assembly-plugin

* #1288 Added more description

Co-authored-by: Nakul Nambiar <u7433687@anu.edu.au>
Co-authored-by: Denis <u7281557@anu.edu.au>

client-session/README.md

@@ -0,0 +1,114 @@
+---
+title: Client Session Pattern
+category: Architectural
+language: en
+tags:
+- Decoupling
+---
+
+## Name
+
+[Client Session pattern](https://dzone.com/articles/practical-php-patterns/practical-php-patterns-client)
+
+## Intent
+
+- Create stateless servers that removes the problem of clustering, as users can switch between servers seamlessly.
+- Makes data more resilient in case of server fail-over.
+- Works well with smaller data sizes.
+
+## Explanation
+
+Real-World Example
+
+> You're looking to create a data management app allowing users to send requests to the server to 
+> modify and make changes to data stored on their devices. These requests are small in size and the 
+> data is individual to each user, negating the need for a large scale database implementation. 
+> Using the client session pattern, you are able to handle multiple concurrent requests, load 
+> balancing clients across different servers with ease due to servers remaining stateless. You also 
+> remove the need to store session IDs on the server side due to clients providing all the 
+> information that a server needs to perform their process.
+
+In Plain words
+
+> Instead of storing information about the current client and the information being accessed on the 
+> server, it is maintained client side only. Client has to send session data with each request to 
+> the server and has to send an updated state back to the client, which is stored on the clients 
+> machine. The server doesn't have to store the client information.
+> ([ref](https://dzone.com/articles/practical-php-patterns/practical-php-patterns-client))
+
+**Programmatic Example**
+
+Here is the sample code to describe the client-session pattern. In the below code we are first 
+creating an instance of the Server. This server instance will then be used to get Session objects 
+for two clients. As you can see from the code below the Session object can be used to store any 
+relevant information that are required by the server to process the client request. These session 
+objects will then be passed on with every Request to the server. The Request will have the Session 
+object that stores the relevant client details along with the required data for processing the 
+request. The session information in every request helps the server identify the client and process 
+the request accordingly. 
+
+```java
+public class App {
+
+  public static void main(String[] args) {
+    var server = new Server("localhost", 8080);
+    var session1 = server.getSession("Session1");
+    var session2 = server.getSession("Session2");
+    var request1 = new Request("Data1", session1);
+    var request2 = new Request("Data2", session2);
+    server.process(request1);
+    server.process(request2);
+  }
+}
+
+@Data
+@AllArgsConstructor
+public class Session {
+
+  /**
+   * Session id.
+   */
+  private String id;
+
+  /**
+   * Client name.
+   */
+  private String clientName;
+
+}
+
+@Data
+@AllArgsConstructor
+public class Request {
+
+  private String data;
+
+  private Session session;
+
+}
+```
+
+## Architecture Diagram
+
+![alt text](./etc/session_state_pattern.png "Session State Pattern")
+
+## Applicability
+
+Use the client state pattern when:
+
+- Processing smaller amounts of data to prevent larger requests and response sizes.
+- Remove the need for servers to save client states. Doing so also removes the need to store session IDs.
+- Clustering is an issue and needs to be avoided. Stateless servers allow clients to be easily distributed across servers.
+- Creates resilience from data losses due to server fails.
+
+## Consequences
+
+- The server is stateless. Any compute API will not store any data.
+- Struggles to deal with large amounts of data. Creates longer send and receive times due to larger amounts of session data to manage.
+- Security. All data is stored on the client's machine. This means that any vulnerabilities on the clients side can expose all data being sent and received by the server.
+
+
+## Credits
+
+- [Dzone - Practical PHP patterns](https://dzone.com/articles/practical-php-patterns/practical-php-patterns-client)
+- [Client Session State Design Pattern - Ram N Java](https://www.youtube.com/watch?v=ycOSj9g41pc)

client-session/pom.xml

@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+
+    The MIT License
+    Copyright © 2014-2022 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<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>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.26.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>client-session</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.client.session.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

client-session/src/main/java/com/iluwatar/client/session/App.java

@@ -0,0 +1,55 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.client.session;
+
+/**
+ * The Client-Session pattern allows the session data to be stored on the client side and send this
+ * data to the server with each request.
+ *
+ * <p> In this example, The {@link Server} class represents the server that would process the
+ * incoming {@link Request} and also assign {@link Session} to a client. Here one instance of Server
+ * is created. The we create two sessions for two different clients. These sessions are then passed
+ * on to the server in the request along with the data. The server is then able to interpret the
+ * client based on the session associated with it.
+ * </p>
+ */
+public class App {
+
+  /**
+   * Program entry point.
+   *
+   * @param args Command line args
+   */
+  public static void main(String[] args) {
+    var server = new Server("localhost", 8080);
+    var session1 = server.getSession("Session1");
+    var session2 = server.getSession("Session2");
+    var request1 = new Request("Data1", session1);
+    var request2 = new Request("Data2", session2);
+    server.process(request1);
+    server.process(request2);
+  }
+}

client-session/src/main/java/com/iluwatar/client/session/Request.java

@@ -0,0 +1,42 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.client.session;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+/**
+ * The Request class which contains the Session details and data.
+ */
+@Data
+@AllArgsConstructor
+public class Request {
+
+  private String data;
+
+  private Session session;
+
+}

client-session/src/main/java/com/iluwatar/client/session/Server.java

@@ -0,0 +1,65 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.client.session;
+
+import java.util.UUID;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * The Server class. The client communicates with the server and request processing and getting a new session.
+ */
+@Slf4j
+@Data
+@AllArgsConstructor
+public class Server {
+  private String host;
+
+  private int port;
+
+
+  /**
+   * Creates a new session.
+   *
+   * @param name name of the client
+   *
+   * @return Session Object
+   */
+  public Session getSession(String name) {
+    return new Session(UUID.randomUUID().toString(), name);
+  }
+
+  /**
+   * Processes a request based on the session.
+   *
+   * @param request Request object with data and Session
+   */
+  public void process(Request request) {
+    LOGGER.info("Processing Request with client: " + request.getSession().getClientName() + " data: " + request.getData());
+  }
+
+}

client-session/src/main/java/com/iluwatar/client/session/Session.java

@@ -0,0 +1,48 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.client.session;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+/**
+ * The Session class. Each client get assigned a Session which is then used for further communications.
+ */
+@Data
+@AllArgsConstructor
+public class Session {
+
+  /**
+   * Session id.
+   */
+  private String id;
+
+  /**
+   * Client name.
+   */
+  private String clientName;
+
+}

client-session/src/test/java/com/iluwatar/client/session/AppTest.java

@@ -0,0 +1,38 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.client.session;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+class AppTest {
+
+  @Test
+  void appStartsWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}

client-session/src/test/java/com/iluwatar/client/session/ServerTest.java

@@ -0,0 +1,14 @@
+package com.iluwatar.client.session;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class ServerTest {
+
+  @Test
+  void checkGetSession() {
+    Server server = new Server("localhost", 8080);
+    Session session = server.getSession("Session");
+    assertEquals("Session", session.getClientName());
+  }
+}

pom.xml

@@ -198,6 +198,7 @@
     <module>composite-view</module>
     <module>metadata-mapping</module>
     <module>service-to-worker</module>
+    <module>client-session</module>
     <module>embedded-value</module>
     <module>currying</module>
     <module>serialized-entity</module>