Code for the Spring @Autowired Field Null – Common Causes and Solutions article (#11792)

spring-5-autowiring-beans/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+	<artifactId>spring-5-autowiring-beans</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>spring-5-autowiring-beans</name>
+
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-boot-2</artifactId>
+		<version>0.0.1-SNAPSHOT</version>
+		<relativePath>../parent-boot-2</relativePath>
+	</parent>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+		</dependency>
+	</dependencies>
+
+</project>

spring-5-autowiring-beans/src/main/java/com/baeldung/autowiring/App.java

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+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-5-autowiring-beans/src/main/java/com/baeldung/autowiring/controller/CorrectController.java

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+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-5-autowiring-beans/src/main/java/com/baeldung/autowiring/controller/FlawedController.java

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+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-5-autowiring-beans/src/main/java/com/baeldung/autowiring/service/MyComponent.java

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

spring-5-autowiring-beans/src/main/java/com/baeldung/autowiring/service/MyService.java

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+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-5-autowiring-beans/src/main/java/com/baeldung/autowiring/service/MyServiceConfiguration.java

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+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-5-autowiring-beans/src/test/java/com/baeldung/autowiring/controller/CorrectControllerIntegrationTest.java

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+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-5-autowiring-beans/src/test/java/com/baeldung/autowiring/controller/FlawedControllerIntegrationTest.java

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+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);
+    }
+
+}