5. Spring Beans Autowiring & Annotation Based Configuration(Autowiring)

 

Autowiring


- Auto-wiring, also known as automatic wiring, is a feature of the Spring Framework that automatically wires beans together by matching the types of the properties, constructor arguments, or method arguments of the beans.

- Spring Autowiring is a feature provided by the Spring IoC (Inversion of Control) container that allows for automatic resolution of dependencies between beans.

- Instead of explicitly configuring the relationships between beans in the XML configuration file using `<constructor-arg>` and `<property>` elements, autowiring allows the Spring container to automatically inject the required dependencies.

- Autowiring in Spring Beans helps in reducing the efforts of writing properties.

- If autowiring is enabled then spring container will take care about injecting the dependencies, and no need to configure into an xml file explicitly.

- Autowiring can't be used to inject primitive and string values, it will only supported if the dependancies are in the form of objects.

- All the Spring Beans autowiring should be specified at autowire attribute inside element  <bean>, </bean>.

- To enable Autowiring, just define the "autowire" attribute in <bean>.

<bean id="employee" class="com.jwt.spring.Employee" autowire="byName"/>


Here are the different autowiring modes in Spring:

    


1. no - It is the default autowiring mode. It means no autowiring by default.

2. byName- The byName mode injects the object dependency according to name of the bean. In such case, property name and bean name must be same. It internally calls setter method.  if the match is found it will inject those beans else it won’t be wired.

3. byType-The byType mode injects the object dependency according to type. So property name and bean name can be different. It internally calls setter method.

4. constructor- This is similar to byType but it applies to the arguments of the constructor. The constructor mode injects the dependency by calling the constructor of the class. It calls the constructor having large number of parameters.

5. autodetect- It is deprecated since Spring 3.



Example of autowiring by type:

<bean id="car" class="com.example.Car" autowire="byType"/>


In this example, if there is a single bean of any type that `Car` requires, Spring will automatically inject it. If there are multiple candidates or none, it will throw an exception unless the ambiguity is resolved.

Autowiring can simplify the configuration process, but it's essential to use it carefully, as it may lead to unexpected behavior in complex applications with multiple beans of the same type. It is crucial to understand the relationships between beans and how autowiring works to use it effectively.


Annotation Based Configuration

Starting from Spring 2.5 it became possible to configure the dependency injection using annotations. So instead of using XML to describe a bean wiring, you can move the bean configuration into the component class itself by using annotations on the relevant class, method, or field declaration.

    



1. @Required : The @Required annotation applies to bean property setter methods.

2. @Autowired : The @Autowired annotation can apply to bean property setter methods, non-setter methods, constructor and properties.

3. @Qualifier : The @Qualifier annotation along with @Autowired can be used to remove the confusion by specifiying which exact bean will be wired.There will be a situation where you will create more than one bean of the same type. But you will want to wire only one of them with the property. For those cases, you have to use @Qualifier annotation in Spring with @Autowired so as to remove the confusion by specifying the bean for wiring.

JSR-250 Annotations: (Java Specification Request) These Spring annotations are supported by Spring Framework including @Resource, @PreDestroy and @PostConstruct annotations. These annotations are not really required as you already have the alternatives.



Limitations of Spring Autowiring:

1. Ambiguity in Autowiring:

- If there are multiple beans of the same type that can be candidates for autowiring, Spring may face ambiguity in choosing the correct bean to inject.


2. Limited Support for Primitive Types:

- Autowiring is primarily designed for autowiring objects and may not work as effectively for autowiring primitive types.

- For autowiring primitive types, it is recommended to use @Value annotation or explicitly inject values through XML or JavaConfig.



Comments

Post a Comment

Popular posts from this blog

1. Spring Overview

Image
  Spring Framework  - The Spring Framework is a comprehensive framework for enterprise Java development.  - It provides a wide range of features and functionalities that simplify the development of Java applications, particularly in the domain of enterprise and web applications.  - The framework is known for its modularity, scalability, and ease of integration. What is Spring  - It was developed by Rod Johnson in 2003. - Spring is a lightweight framework. - Spring is a Dependency injection framework to make java application loosely couple. - Spring framework makes the easy developement of javaEE (enterprise ) application. Why to Learn Spring? - Spring is the most popular application development framework for enterprise Java. Millions of developers around the world use Spring Framework to create high performing, easily testable, and reusable code. - Spring is a tool that helps make it easier to build software, like apps or websites. -  Learning Spring is val...
Read more

2. Spring Framework Module (Architecture)

Image
  Spring Framework Architecture The Spring Framework is a comprehensive framework for enterprise Java development. It provides a modular and organized way to build enterprise-level applications. The framework is divided into several modules, each addressing specific concerns.  Types  1. The Core Container: 2. Data Access / Integration 3. The Web   4. Miscellaneous (AOP)   1. Spring Core Container:    CORE: This module provides the fundamental parts of the framework,  its including the IoC (Inversion of Control) container and Dependency Injection features.   BEAN : It deals with the creation and management of Java objects (beans) and their dependencies.A sophisticated implementation of factory pattern called BeanFactory, is provided by, Bean module. CONTEXT : This module builds on the core and beans modules, providing a way to access application objects and services in a consistent manner. It has access rights for any objects that de...
Read more

10. Spring - MVC Framework

Image
  Introduction to Spring MVC Framework - Spring MVC is used to develop the web applications that uses MVC design pattern. By using Spring MVC we can build flexible and loosely coupled web applications. - The MVC design pattern helps in seperating the business logic, presentation logic and controller logic. - Models are responsible for encapsulating the application data.  - The Views render response to the user with the help of the model object .  - Controllers are responsible for receiving the request from the user and calling the back-end services. Spring MVC will make application development faster, cost effective and flexible. Advantage of Spring MVC Framework - Clear separation of responsibilities because it implements MVC design pattern. - Loose coupling among Model, View and Controller. - Inbuilt front controller. - Simplified Validation implementation. - Simplified Exception Handling. - Internationalization logic is simplified compared to other frameworks. - Spring...
Read more