Add sample code for API prefix article (#11959)

* Add sample code for API prefix article

* Update README.md

spring-boot-modules/spring-boot-mvc-3/src/main/java/com/baeldung/controllerprefix/ApiPrefixController.java

@@ -0,0 +1,25 @@
+package com.baeldung.controllerprefix;
+
+import org.springframework.stereotype.Controller;
+import org.springframework.ui.ModelMap;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.servlet.ModelAndView;
+
+import java.util.Random;
+
+@Controller
+@RequestMapping("/api")
+public class ApiPrefixController {
+
+    @GetMapping
+    public ModelAndView route(ModelMap model) {
+        if(new Random().nextBoolean()) {
+            return new ModelAndView("forward:/endpoint1", model);
+        }
+        else {
+            return new ModelAndView("forward:/endpoint2", model);
+        }
+    }
+}
+

spring-boot-modules/spring-boot-mvc-3/src/main/java/com/baeldung/controllerprefix/ControllerPrefixDemoApp.java

@@ -0,0 +1,29 @@
+package com.baeldung.controllerprefix;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.ResponseBody;
+
+@SpringBootApplication
+public class ControllerPrefixDemoApp {
+    public static void main(String[] args) {
+        SpringApplication.run(ControllerPrefixDemoApp.class, args);
+    }
+}
+
+@Controller
+class EndpointController {
+    @GetMapping("/endpoint1")
+    @ResponseBody
+    public String endpoint1() {
+        return "Hello from endpoint 1";
+    }
+
+    @GetMapping("/endpoint2")
+    @ResponseBody
+    public String endpoint2() {
+        return "Hello from endpoint 2";
+    }
+}