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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

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Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Baeldung)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat=Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag=Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

eBook – Guide Spring Cloud – NPI EA (cat=Spring Cloud)
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eBook – Mockito – NPI EA (tag = Mockito)
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Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.

Get started with mocking and improve your application tests using our Mockito guide:

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eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

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eBook – Reactive – NPI EA (cat=Reactive)
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Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:

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eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

>> Join Pro and download the eBook

eBook – Jackson – NPI EA (cat=Jackson)
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Do JSON right with Jackson

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eBook – HTTP Client – NPI EA (cat=Http Client-Side)
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Get the most out of the Apache HTTP Client

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eBook – Maven – NPI EA (cat = Maven)
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Get Started with Apache Maven:

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eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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eBook – RwS – NPI EA (cat=Spring MVC)
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Building a REST API with Spring?

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Course – LS – NPI EA (cat=Jackson)
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Get started with Spring and Spring Boot, through the Learn Spring course:

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Course – RWSB – NPI EA (cat=REST)
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Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

>> The New “REST With Spring Boot”

Course – LSS – NPI EA (cat=Spring Security)
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Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.

I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.

You can explore the course here:

>> Learn Spring Security

Course – All Access – NPI EA (cat= Spring)
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All Access is finally out, with all of my Spring courses. Learn JUnit is out as well, and Learn Maven is coming fast. And, of course, quite a bit more affordable. Finally.

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Course – LSD – NPI EA (tag=Spring Data JPA)
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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.

Get started with Spring Data JPA through the guided reference course:

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Partner – LambdaTest – NPI EA (cat=Testing)
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End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

>> Automated End-to-End Testing With Playwright

Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – Spring Sale 2025 – NPI (cat=Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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1. Overview

Starting with Spring 2.5, the framework introduced annotations-driven Dependency Injection. The main annotation of this feature is @Autowired. It allows Spring to resolve and inject collaborating beans into our bean.

Further reading:

Spring Component Scanning

Learn about the mechanism behind Spring component scanning, and how you can tweak it to your own needs

Intro to Inversion of Control and Dependency Injection with Spring

A quick introduction to the concepts of Inversion of Control and Dependency Injection, followed by a simple demonstration using the Spring Framework

In this tutorial, we’ll first take a look at how to enable autowiring and the various ways to autowire beans. Afterward, we’ll talk about resolving bean conflicts using @Qualifier annotation, as well as potential exception scenarios.

2. Enabling @Autowired Annotations

The Spring framework enables automatic dependency injection. In other words, by declaring all the bean dependencies in a Spring configuration file, Spring container can autowire relationships between collaborating beans. This is called Spring bean autowiring.

To use Java-based configuration in our application, let’s enable annotation-driven injection to load our Spring configuration:

@Configuration
@ComponentScan("com.baeldung.autowire.sample")
public class AppConfig {}

Alternatively, the <context:annotation-config> annotation is mainly used to activate the dependency injection annotations in Spring XML files.

Moreover, Spring Boot introduces the @SpringBootApplication annotation. This single annotation is equivalent to using @Configuration, @EnableAutoConfiguration, and @ComponentScan.

Let’s use this annotation in the main class of the application:

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

As a result, when we run this Spring Boot application, it will automatically scan the components in the current package and its sub-packages. Thus it will register them in Spring’s Application Context, and allow us to inject beans using @Autowired.

3. Using @Autowired

After enabling annotation injection, we can use autowiring on properties, setters, and constructors.

3.1. @Autowired on Properties

Let’s see how we can annotate a property using @Autowired. This eliminates the need for getters and setters.

First, let’s define a fooFormatter bean:

@Component("fooFormatter")
public class FooFormatter {
    public String format() {
        return "foo";
    }
}

Then, we’ll inject this bean into the FooService bean using @Autowired on the field definition:

@Component
public class FooService {  
    @Autowired
    private FooFormatter fooFormatter;
}

As a result, Spring injects fooFormatter when FooService is created.

3.2. @Autowired on Setters

Now let’s try adding @Autowired annotation on a setter method.

In the following example, the setter method is called with the instance of FooFormatter when FooService is created:

public class FooService {
    private FooFormatter fooFormatter;
    @Autowired
    public void setFormatter(FooFormatter fooFormatter) {
        this.fooFormatter = fooFormatter;
    }
}

3.3. @Autowired on Constructors

Finally, let’s use @Autowired on a constructor.

