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@Resource Annotation in Spring

By Arvind Rai, March 24, 2022
On this page we will learn using @Resource annotation in Spring.
1. The @Resource annotation is JSR-250 javax.annotation.Resource API. Some other JSR-250 annotations are @PostConstruct, and @PreDestroy.
2. The @Resource annotation is used to declare a reference to a resource. The @Resource annotation resolves dependency injection. We can use it in place of @Autowired annotation.
3. In case of field-based and method-based injection, the Spring container will inject the resource when the application is initialized. For class-based injection, resource is injected at runtime.
4.The elements of @Resource annotation are name, type, authenticationType, shareable, mappedName and description.
5. If @Resource annotation is not using name attribute, Spring accesses other beans for matching them by type.

6. The @Resource can be used on a
a. Field
b. Method

7. The @Resource can be used by
a. name attribute
b. type attribute.



@Resource vs @Autowired

1. In Spring, the JSR-250 @Resource and Spring @Autowired both annotations are used to solve dependency injection. The @Resource is supported only for fields and bean property setter methods with a single argument whereas @Autowired applies to fields, constructors, and multi-argument methods.
2. In case when multiple beans are eligible to be injected, we should prefer using @Resource over combination of @Autowired and @Qualifier.
3. When using @Resource annotation at method level, the method can have only one argument. The @Autowired annotation can be used at argument level, so it supports more than one arguments.
4. In case of annotation-driven injection by name, we should prefer JSR-250 @Resource annotation over Spring @Autowired.

@Resource at Field level

Here we are using @Resource on fields. In the below class, the company property will be injected with instance of CompanyDAO. The address property will be injected with instance of AddressDAO.
We are using name attribute of @Resource to specify bean name.
public class EmployeeService {
	@Resource(name="company")
        private CompanyDAO company;

	@Resource(name="address")
	private AddressDAO address;

	public CompanyDAO getCompany() {
		return company;
	}
	public AddressDAO getAddress() {
		return address;
	}
} 
In @Resource(name="company"), the company is the bean name. The name attribute is used to specify bean name.
Find the XML configuration for bean definition.
app-conf.xml
<context:annotation-config/>
<bean class="com.concretepage.EmployeeService"/>
<bean id="address" class="com.concretepage.dao.AddressDAO"/>
<bean id="company" class="com.concretepage.dao.CompanyDAO"/> 

@Resource at Method level

The @Resource annotation is used at setter methods with one argument. Find the code to use @Resource at method level. We are using name attribute to specify bean name.
public class EmployeeService {
	private CompanyDAO company;
	private AddressDAO address;
	
	@Resource(name="company")
	public void setCompany(CompanyDAO company) {
	  this.company = company;
	}
	@Resource(name="address")
	public void setAddress(AddressDAO address) {
	  this.address = address;
	}
        ------
} 
@Resource(name="company") : Injects CompanyDAO.
@Resource(name="address") : Injects AddressDAO.


@Resource by Type

We can inject resource by name as well as by type. Here we will discuss injecting resource by type. The type is an attribute of @Resource annotation.
1. By default, @Resource annotation injects instances by type.
@Resource
private CompanyDAO company; 
Here CompanyDAO will be injected.
2. When more than one beans are eligible to be injected, use type attribute and specify the class type to be injected.
@Resource(type = CompanyDAO.class)
private AppDAO company; 
Here CompanyDAO will be injected.

Find the complete code of our example.
AppDAO.java
package com.concretepage.dao;
public interface AppDAO {
   public String get();
} 
AddressDAO.java
package com.concretepage.dao;
import org.springframework.stereotype.Component;

@Component
public class AddressDAO implements AppDAO {
	public String get() {
		return "Varanasi";
	}
} 
CompanyDAO.java
package com.concretepage.dao;
import org.springframework.stereotype.Component;

@Component
public class CompanyDAO implements AppDAO {
	public String get() {
		return "MyCompany Ltd";
	}
} 
EmployeeService.java
package com.concretepage;
import javax.annotation.Resource;
import org.springframework.stereotype.Service;
import com.concretepage.dao.AddressDAO;
import com.concretepage.dao.AppDAO;
import com.concretepage.dao.CompanyDAO;

@Service
public class EmployeeService {
	@Resource(type = CompanyDAO.class)
        private AppDAO company;
	@Resource(type = AddressDAO.class)
	private AppDAO address;

	public AppDAO getCompany() {
		return company;
	}
	public AppDAO getAddress() {
		return address;
	}
} 
AppConfig.java
package com.concretepage;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("com.concretepage")
public class AppConfig {

} 
SpringDemo.java
package com.concretepage;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class SpringDemo {
	public static void main(String[] args) {
	    AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
	    ctx.register(AppConfig.class);
	    ctx.refresh();
	    EmployeeService employee = ctx.getBean(EmployeeService.class);
	    System.out.println(employee.getAddress().get());
	    System.out.println(employee.getCompany().get());	
	}
} 
Output
Varanasi
MyCompany Ltd 

References

Resource Injection
Spring Reference

Download Source Code

POSTED BY
ARVIND RAI
ARVIND RAI










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