BAEL-5336 Move code for the article to spring-di-3 (#11807)

* JAVA-7535 Moved ebook specific code snippets to maven-simple module

* COMAUTO-9485 Fixed DB url in spring-project and added missing maven wrapper

* Code for the Spring @Autowired Field Null – Common Causes and Solutions article

* JAVA-7535 Added code for maven-multi-module

* JAVA-7535 Pom formatting

* JAVA-7535 Pom formatting

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Create README.md

* Create README.md

* JAVA-9825: Upgrade log4j version for modules that use log4j-core library
directly

* BAEL-5188 Add CSRF cookie protection + test (#11775)

* BAEL-5188 Add CSRF cookie protection + test

* BAEL-5188 Break long lines of code

* BAEL-5188 Remove line-breaks before semi-colons

* BAEL-5378 Rename exceptions to avoid confusion (#11801)

* BAEL-5336 Move code for the article to spring-di-3

Co-authored-by: Dhawal Kapil <dhawal.kapil@africa.airtel.com>
Co-authored-by: Dhawal Kapil <dhawalkapil@gmail.com>
Co-authored-by: johnA1331 <53036378+johnA1331@users.noreply.github.com>
Co-authored-by: sampadawagde <sampada.aws@gmail.com>
Co-authored-by: Benjamin Caure <bcaure@gmail.com>
Co-authored-by: ashleyfrieze <ashley@incredible.org.uk>

spring-di-3/src/main/java/com/baeldung/autowiring/App.java

@@ -0,0 +1,14 @@
+package com.baeldung.autowiring;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.ComponentScan;
+
+@SpringBootApplication
+public class App {
+
+    public static void main(String[] args) {
+        SpringApplication.run(App.class, args);
+    }
+
+}

spring-di-3/src/main/java/com/baeldung/autowiring/controller/CorrectController.java

@@ -0,0 +1,18 @@
+package com.baeldung.autowiring.controller;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Controller;
+
+import com.baeldung.autowiring.service.MyService;
+
+@Controller
+public class CorrectController {
+    
+    @Autowired
+    MyService myService;
+    
+    public String control() {
+        return myService.serve();
+    }
+
+}

spring-di-3/src/main/java/com/baeldung/autowiring/controller/FlawedController.java

@@ -0,0 +1,15 @@
+package com.baeldung.autowiring.controller;
+
+import org.springframework.stereotype.Controller;
+
+import com.baeldung.autowiring.service.MyService;
+
+@Controller
+public class FlawedController {
+    
+    public String control() {
+        MyService userService = new MyService();
+        return userService.serve();
+    }
+
+}

spring-di-3/src/main/java/com/baeldung/autowiring/service/MyComponent.java

@@ -0,0 +1,10 @@
+package com.baeldung.autowiring.service;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class MyComponent {
+
+    public void doWork() {}
+    
+}

spring-di-3/src/main/java/com/baeldung/autowiring/service/MyService.java

@@ -0,0 +1,19 @@
+package com.baeldung.autowiring.service;
+
+import org.springframework.beans.factory.annotation.Autowired;
+
+/**
+ * The bean corresponding to this class is defined in MyServiceConfiguration
+ * Alternatively, you could choose to decorate this class with @Component or @Service
+ */
+public class MyService {
+    
+    @Autowired
+    MyComponent myComponent;
+    
+    public String serve() {
+        myComponent.doWork();
+        return "success";
+    }
+
+}

spring-di-3/src/main/java/com/baeldung/autowiring/service/MyServiceConfiguration.java

@@ -0,0 +1,14 @@
+package com.baeldung.autowiring.service;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class MyServiceConfiguration {
+
+    @Bean
+    MyService myService() {
+        return new MyService();
+    }
+    
+}

spring-di-3/src/test/java/com/baeldung/autowiring/controller/CorrectControllerIntegrationTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.autowiring.controller;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest
+public class CorrectControllerIntegrationTest {
+    
+    @Autowired
+    CorrectController controller;
+    
+    @Test
+    void whenControl_ThenRunSuccessfully() {
+        assertDoesNotThrow(() -> controller.control());
+    }
+    
+}

spring-di-3/src/test/java/com/baeldung/autowiring/controller/FlawedControllerIntegrationTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.autowiring.controller;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest
+public class FlawedControllerIntegrationTest {
+    
+    private static final Logger LOGGER = LoggerFactory.getLogger(FlawedControllerIntegrationTest.class);
+    
+    @Autowired
+    FlawedController myController;
+
+    @Test
+    void whenControl_ThenThrowNullPointerException() {
+        NullPointerException npe = assertThrows(NullPointerException.class, () -> myController.control());
+        LOGGER.error("Got a NullPointerException", npe);
+    }
+
+}