autowire null in the abstract class

Question

I had an issue to autowire an object in my abstract base class. It always give me null instead of an instance. Please help.

Base class:

public abstract class BaseClass implements IReq<Req> {

    @Autowired
    protected ReqDao dao;

    protected void updateReq() {
         dao.update();
    } 
}

Child class:

@Component
public class ChildClass extends BaseClass {
    ...
}

ReqDao class:

@Component
public class RptRequestDao {
     public void update(){
          ...
     }
}

I am thinking of simply use the update() function in Base class, which means in my ChildClass, I don't override that one. Is this the problem? If it is, what's the normal way to do it? Thanks in advance.

Are you sure you have ReqDao in the context? How do you instanciate and use ChildClass? I reproduced your code above, it works as expected. — Andriy Slobodyanyk, May 20 '17 at 13:31
@AndriySlobodyanyk, I use new ChildClass() to instantiate it. — Laodao, May 20 '17 at 14:16
Possible duplicate of [Spring, abstract class and annotations](https://stackoverflow.com/questions/2921899/spring-abstract-class-and-annotations) — Aelphaeis, Nov 06 '17 at 17:41

Amer Qarabsa · Answer 1 · 2017-05-20T13:06:11.973

0

A bean is created on demand, in your case when you initialize your object, RepoDao is private so it wont be inhereted to the class which will be intialized, you either need to put

@Component
public class ChildClass extends BaseClass {
    @Autowired
    private ReqDao dao;

or make it protected/public in BaseClass, sure public will make it accessible to other classes which violates the encapsulation

edited May 20 '17 at 13:06

answered May 20 '17 at 12:59

Amer Qarabsa

6,412
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protected not public ! – Sikorski May 20 '17 at 13:02
@Sikorski thanks for the note, both of them are applicable but protected is better – Amer Qarabsa May 20 '17 at 13:07
I modified it to protected. Still give me null value. :( `public abstract class BaseClass implements IReq { @Autowired protected ReqDao dao; protected void updateReq() { dao.update(); } }` – Laodao May 20 '17 at 13:14
how do you instantiate your bean? – Amer Qarabsa May 20 '17 at 13:17
@AmerQarabsa, good question. I forgot to post it. update the question. – Laodao May 20 '17 at 13:21
@Zhazi how do you initialize your ChildClass? – Amer Qarabsa May 20 '17 at 13:25
@AmerQarabsa, I use new ChildClass() to instantiate it. – Laodao May 20 '17 at 14:16
1

@Zhazi That is the problem , you need just to autowire your variable, your setup is valid only if you let spring initialized it by itself, so instead of new ChildClass() just put on the variable Autowired – Amer Qarabsa May 20 '17 at 14:47

score 0 · Answer 2 · answered Dec 04 '18 at 07:05

Instantiate your child class using @Autowired like this

public class SomeClass{

@Autowired
ChildClass childClass; //IMPORTANT

}

The error occurs when you try to instantiate the childClass like this:

public class SomeClass{

ChildClass childClass = new ChildClass();

}

score -1 · Answer 3 · answered May 20 '17 at 13:04

-1

BaseClass is abstract you can't instantiate it.You need to have your ReqDao in ChildClass to be autowired.Spring will only autowire when it will create an instance of that class.Hope that helps

answered May 20 '17 at 13:04

Nitin Prabhu

624
6
10

Chandan Kumar · Answer 4 · 2020-11-08T19:07:34.437

-1

Check how you are instantiating the child class. Make sure you are NOT using "new" keyword to instantiate child class.

ChildClass cc = new ChildClass() // **Not recommended**

You must autowire the childclass and let spring take care of bean creation.

edited Nov 08 '20 at 19:07

answered Aug 05 '19 at 18:51

Chandan Kumar

1,066
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autowire null in the abstract class

4 Answers4