Spring Autowired Annotation

Autowired annotation is used to auowire beans. In the following example, Address bean is auowired in Employee class.

Step 1 : Create new maven project “spring_tuorial”. Project structure looks like below.

Step 2 : Update “pom.xml” file for maven dependencies.

pom.xml

<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> 
 <groupId>spring_tutorial</groupId> 
 <artifactId>spring_tutorial</artifactId> 
 <version>0.0.1-SNAPSHOT</version> 
 <packaging>war</packaging> 
 <name>spring_tutorial</name> 
 <description>spring_tutorial</description> 
 <properties> 
  <org.springframework-version>4.1.5.RELEASE</org.springframework-version> 
 </properties> 

 <dependencies> 
  <dependency> 
   <groupId>org.springframework</groupId> 
   <artifactId>spring-context</artifactId> 
   <version>${org.springframework-version}</version> 
  </dependency> 

 </dependencies> 
</project>

Step 3: Create new package “com.springtutorial.model” under “src/main/java”.

Step 4: Create Address class under the package “com.springtutorial.model”.

package com.springtutorial.model; 

public class Address { 
  private String street; 
  private String city; 
  private String state; 
  private String country; 
  private String pin; 

  public String getStreet() { 
    return street; 
  } 

  public void setStreet(String street) { 
    this.street = street; 
  } 

  public String getCity() { 
    return city; 
  } 

  public void setCity(String city) { 
    this.city = city; 
  } 

  public String getState() { 
    return state; 
  } 

  public void setState(String state) { 
    this.state = state; 
  } 

  public String getCountry() { 
    return country; 
  } 

  public void setCountry(String country) { 
    this.country = country; 
  } 

  public String getPin() { 
    return pin; 
  } 

  public void setPin(String pin) { 
    this.pin = pin; 
  } 

  @Override 
  public String toString() { 
    StringBuilder builder = new StringBuilder(); 
    builder.append("Address [street=").append(street).append(", city=").append(city) 
        .append(", state=").append(state).append(", country=").append(country).append(", pin=") 
        .append(pin).append("]"); 
    return builder.toString(); 
  } 

} 

Step 5: Create “Employee” class under the package “com.springtutorial.model”.

package com.springtutorial.model; 

import org.springframework.beans.factory.annotation.Autowired; 

public class Employee { 
  private String firstName; 
  private String lastName; 
  private int id; 
  
  @Autowired 
  Address address; 

  public String getFirstName() { 
    return firstName; 
  } 

  public void setFirstName(String firstName) { 
    this.firstName = firstName; 
  } 

  public String getLastName() { 
    return lastName; 
  } 

  public void setLastName(String lastName) { 
    this.lastName = lastName; 
  } 

  public int getId() { 
    return id; 
  } 

  public void setId(int id) { 
    this.id = id; 
  } 

  public Address getAddress() { 
    return address; 
  } 

  public void setAddress(Address address) { 
    this.address = address; 
  } 

  @Override 
  public String toString() { 
    return "Employee [firstName=" + firstName + ", lastName=" + lastName + ", id=" + id + 
        ", address=" + address + "]"; 
  } 

} 

@Autowired

 Address address;

address property is autowired, this property is initialized by spring container automatically.

Step 6: Create “spring.xml” file in “src/main/resources”.

spring.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" xmlns:context="http://www.springframework.org/schema/context" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd"> 

 <context:annotation-config /> 

 <bean id="employee" class="com.springtutorial.model.Employee"> 
  <property name="firstName" value="Hari Krishna" /> 
  <property name="lastName" value="Gurram" /> 
  <property name="id" value="553" /> 
 </bean> 

 <bean id="tempAddress" class="com.springtutorial.model.Address"> 
  <property name="street" value="Marthalli" /> 
  <property name="city" value="Bangalore" /> 
  <property name="state" value="Karnataka" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 


</beans>

"spring.xml" is used to assign unique IDs to different beans, to control the creation of objects with different values. You have to make sure that “spring.xml” file is available in CLASSPATH and use the same name in main application while creating application context as shown in Main.java file.

Step 6 : Create package “com.springtutorial.main” under “src/main/java”.

Step 7 : Create Main class under package “com.springtutorial.main”.

package com.springtutorial.main; 

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

import com.springtutorial.model.Employee; 

public class Main { 
  public static void main(String args[]) { 
    ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); 

    Employee emp = (Employee) context.getBean("employee"); 
    System.out.println(emp); 

    ((ClassPathXmlApplicationContext) context).close(); 
  } 
} 

Step 8: Run Main.java,you will get error like below.

Apr 02, 2015 9:10:42 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh 
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1509f8b: startup date [Thu Apr 02 21:10:42 IST 2015]; root of context hierarchy 
Apr 02, 2015 9:10:42 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions 
INFO: Loading XML bean definitions from class path resource [spring.xml] 
Employee [firstName=Hari Krishna, lastName=Gurram, id=553, address=Address [street=Marthalli, city=Bangalore, state=Karnataka, country=India, pin=560037]] 
Apr 02, 2015 9:10:42 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose 
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@1509f8b: startup date [Thu Apr 02 21:10:42 IST 2015]; root of context hierarchy 

Final project structure looks like below.

