Add servlet code

web-modules/jakarta-servlets/Storing_Java_Objects/pom.xml

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+<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>
+    <groupId>com.example</groupId>
+    <artifactId>session-demo</artifactId>
+    <version>1.0</version>
+    <packaging>war</packaging>
+
+    <dependencies>
+        <!-- Servlet API -->
+        <dependency>
+            <groupId>jakarta.servlet</groupId>
+            <artifactId>jakarta.servlet-api</artifactId>
+            <version>6.0.0</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- SLF4J + Logback for logging -->
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>1.4.11</version>
+        </dependency>
+
+        <!-- JUnit 5 for writing tests -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.0</version>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- Mockito for mocking servlet objects -->
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>5.5.0</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <finalName>session-demo</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.11.0</version>
+                <configuration>
+                    <source>21</source>
+                    <target>21</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

web-modules/jakarta-servlets/Storing_Java_Objects/src/main/java/com/example/RemoveSessionServlet.java

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+package com.example;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import jakarta.servlet.*;
+import jakarta.servlet.http.*;
+import jakarta.servlet.annotation.WebServlet;
+import java.io.*;
+
+@WebServlet("/remove-session")
+public class RemoveSessionServlet extends HttpServlet {
+
+    private static final Logger logger = LoggerFactory.getLogger(RemoveSessionServlet.class);
+
+    protected void doPost(HttpServletRequest request, HttpServletResponse response)
+            throws ServletException, IOException {
+
+        // Get the existing session without creating a new one
+        HttpSession session = request.getSession(false);
+
+        if (session != null) {
+            String sessionId = session.getId();
+
+            // Remove only a specific attribute
+            session.removeAttribute("loggedInUser");
+            logger.info("User attribute removed from session ID: {}", sessionId);
+
+            // Invalidate the entire session (e.g., on logout)
+            session.invalidate();
+            logger.info("Session '{}' has been invalidated.", sessionId);
+
+        } else {
+            logger.warn("No active session found to remove.");
+        }
+    }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/main/java/com/example/RetrieveSessionServlet.java

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+package com.example;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import jakarta.servlet.*;
+import jakarta.servlet.http.*;
+import jakarta.servlet.annotation.WebServlet;
+import java.io.*;
+
+@WebServlet("/retrieve-session")
+public class RetrieveSessionServlet extends HttpServlet {
+
+    private static final Logger logger = LoggerFactory.getLogger(RetrieveSessionServlet.class);
+
+    protected void doGet(HttpServletRequest request, HttpServletResponse response)
+            throws ServletException, IOException {
+
+        // Get the existing session without creating a new one
+        HttpSession session = request.getSession(false);
+
+        if (session != null) {
+            // Retrieve the User object from the session
+            User user = (User) session.getAttribute("loggedInUser");
+
+            if (user != null) {
+                logger.info("Retrieved user: {}, Email: {}", 
+                    user.getUsername(), user.getEmail());
+            } else {
+                logger.warn("No user found in session.");
+            }
+        } else {
+            logger.warn("No active session found.");
+        }
+    }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/main/java/com/example/StoreSessionServlet.java

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+package com.example;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import jakarta.servlet.*;
+import jakarta.servlet.http.*;
+import jakarta.servlet.annotation.WebServlet;
+import java.io.*;
+
+@WebServlet("/store-session")
+public class StoreSessionServlet extends HttpServlet {
+
+    private static final Logger logger = LoggerFactory.getLogger(StoreSessionServlet.class);
+
+    protected void doPost(HttpServletRequest request, HttpServletResponse response)
+            throws ServletException, IOException {
+
+        // Create a User object
+        User user = new User("john_doe", "john@example.com");
+
+        // Get or create the session
+        HttpSession session = request.getSession();
+
+        // Store the User object in the session
+        session.setAttribute("loggedInUser", user);
+
+        logger.info("User '{}' stored in session with ID: {}", 
+            user.getUsername(), session.getId());
+    }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/main/java/com/example/User.java

