Spring Boot Autowired 服务中的 NullPointerException

Question

I am creating a Spring Boot application and I got a NullPointerException in an @Autowired bean.

I have checked the annotations and I have marked my services interfaces and classes as @Service.

I have also created a Java configuration file to specify the base packages for component scanning but the problem persists.

I am presenting my code so far:

package gr.parisk85.dnd35cg.helper.skill;

@Service
public class BarbarianSkillStrategy implements SkillStrategy {
    private static final double MAX_RANKS = 4;
    private static final double RANK_COST = 1;

    @Autowired
    private DnDClassService dnDClassService;

    @Override
    public List<CharacterSkillDTO> select(List<DnDSkill> dndSkills) {
        List<CharacterSkillDTO> characterSkillDTOList = dndSkills.stream()
                .map(skill -> CharacterSkillMapper.map(skill))
                .collect(Collectors.toList());
        Optional<DnDClass> dnDClass = dnDClassService.findDnDClassByClassName(Constants.BARBARIAN);
        characterSkillDTOList
                .stream()
                .filter(skill -> dnDClass.get().getClassSkills().contains(skill))
                .forEach(skill -> {
                    skill.setMaxRanks(MAX_RANKS);
                    skill.setRankCost(RANK_COST);
                });
        return characterSkillDTOList;
    }
}

The exception is thrown in line:

Optional<DnDClass> dnDClass = dnDClassService.findDnDClassByClassName(Constants.BARBARIAN);

The debugger shows that dnDClassService is null.

Above is the SkillStrategyInterface also marked as @Service:

package gr.parisk85.dnd35cg.helper.skill;

@Service
public interface SkillStrategy {
    List<CharacterSkillDTO> select(List<DnDSkill> dndSkills);
}

The DnDClassService interface:

package gr.parisk85.dnd35cg.service;

@Service
public interface DnDClassService {
    Optional<DnDClass> findDnDClassByClassName(String name);
}

And the Impl class:

package gr.parisk85.dnd35cg.service.impl;

@Service
public class DnDClassServiceImpl implements DnDClassService {
    @Autowired
    private DnDClassRepository dnDClassRepository;

    @Override
    public Optional<DnDClass> findDnDClassByClassName(String name) {
        return dnDClassRepository.findDnDClassByClassName(name);
    }
}

I also wrote a configuration class in case I messed up with the component scanning:

package gr.parisk85.dnd35cg.config;

@Configuration
@ComponentScan(basePackages = {
        "gr.parisk85.dnd35cg.helper.skill",
        "gr.parisk85.dnd35cg.helper",
        "gr.parisk85.dnd35cg.service",
        "gr.parisk85.dnd35cg.service.impl"
})
public class ApplicationConfig {
}

You can find my complete project on my github:

Complete project

Thanks in advance for your help.

Answer 1

The class SkillStrategyFactory is the problem:

public class SkillStrategyFactory {

    private static final Map<String, SkillStrategy> skillStrategyMap;

    static {
        skillStrategyMap = new HashMap<>();
        skillStrategyMap.put(Constants.BARBARIAN, new BarbarianSkillStrategy());
    }

    public static SkillStrategy getStrategy(DnDClass dndClass) {
        return skillStrategyMap.get(dndClass.getClassName());
    }
}

Here, you create the BarbarianSkillStrategy yourself using the default constructor. You need to let Spring do that for you for Autowiring to work. So you could inject it directly or transform the factory to a Spring service and inject every implementation of a SkillStrategy in it.