Spring @Autowired not working

Question

I have some problems wth autowire annotation. My app looks like this:

Here is controller:

@Controller
public class MyController {
    @Autowired
    @Qualifier("someService")
    private SomeService someService;

    ....
}

It's a service layer:

public interface SomeService {
    ...
}

@Service
public class SomeServiceImpl implements SomeService{    
    @Autowired
    @Qualifier("myDAO")
    private MyDAO myDAO;

    ....
}

And DAO layer:

public interface MyDAO{
    ....        
}

@Repository
public class JDBCDAOImpl implements MyDAO {    
    @Autowired
    @Qualifier("dataSource")
    private DataSource dataSource;    
    ....
}

This is a app-service.xml file:

....
<bean id="propertyConfigurer"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
      p:location="/WEB-INF/jdbc.properties" />

<bean id="dataSource"
      class="org.springframework.jdbc.datasource.DriverManagerDataSource"
      p:driverClassName="${jdbc.driverClassName}"
      p:url="${jdbc.url}"
      p:username="${jdbc.username}"
      p:password="${jdbc.password}"/>

<bean id="SomeService" class="com.service.SomeServiceImpl" />    
<bean id="myDAO" class="com.db.JDBCDAOImpl" />    

So... When I'm launching a web-app, MyController Autowires correctly (the someService field correctly injected by SomeServiceImpl class object), but myDAO feild of someService has null value (not injected properly).

Could you help me to find a problem?

P.S. Its interesting, but when I'm changing a "bean id" from myDAO to some another (e.g. myDAO2), system gives me an error, that injecting could not be done, because bean myDAO doesn't exist. So, Spring make an injection, but where it is? And why it's not work correctly?

Answer 1

I found the solution. As Javi said (thanks a lot for you, Javi), I have to annotate DAO and Service layer classes with @Repository and @Service annotation. Now I've tried to write like this:

@Service("someService")
public class SomeServiceImpl implements SomeService{    
    @Autowired
    @Qualifier("myDAO")
    private MyDAO myDAO;

    ....
}

and

@Repository("myDAO")
    public class JDBCDAOImpl implements MyDAO {    
    @Autowired
    @Qualifier("dataSource")
    private DataSource dataSource;    
    ....
}

and all works fine!!!

But I still not found an answer for this quesion: if application will be more complex, and will have more complex structure, where @Repositore and @Service annotation are not preferred for some classes, how to inject correctly beans, which located in lower levels (in a fields of classes, or in a field of fields of classes) (with @Autowire annotation, of course)?

Answer 2

I guess you need <context:annotation-config />.

Answer 3

You can use

<context:component-scan base-package="PATH OF THE BASE PACKAGE"/>  

entry in your configuration .xml file. This entry will scan/read all the stated type and annotations from the java classes.

Answer 4

Important points:

1. Sometimes, @Component may leads to a problem where it might say no default constructor found. The class which is defined as a @Component annotation, it must have a default constructor.
2. Suppose, we have applied @Autowired annotation at field which is a user defined class reference. Now, if we also apply @Component to that class then it will always be initialized with null. So, a field with @Autowired should not have @Component at its class definition.
3. By default @Autowired is byType.

Address bean is autowired at Student class. Let’s see what happens if we apply @Component at Address.java.

CollegeApp.java:

package com.myTest
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import com.bean.Address;
import com.bean.Student;
//Component scanning will for only those classes
//which is defined as @Component. But, all the class should not use
//@Component always even if the class is enabled with auto
//component scanning, specially the class which is Autowired
//Or which is a property of another class 
@Configuration
@ComponentScan(basePackages={"com.bean"})
public class CollegeApp {
    @Bean
    public Address getAddress(){
        return new Address("Elgin street");
}
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context=new AnnotationConfigApplicationContext(CollegeApp.class);
        Student student=context.getBean(Student.class);
        System.out.println(student.toString());
        context.close();
    }
}

We want Elgin street to be autowired with Student address.

Address.java:

package com.bean;
import org.springframework.stereotype.Component;
@Component
public class Address {
    private String street;
    public Address()
    {
    }
    public Address(String theStreet)
    {
        street=theStreet;
    }
    public String toString()
    {
        return (" Address:"+street);
    }
}

Student.java:

package com.bean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class Student {
    private String name;
    private int age;
    private Address address;
    public Student()
    {
    }
    public Student(String theName,int theAge)
    {
        name=theName;age=theAge;
    }
    @Autowired
    public void setAddress(Address address) {
        this.address = address;
    }
    public String toString()
    {
        return ("Name:"+name+" Age:"+age+ " "+address);
    }
}

Output: - Name:null Age:0 Address:null //Address not Autowired here.

To resolve the issue, only change the Address.java as below:

Address.java:

package com.bean;
public class Address {
    private String street;
    public Address(String theStreet)
    {
        street=theStreet;
    }
    public String toString()
    {
        return (" Address:"+street);
    }
}

Output:- Name:null Age:0 Address:Elgin street

Answer 5

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

    <!-- Specifying base package of the Components like Controller, Service, 
        DAO -->
    <context:component-scan base-package="com.jwt" />

    <!-- Getting Database properties -->
    <context:property-placeholder location="classpath:application.properties" />

    <!-- DataSource -->
    <bean class="org.springframework.jdbc.datasource.DriverManagerDataSource"
        id="dataSource">
        <property name="driverClassName" value="${database.driver}"></property>
        <property name="url" value="${database.url}"></property>
        <property name="username" value="${database.user}"></property>
        <property name="password" value="${database.password}"></property>
    </bean>

    <!-- Hibernate SessionFactory -->
    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${hibernate.dialect}</prop>
                <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>
                <prop key="hibernate.format_sql">${hibernate.format_sql}</prop>
                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
            </props>
        </property>
    </bean>

</beans>