'What can cause a null pointer exception in my class listener using an autowired dao? [duplicate]

While trying to execute a delete query on registers of the class Alumno, on a many to one relationship with the class Calificacion I get null pointer exception on the autowired repository.

public class AlumnoListener {

    @Autowired
    CalificacionRepositorio calificacionDAO;
    
    @PreRemove
    public void borradoAlumno(Alumno alumno) {
        
        List<Calificacion> list = (List<Calificacion>) calificacionDAO.findAll();

        list.stream().filter(c -> c.getAlumno().equals(alumno)).forEach(calificacionDAO::delete);
    }
}
javaspringspring-boot


Solution 1:[1]

You probably have to create a bean in your applicationContext.xml

<bean id="CalificacionRepositorio" class="com.example.CalificacionRepositorio" autowire="byName"></bean>

Or programmatically in a @Configuration annotated class within your ComponentScan package

@Bean
@Lazy
public CalificacionRepositorio configuraCalificacionRepositorio() {
    return new CalificacionRepositorio();
}

If you have already registered your bean in the application context make sure that the variable name matches the class name. Try replacing calificacionDAO with calificacionRepositorio

Sources

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Source: Stack Overflow

Solution Source
Solution 1 RicardoE

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