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
    @Qua         


        

Answer 1

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