Spring Framework Autowiring by Type

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Spring Framework Autowiring by Type

In this article, I am going to discuss Spring Framework Autowiring by Type with Examples. Please read our previous article, where we discussed Spring Framework Autowiring by Name.

What is Autowiring by Type in Spring Framework?

Autowiring by type in Spring is a mechanism where dependencies are automatically injected based on their types. When Autowiring by Type is enabled, Spring searches for beans in the application context that match the type of the dependency being injected and automatically wires them together.

Autowiring by type is convenient when there is only one bean of a particular type in the application context. It simplifies the wiring configuration and reduces the need for explicit qualifiers. It also allows for flexibility in changing the implementation of the dependency, as long as there is only one matching bean type.

Overall, Autowiring by Type provides a convenient way to wire dependencies based on their types, reducing configuration effort. It works well when there is a clear and unambiguous match between the dependency type and a single bean in the application context.

Implementing Autowiring by Type in Spring Framework

Before starting the project, ensure that the required JAR files are in the project’s “Referenced Libraries” folder.

In this article, we will be building upon the project from the previous article. The files and their contents should be as follows:

Kettle.java

public class Kettle
{
    private Drink drink;

    public void pour()
    {System.out.println("Pouring " + drink.getName() + " into cups.");}

    public void setDrink(Drink drink)
    {
        System.out.println("Pouring drink into kettle: " + drink.getName());
        this.drink = drink;
    }
}

This class represents a POJO class which will be used to represent a kettle.

Drink.java

public class Drink
{
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

This class represents a POJO class which will be used to represent a drink. Note that the setters and getters can be automatically added using the “Source Action…” option in the right-click menu of VS Code.

App.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App
{
    public static void main(String[] args)
    {
        ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
        Kettle k = (Kettle) context.getBean("kettle");
        k.pour();
    }
}

The main function creates a student object and a grade object from the beans.xml file. It then prints out the objects to the terminal.

Beans.xml

<?xml version = "1.0" encoding = "UTF-8"?>

<beans xmlns = "http://www.springframework.org/schema/beans"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id = "kettle" class = "Kettle" autowire = "byName"/>
   
   <bean id = "drink" class = "Drink">
     <property name = "name" value = "tea" />
   </bean>

</beans>

We have changed the Autowire Type to Autowire by Type instead of by name. Since there is only one bean of type Drink in the application, additional qualifiers are not required. If there were more than one bean of type Drink,

Step 2: Compile and execute the application. Ensure compilation is successful. Ensure that the output is as expected:

Congratulations! You have completed the Autowiring by type application in Spring Framework!

Benefits of Autowiring by Type in Spring Framework:

• Simplicity and Convenience: Autowiring by type simplifies the configuration process by automatically resolving dependencies based on their types. It eliminates the need for explicit wiring in the configuration files, reducing the overall configuration effort.
• Flexible and Resilient: Autowiring by type provides flexibility in the wiring process. If the dependency type changes or new beans are added to the application context, Autowiring by Type can adapt automatically, reducing the maintenance effort.
• Reduced Configuration Overhead: Autowiring by type eliminates the need to explicitly wire dependencies in the configuration files. This can result in cleaner and more concise configuration files, improving readability and maintainability.

Limitations of Autowiring by Type in Spring Framework:

• Ambiguity with Multiple Beans: Autowiring by type may lead to ambiguity if multiple beans of the same type exist in the application context. In such cases, Spring throws an exception, and you need to resolve the ambiguity by using @Qualifier annotations or switching to another Autowiring mode.
• Limited Control: Autowiring by type reduces the control over the wiring process compared to explicit wiring. Developers rely on Spring to match the dependencies based on their types, which may not always align with their specific needs.
• Potential for Unexpected Dependencies: Autowiring by type may lead to unexpected dependencies being injected if the bean types match unintentionally. This can introduce bugs or unexpected behavior in the application if the wrong bean is injected.

Autowiring by type in Spring offers simplicity and convenience by automatically wiring dependencies based on their types. It reduces configuration overhead and provides flexibility in the wiring process. However, it has limitations in terms of ambiguity with multiple beans and limited control. It’s important to consider the specific requirements and potential risks when deciding to use Autowiring by Type in your Spring applications.

In the next article, I am going to discuss Spring Framework Constructor Autowiring. Here, in this article, I try to explain Spring Framework Autowiring by Type with Examples. I hope you enjoy this Spring Framework Autowiring by Type article.