What if spring.xml defined with two address beans?

spring.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" xmlns:context="http://www.springframework.org/schema/context" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd"> 

 <context:annotation-config /> 

 <bean id="employee" class="com.springtutorial.model.Employee"> 
  <property name="firstName" value="Hari Krishna" /> 
  <property name="lastName" value="Gurram" /> 
  <property name="id" value="553" /> 
 </bean> 

 <bean id="tempAddress" class="com.springtutorial.model.Address"> 
  <property name="street" value="Marthalli" /> 
  <property name="city" value="Bangalore" /> 
  <property name="state" value="Karnataka" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 

 <bean id="permAddress" class="com.springtutorial.model.Address"> 
  <property name="street" value="Ongole" /> 
  <property name="city" value="Ongole" /> 
  <property name="state" value="Andhra Pradesh" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 

</beans>

As you observe i defined two beans( tempAddress, permAddress) of type Address in spring.xml. Run main.java, you will get error like below.

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.springtutorial.model.Address com.springtutorial.model.Employee.address; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.springtutorial.model.Address] is defined: expected single matching bean but found 2: tempAddress,permAddress

Since there are two beans defined for Address class, Spring don't know which one to assign.

How to solve this problem?

a. Autowire by name

Change the name of the Address property in Employee class to match one of bean id in spring.xml.

package com.springtutorial.model; 

import org.springframework.beans.factory.annotation.Autowired; 

public class Employee { 
  private String firstName; 
  private String lastName; 
  private int id; 
  
  @Autowired 
  Address tempAddress; 

  public String getFirstName() { 
    return firstName; 
  } 

  public void setFirstName(String firstName) { 
    this.firstName = firstName; 
  } 

  public String getLastName() { 
    return lastName; 
  } 

  public void setLastName(String lastName) { 
    this.lastName = lastName; 
  } 

  public int getId() { 
    return id; 
  } 

  public void setId(int id) { 
    this.id = id; 
  } 

  public Address getAddress() { 
    return tempAddress; 
  } 

  public void setAddress(Address address) { 
    this.tempAddress = address; 
  } 

  @Override 
  public String toString() { 
    return "Employee [firstName=" + firstName + ", lastName=" + lastName + ", id=" + id + 
        ", address=" + tempAddress + "]"; 
  } 

} 

In the above class, i am using Address name as tempAddress, which matched to one of the Address bean id defined in spring.xml.

b. Using Qualifier

@Qualifier annotation along with @Autowired is used to remove the confusion by specifying which exact bean will be wired.

spring.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" xmlns:context="http://www.springframework.org/schema/context" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd"> 

 <context:annotation-config /> 

 <bean id="employee" class="com.springtutorial.model.Employee"> 
  <property name="firstName" value="Hari Krishna" /> 
  <property name="lastName" value="Gurram" /> 
  <property name="id" value="553" /> 
 </bean> 
 
 <bean id="tempAddress" class="com.springtutorial.model.Address"> 
  <qualifier value="temporaryAddress" /> 
  <property name="street" value="Marthalli" /> 
  <property name="city" value="Bangalore" /> 
  <property name="state" value="Karnataka" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 

 <bean id="permAddress" class="com.springtutorial.model.Address"> 
  <property name="street" value="Ongole" /> 
  <property name="city" value="Ongole" /> 
  <property name="state" value="Andhra Pradesh" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 

</beans>

<bean id="tempAddress" class="com.springtutorial.model.Address">

                  <qualifier value="temporaryAddress" />

                  <property name="street" value="Marthalli" />

                  <property name="city" value="Bangalore" />

                  <property name="state" value="Karnataka" />

                  <property name="country" value="India" />

                  <property name="pin" value="560037" />

         </bean>

For bean id “tempAddress”, qualifier given as “ temporaryAddress”.

Employee.java

package com.springtutorial.model; 

import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.beans.factory.annotation.Qualifier; 

public class Employee { 
  private String firstName; 
  private String lastName; 
  private int id; 
  
  @Autowired 
  @Qualifier("temporaryAddress") 
  Address address; 

  public String getFirstName() { 
    return firstName; 
  } 

  public void setFirstName(String firstName) { 
    this.firstName = firstName; 
  } 

  public String getLastName() { 
    return lastName; 
  } 

  public void setLastName(String lastName) { 
    this.lastName = lastName; 
  } 

  public int getId() { 
    return id; 
  } 

  public void setId(int id) { 
    this.id = id; 
  } 

  public Address getAddress() { 
    return address; 
  } 

  public void setAddress(Address address) { 
    this.address = address; 
  } 

  @Override 
  public String toString() { 
    return "Employee [firstName=" + firstName + ", lastName=" + lastName + ", id=" + id + 
        ", address=" + address + "]"; 
  } 

} 

@Autowired

  @Qualifier("temporaryAddress")

  Address address;

Above statement makes sure, bean with the qualifier “temporaryAddress” is assigned to property address.

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