Spring Steriotype Annotations

Spring supports 4 sterio type annotations like Component, Controller, Repository, Service. Tshese are used for automatic bean detection using classpath scan in Spring framework. 

Annotation	Description
Component	Indicates that an annotated class is a "component".
Controller	Indicates that an annotated class is a "Controller" (e.g. a web controller).
Repository	Indicates that an annotated class is a "Repository" (or "DAO").
Service	Indicates that an annotated class is a "Service" (e.g. a business service facade).

Technically there is not much difference between these annotations, Conceptually these annotations makes beans clear separation. @Component is a generic stereotype for any Spring-managed component. @Repository, @Service, and @Controller are specializations of @Component for more specific use cases, for example, in the persistence, service, and presentation layers, respectively.

Below example uses Component annotation.

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; 

import org.springframework.stereotype.Component; 

@Component 
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; 
import org.springframework.stereotype.Component; 

@Component 
public class Employee { 
  private String firstName; 
  private String lastName; 
  private int id; 

  @Autowired 
  private 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 + "]"; 
  } 

} 

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 /> 
  <context:component-scan base-package="com.springtutorial" /> 

</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.

<context:component-scan base-package="com.springtutorial" />

This tag will do an auto scanning. Assuming each class that has to become a bean is annotated with a correct annotation like @Component (for simple bean) or @Controller (for a servlet control) or @Repository (for DAO classes) and these class are somewhere under the package com.springtutorial, spring will find all of these and create a bean for each one. This is done in 2 scans of the classes - first time it just searches for classes that need to become a bean and maps the injections it needs to be doing, and on the second scan it injects the beansa.

Step 7 : Create package “com.springtutorial.main” under “src/main/java”.

Step 8 : 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 = context.getBean(Employee.class); 
    emp.setId(553); 
    emp.setFirstName("Hari Krishna"); 
    emp.setLastName("Gurram"); 

    emp.getAddress().setCity("Ongole"); 
    emp.getAddress().setCountry("India"); 
    emp.getAddress().setPin("523169"); 
    emp.getAddress().setState("AP"); 
    emp.getAddress().setStreet("abcd"); 

    System.out.println(emp); 

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

Step 9: Run Main.java,you will get error like below.

Apr 03, 2015 10:26:25 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh 
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@249e4f: startup date [Fri Apr 03 22:26:25 IST 2015]; root of context hierarchy 
Apr 03, 2015 10:26:25 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=abcd, city=Ongole, state=AP, country=India, pin=523169]] 
Apr 03, 2015 10:26:25 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose 
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@249e4f: startup date [Fri Apr 03 22:26:25 IST 2015]; root of context hierarchy 

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