We’ll see that an instance of FooFormatter is injected by Spring as an argument to the FooService constructor:

public class FooService {
    private FooFormatter fooFormatter;
    @Autowired
    public FooService(FooFormatter fooFormatter) {
        this.fooFormatter = fooFormatter;
    }
}

4. @Autowired and Optional Dependencies

When a bean is being constructed, the @Autowired dependencies should be available. Otherwise, if Spring cannot resolve a bean for wiring, it will throw an exception.

Consequently, it prevents the Spring container from launching successfully with an exception of the form:

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: 
No qualifying bean of type [com.autowire.sample.FooDAO] found for dependency: 
expected at least 1 bean which qualifies as autowire candidate for this dependency. 
Dependency annotations: 
{@org.springframework.beans.factory.annotation.Autowired(required=true)}

To fix this, we need to declare a bean of the required type:

public class FooService {
    @Autowired(required = false)
    private FooDAO dataAccessor; 
}

5. Autowire Disambiguation

By default, Spring resolves @Autowired entries by type. If more than one bean of the same type is available in the container, the framework will throw a fatal exception.

To resolve this conflict, we need to tell Spring explicitly which bean we want to inject.

5.1. Autowiring by @Qualifier

For instance, let’s see how we can use the @Qualifier annotation to indicate the required bean.

First, we’ll define 2 beans of type Formatter:

@Component("fooFormatter")
public class FooFormatter implements Formatter {
    public String format() {
        return "foo";
    }
}
@Component("barFormatter")
public class BarFormatter implements Formatter {
    public String format() {
        return "bar";
    }
}

Now let’s try to inject a Formatter bean into the FooService class:

public class FooService {
    @Autowired
    private Formatter formatter;
}

In our example, there are two concrete implementations of Formatter available for the Spring container. As a result, Spring will throw a NoUniqueBeanDefinitionException exception when constructing the FooService:

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: 
No qualifying bean of type [com.autowire.sample.Formatter] is defined: 
expected single matching bean but found 2: barFormatter,fooFormatter

We can avoid this by narrowing the implementation using a @Qualifier annotation:

public class FooService {
    @Autowired
    @Qualifier("fooFormatter")
    private Formatter formatter;
}

When there are multiple beans of the same type, it’s a good idea to use @Qualifier to avoid ambiguity.

Please note that the value of the @Qualifier annotation matches with the name declared in the @Component annotation of our FooFormatter implementation.

5.2. Autowiring by Custom Qualifier

Spring also allows us to create our own custom @Qualifier annotation. To do so, we should provide the @Qualifier annotation with the definition:

@Qualifier
@Target({
  ElementType.FIELD, ElementType.METHOD, ElementType.TYPE, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface FormatterType {  
    String value();
}

Then we can use the FormatterType within various implementations to specify a custom value:

@FormatterType("Foo")
@Component
public class FooFormatter implements Formatter {
    public String format() {
        return "foo";
    }
}
@FormatterType("Bar")
@Component
public class BarFormatter implements Formatter {
    public String format() {
        return "bar";
    }
}

Finally, our custom Qualifier annotation is ready to use for autowiring:

@Component
public class FooService {  
    @Autowired
    @FormatterType("Foo")
    private Formatter formatter;
}

The value specified in the @Target meta-annotation restricts where to apply the qualifier, which in our example is fields, methods, types, and parameters.

5.3. Autowiring by Name

Spring uses the bean’s name as a default qualifier value. It will inspect the container and look for a bean with the exact name as the property to autowire it.

Hence, in our example, Spring matches the fooFormatter property name to the FooFormatter implementation. Therefore, it injects that specific implementation when constructing FooService:

public class FooService {
 @Autowired 
private Formatter fooFormatter; 
}

6. Conclusion

In this article, we discussed autowiring and the different ways to use it. We also examined ways to solve two common autowiring exceptions caused by either a missing bean or an ambiguous bean injection.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
Baeldung Pro – NPI EA (cat = Baeldung)
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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat = Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag = Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

eBook – HTTP Client – NPI EA (cat=HTTP Client-Side)
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The Apache HTTP Client is a very robust library, suitable for both simple and advanced use cases when testing HTTP endpoints. Check out our guide covering basic request and response handling, as well as security, cookies, timeouts, and more:

>> Download the eBook

eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

>> Download the eBook

eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

>> Join Pro and download the eBook

eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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Course – LS – NPI EA (cat=REST)

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Get started with Spring Boot and with core Spring, through the Learn Spring course:

>> CHECK OUT THE COURSE

Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – Spring Sale 2025 – NPI (All)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Partner – Microsoft – NPI (cat=Spring)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

eBook Jackson – NPI EA – 3 (cat = Jackson)