Spring CGLIB, transactions and private final field initialization

Question

I have the following class hierarchy in my Spring Boot application:

public abstract class A {

    private final ObjectMapper objectMapper = new ObjectMapper();

    public void method1(Object object) {
        this.objectMapper.writeValueAsString(object);
    }

}

@Component
public class B extends A {

    public void method2() {
        method1();
    }

}

in such case everything is working fine.

But when I add @Transactional(rollbackFor = Exception.class) annotation to method2() declaration, like for example:

public abstract class A {

    private final ObjectMapper objectMapper = new ObjectMapper();

    public void method1() {
        this.objectMapper; // always NULL
    }

}

@Component
public class B extends A {

    @Transactional(rollbackFor = Exception.class)
    public void method2() {
        method1();
    }

}

and execute method2() it fails with NullPointerException in method1() because of this.objectMapper is NULL;

How to let Spring correctly initialize the private final ObjectMapper objectMapper even in case of @Transactional(rollbackFor = Exception.class) is added?

Also, in case of @Transactional annotation the class of this is B$$EnhancerBySpringCGLIB and without annotation is just plain B. So, looks like CGLIB unable to properly initialize private final ObjectMapper objectMapper.. Is there any workarounds how it can be solved?

See https://deinum.biz/2020-07-03-Autowired-Field-Null/#aop for a broader explanation. Mainly due to proxies, remove the `final` keyword from `method2` else it won't work. — M. Deinum, Aug 27 '20 at 12:30

score 1 · Accepted Answer · answered Aug 27 '20 at 12:11

1

Remove the final in your code. You are using @Transactional with CGLIB. How CGLIB works is it creates a proxy by extending your class. Since the below method is final it cannot extend it, since final classes cannot be extended.

@Transactional(rollbackFor = Exception.class)

public final void method2() {
    method1();
}

answered Aug 27 '20 at 12:11

Daniel Jacob

1,455
9
17

Thanks for your answer! Is it possible to do with reflection api or something like this? Because mentioned code in my example is a part of 3rdparty lib. – alexanoid Aug 27 '20 at 12:13
1

I think you can use ReflectionUtils.setField("objectmapper",this.getClass().getSuperclass(), new ObjectMapper()); – Daniel Jacob Aug 27 '20 at 12:29

Spring CGLIB, transactions and private final field initialization

1 Answers1