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+package com.example;
+
+import java.io.Serializable;
+
+public class User implements Serializable {
+    private static final long serialVersionUID = 1L;
+    private String username;
+    private String email;
+
+    public User(String username, String email) {
+        this.username = username;
+        this.email = email;
+    }
+
+    public String getUsername() { return username; }
+    public String getEmail() { return email; }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/main/webapp/WEB-INF/web.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee 
+         https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd"
+         version="6.0">
+</web-app>

web-modules/jakarta-servlets/Storing_Java_Objects/src/test/java/com/example/RemoveSessionServletUnitTest.java

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+package com.example;
+
+import jakarta.servlet.http.*;
+import org.junit.jupiter.api.Test;
+import static org.mockito.Mockito.*;
+
+public class RemoveSessionServletTest {
+
+    @Test
+    void testUserRemovedFromSession() throws Exception {
+
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+        HttpSession session = mock(HttpSession.class);
+
+        when(request.getSession(false)).thenReturn(session);
+        when(session.getId()).thenReturn("TEST-SESSION-ID");
+
+        // Run the servlet
+        RemoveSessionServlet servlet = new RemoveSessionServlet();
+        servlet.doPost(request, response);
+
+        // Verify removeAttribute and invalidate were both called
+        verify(session).removeAttribute("loggedInUser");
+        verify(session).invalidate();
+    }
+
+    @Test
+    void testNoSessionToRemove() throws Exception {
+
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+
+        // Simulate no active session
+        when(request.getSession(false)).thenReturn(null);
+
+        // Run the servlet — should handle null gracefully
+        RemoveSessionServlet servlet = new RemoveSessionServlet();
+        servlet.doPost(request, response);
+
+        // No exception should be thrown
+    }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/test/java/com/example/RetrieveSessionServletUnitTest.java

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+package com.example;
+
+import jakarta.servlet.http.*;
+import org.junit.jupiter.api.Test;
+import static org.mockito.Mockito.*;
+
+public class RetrieveSessionServletTest {
+
+    @Test
+    void testUserRetrievedFromSession() throws Exception {
+
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+        HttpSession session = mock(HttpSession.class);
+        User mockUser = new User("john_doe", "john@example.com");
+
+        // Return our mock session and user
+        when(request.getSession(false)).thenReturn(session);
+        when(session.getAttribute("loggedInUser")).thenReturn(mockUser);
+
+        // Run the servlet
+        RetrieveSessionServlet servlet = new RetrieveSessionServlet();
+        servlet.doGet(request, response);
+
+        // Verify getAttribute was called with the correct key
+        verify(session).getAttribute("loggedInUser");
+    }
+
+    @Test
+    void testNoSessionFound() throws Exception {
+
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+
+        // Simulate no active session
+        when(request.getSession(false)).thenReturn(null);
+
+        // Run the servlet — should handle null gracefully
+        RetrieveSessionServlet servlet = new RetrieveSessionServlet();
+        servlet.doGet(request, response);
+
+        // No exception should be thrown
+    }
+}

web-modules/jakarta-servlets/Storing_Java_Objects/src/test/java/com/example/StoreSessionServletUnitTest.java

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+package com.example;
+
+import jakarta.servlet.http.*;
+import org.junit.jupiter.api.Test;
+import static org.mockito.Mockito.*;
+
+public class StoreSessionServletTest {
+
+    @Test
+    void testUserStoredInSession() throws Exception {
+
+        // Mock the request, response, and session
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+        HttpSession session = mock(HttpSession.class);
+
+        // When getSession() is called, return our mock session
+        when(request.getSession()).thenReturn(session);
+
+        // Run the servlet
+        StoreSessionServlet servlet = new StoreSessionServlet();
+        servlet.doPost(request, response);
+
+        // Verify setAttribute was called with a User object
+        verify(session).setAttribute(eq("loggedInUser"), any(User.class));
+    }
+}