[BAEL-9099] Different Ways to Get Servlet Context

web-modules/jakarta-servlets-2/pom.xml

@@ -55,6 +55,26 @@
                 </exclusion>
             </exclusions>
         </dependency>
+
+        <dependency>
+            <groupId>org.eclipse.jetty</groupId>
+            <artifactId>jetty-server</artifactId>
+            <version>${jetty.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.jetty</groupId>
+            <artifactId>jetty-servlet</artifactId>
+            <version>${jetty.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.jetty</groupId>
+            <artifactId>jetty-client</artifactId>
+            <version>${jetty.version}</version>
+            <scope>test</scope>
+        </dependency>
+
     </dependencies>
 
     <build>
@@ -79,6 +99,7 @@
         <jakarta.servlet-api.version>6.1.0</jakarta.servlet-api.version>
         <jakarta.servlet.jsp-api.version>4.0.0</jakarta.servlet.jsp-api.version>
         <jakarta.servlet.jsp.jstl-api.version>3.0.0</jakarta.servlet.jsp.jstl-api.version>
+        <jetty.version>11.0.24</jetty.version>
         <gson.version>2.11.0</gson.version>
         <commons-fileupload2-jakarta-servlet6.version>2.0.0-M2</commons-fileupload2-jakarta-servlet6.version>
     </properties>

web-modules/jakarta-servlets-2/src/main/java/com/baeldung/context/ContextServlet.java

@@ -0,0 +1,59 @@
+package com.baeldung.context;
+
+import jakarta.servlet.ServletConfig;
+import jakarta.servlet.ServletContext;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.annotation.WebServlet;
+import jakarta.servlet.http.HttpServlet;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+
+import java.io.IOException;
+
+@WebServlet(ContextServlet.PATH)
+public class ContextServlet extends HttpServlet {
+
+    protected static final String PATH = "/context";
+
+    protected static final String LABEL_FROM_HTTP_SERVLET = "1) From HttpServlet: ";
+    protected static final String LABEL_FROM_SERVLET_CONFIG = "2) From ServletConfig: ";
+    protected static final String LABEL_FROM_HTTP_SERVLET_REQUEST = "3) From HttpServletRequest: ";
+    protected static final String LABEL_FROM_HTTP_SESSION = "4) From HttpSession: ";
+
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
+
+        resp.setContentType("text/plain");
+
+        // 1. Direct Access From the Servlet
+        ServletContext contextFromServlet = this.getServletContext();
+        resp.getWriter()
+            .println(LABEL_FROM_HTTP_SERVLET + contextFromServlet);
+
+        resp.getWriter()
+            .println();
+
+        // 2. Accessing Through the ServletConfig
+        ServletConfig config = this.getServletConfig();
+        ServletContext contextFromConfig = config.getServletContext();
+        resp.getWriter()
+            .println(LABEL_FROM_SERVLET_CONFIG + contextFromConfig);
+
+        resp.getWriter()
+            .println();
+
+        // 3. Getting the Context From the HttpServletRequest (Servlet 3.0+)
+        ServletContext contextFromRequest = req.getServletContext();
+        resp.getWriter()
+            .println(LABEL_FROM_HTTP_SERVLET_REQUEST + contextFromRequest);
+
+        resp.getWriter()
+            .println();
+
+        // 4. Retrieving Through the Session Object
+        ServletContext contextFromSession = req.getSession()
+            .getServletContext();
+        resp.getWriter()
+            .println(LABEL_FROM_HTTP_SESSION + contextFromSession);
+    }
+}

web-modules/jakarta-servlets-2/src/test/java/com/baeldung/context/BaseServletTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.context;
+
+import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.servlet.ServletContextHandler;
+import org.junit.jupiter.api.*;
+
+import java.net.InetSocketAddress;
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+public abstract class BaseServletTest {
+
+    protected HttpClient httpClient;
+    protected Server server;
+
+    protected int port() {
+        return 0; // (random) available port
+    }
+
+    protected String host() {
+        return "localhost";
+    }
+
+    protected String contextPath() {
+        return "/";
+    }
+
+    @BeforeAll
+    void startup() throws Exception {
+        httpClient = new HttpClient();
+        httpClient.start();
+
+        ServletContextHandler context = prepareContextHandler();
+
+        server = new Server(new InetSocketAddress(host(), port()));
+        server.setHandler(context);
+        server.start();
+    }
+
+    private ServletContextHandler prepareContextHandler() {
+        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
+        context.setContextPath(contextPath());
+        configure(context);
+        return context;
+    }
+
+    protected abstract void configure(ServletContextHandler context);
+
+    @AfterAll
+    void shutdown() throws Exception {
+        if (server != null) {
+            server.stop();
+        }
+        if (httpClient != null) {
+            httpClient.stop();
+        }
+    }
+
+    protected String baseUri() {
+        String uri = server.getURI()
+            .toString();
+        return uri.endsWith("/") ? uri.substring(0, uri.length() - 1) : uri;
+    }
+}

web-modules/jakarta-servlets-2/src/test/java/com/baeldung/context/ContextServletUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.context;
+
+import org.apache.http.HttpStatus;
+import org.eclipse.jetty.client.api.ContentResponse;
+import org.eclipse.jetty.servlet.ServletContextHandler;
+import org.junit.jupiter.api.Test;
+
+import java.net.URI;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ContextServletUnitTest extends BaseServletTest {
+
+    private static final List<String> CONTEXT_LABELS = List.of(ContextServlet.LABEL_FROM_HTTP_SERVLET, ContextServlet.LABEL_FROM_SERVLET_CONFIG,
+        ContextServlet.LABEL_FROM_HTTP_SERVLET_REQUEST, ContextServlet.LABEL_FROM_HTTP_SESSION);
+
+    @Override
+    protected void configure(ServletContextHandler ctx) {
+        ctx.addServlet(ContextServlet.class, ContextServlet.PATH);
+    }
+
+    @Test
+    void givenContextServlet_whenGetRequest_thenResponseContainsSameContextInstance() throws Exception {
+        ContentResponse response = httpClient.GET(URI.create(baseUri() + ContextServlet.PATH));
+
+        assertEquals(HttpStatus.SC_OK, response.getStatus());
+
+        String body = response.getContentAsString();
+
+        assertContextLinesIn(body);
+
+        List<String> tokens = parseServletContextTokens(body);
+        assertAllEqual(tokens);
+    }
+
+    private static void assertContextLinesIn(String body) {
+        for (String label : CONTEXT_LABELS) {
+            assertTrue(body.contains(label));
+        }
+    }
+
+    private static List<String> parseServletContextTokens(String body) {
+        List<String> targetLines = body.lines()
+            .filter(line -> CONTEXT_LABELS.stream()
+                .anyMatch(line::startsWith))
+            .collect(Collectors.toList());
+
+        assertEquals(CONTEXT_LABELS.size(), targetLines.size());
+
+        return targetLines.stream()
+            .map(line -> {
+                int indexOf = line.indexOf(':');
+                assertTrue(indexOf >= 0);
+                return line.substring(indexOf + 1)
+                    .trim();
+            })
+            .collect(Collectors.toList());
+    }
+
+    private static void assertAllEqual(List<String> tokens) {
+        Set<String> distinct = Set.copyOf(tokens);
+        assertEquals(1, distinct.size());
+    }
+}